[v1] SEV-ES TPM enablement fixes

[edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Lendacky, Thomas 4 years, 9 months ago

From: Tom Lendacky <thomas.lendacky@amd.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3345

The TPM support in OVMF performs MMIO accesses during the PEI phase. At
this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
guest will fail attempting to perform MMIO to an encrypted address.

Read the PcdTpmBaseAddress and mark the specification defined range
(0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
the MMIO requests.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
 OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index 6ef77ba7bb21..de60332e9390 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -113,6 +113,7 @@ [Pcd]
 
 [FixedPcd]
   gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
+  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
   gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
   gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
   gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
index dddffdebda4b..d524929f9e10 100644
--- a/OvmfPkg/PlatformPei/AmdSev.c
+++ b/OvmfPkg/PlatformPei/AmdSev.c
@@ -141,6 +141,7 @@ AmdSevInitialize (
   )
 {
   UINT64                            EncryptionMask;
+  UINT64                            TpmBaseAddress;
   RETURN_STATUS                     PcdStatus;
 
   //
@@ -206,6 +207,24 @@ AmdSevInitialize (
     }
   }
 
+  //
+  // PEI TPM support will perform MMIO accesses, be sure this range is not
+  // marked encrypted.
+  //
+  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
+  if (TpmBaseAddress != 0) {
+    RETURN_STATUS  DecryptStatus;
+
+    DecryptStatus = MemEncryptSevClearPageEncMask (
+                      0,
+                      TpmBaseAddress,
+                      EFI_SIZE_TO_PAGES (0x5000),
+                      FALSE
+                      );
+
+    ASSERT_RETURN_ERROR (DecryptStatus);
+  }
+
   //
   // Check and perform SEV-ES initialization if required.
   //
-- 
2.31.0



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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Eric van Tassell 4 years, 9 months ago


On 4/20/21 5:54 PM, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3345
> 
> The TPM support in OVMF performs MMIO accesses during the PEI phase. At

where are the phases defined and how many other are there?

> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
> guest will fail attempting to perform MMIO to an encrypted address.
> 
> Read the PcdTpmBaseAddress and mark the specification defined range
> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
> the MMIO requests.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Min Xu <min.m.xu@intel.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>   OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>   OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>   2 files changed, 20 insertions(+)
> 
> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
> index 6ef77ba7bb21..de60332e9390 100644
> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
> @@ -113,6 +113,7 @@ [Pcd]
>   
>   [FixedPcd]
>     gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>     gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>     gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>     gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
> index dddffdebda4b..d524929f9e10 100644
> --- a/OvmfPkg/PlatformPei/AmdSev.c
> +++ b/OvmfPkg/PlatformPei/AmdSev.c
> @@ -141,6 +141,7 @@ AmdSevInitialize (
>     )
>   {
>     UINT64                            EncryptionMask;
> +  UINT64                            TpmBaseAddress;
>     RETURN_STATUS                     PcdStatus;
>   
>     //
> @@ -206,6 +207,24 @@ AmdSevInitialize (
>       }
>     }
>   
> +  //
> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
> +  // marked encrypted.
> +  //
> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
> +  if (TpmBaseAddress != 0) {
> +    RETURN_STATUS  DecryptStatus;
> +
> +    DecryptStatus = MemEncryptSevClearPageEncMask (
> +                      0,
> +                      TpmBaseAddress,
> +                      EFI_SIZE_TO_PAGES (0x5000),
> +                      FALSE
> +                      );
> +
> +    ASSERT_RETURN_ERROR (DecryptStatus);
> +  }
> +
>     //
>     // Check and perform SEV-ES initialization if required.
>     //
> 


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Andrew Fish via groups.io 4 years, 9 months ago

https://edk2-docs.gitbook.io/edk-ii-build-specification/2_design_discussion/23_boot_sequence
> On Apr 20, 2021, at 11:34 PM, Eric van Tassell <evantass@amd.com> wrote:
> 
> 
> 
>> On 4/20/21 5:54 PM, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3345
>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
> 
> where are the phases defined and how many other are there?
> 
>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>> guest will fail attempting to perform MMIO to an encrypted address.
>> Read the PcdTpmBaseAddress and mark the specification defined range
>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>> the MMIO requests.
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>> Cc: James Bottomley <jejb@linux.ibm.com>
>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>> Cc: Min Xu <min.m.xu@intel.com>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>  2 files changed, 20 insertions(+)
>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
>> index 6ef77ba7bb21..de60332e9390 100644
>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>> @@ -113,6 +113,7 @@ [Pcd]
>>    [FixedPcd]
>>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>> index dddffdebda4b..d524929f9e10 100644
>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>    )
>>  {
>>    UINT64                            EncryptionMask;
>> +  UINT64                            TpmBaseAddress;
>>    RETURN_STATUS                     PcdStatus;
>>      //
>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>      }
>>    }
>>  +  //
>> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
>> +  // marked encrypted.
>> +  //
>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>> +  if (TpmBaseAddress != 0) {
>> +    RETURN_STATUS  DecryptStatus;
>> +
>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>> +                      0,
>> +                      TpmBaseAddress,
>> +                      EFI_SIZE_TO_PAGES (0x5000),
>> +                      FALSE
>> +                      );
>> +
>> +    ASSERT_RETURN_ERROR (DecryptStatus);
>> +  }
>> +
>>    //
>>    // Check and perform SEV-ES initialization if required.
>>    //
> 
> 
> 
> 
> 


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

On 04/21/21 01:17, Eric van Tassell wrote:
> 
> 
> On 4/20/21 5:54 PM, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3345
>>
>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
> 
> where are the phases defined and how many other are there?

See "Figure 1. PI Architecture Firmware Phases" in the PI 1.7 spec,
Volume 1, chapter 2 Overview.

One resource for learning more about the phases is:

https://github.com/tianocore/tianocore.github.io/wiki/UEFI-EDKII-Learning-Dev

Thanks
Laszlo


> 
>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>> guest will fail attempting to perform MMIO to an encrypted address.
>>
>> Read the PcdTpmBaseAddress and mark the specification defined range
>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>> the MMIO requests.
>>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>> Cc: James Bottomley <jejb@linux.ibm.com>
>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>> Cc: Min Xu <min.m.xu@intel.com>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>   OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>   OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>   2 files changed, 20 insertions(+)
>>
>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf
>> b/OvmfPkg/PlatformPei/PlatformPei.inf
>> index 6ef77ba7bb21..de60332e9390 100644
>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>> @@ -113,6 +113,7 @@ [Pcd]
>>     [FixedPcd]
>>     gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>     gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>     gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>     gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>> index dddffdebda4b..d524929f9e10 100644
>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>     )
>>   {
>>     UINT64                            EncryptionMask;
>> +  UINT64                            TpmBaseAddress;
>>     RETURN_STATUS                     PcdStatus;
>>       //
>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>       }
>>     }
>>   +  //
>> +  // PEI TPM support will perform MMIO accesses, be sure this range
>> is not
>> +  // marked encrypted.
>> +  //
>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>> +  if (TpmBaseAddress != 0) {
>> +    RETURN_STATUS  DecryptStatus;
>> +
>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>> +                      0,
>> +                      TpmBaseAddress,
>> +                      EFI_SIZE_TO_PAGES (0x5000),
>> +                      FALSE
>> +                      );
>> +
>> +    ASSERT_RETURN_ERROR (DecryptStatus);
>> +  }
>> +
>>     //
>>     // Check and perform SEV-ES initialization if required.
>>     //
>>
> 
> 
> 
> 
> 



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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

review#2 from scratch:

On 04/21/21 00:54, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3345
> 
> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
> guest will fail attempting to perform MMIO to an encrypted address.

(1) As discussed, please update the commit message, for more clarify
about SEV vs. SEV-ES.

> 
> Read the PcdTpmBaseAddress and mark the specification defined range
> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
> the MMIO requests.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Min Xu <min.m.xu@intel.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
> index 6ef77ba7bb21..de60332e9390 100644
> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
> @@ -113,6 +113,7 @@ [Pcd]
>  
>  [FixedPcd]
>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
> index dddffdebda4b..d524929f9e10 100644
> --- a/OvmfPkg/PlatformPei/AmdSev.c
> +++ b/OvmfPkg/PlatformPei/AmdSev.c
> @@ -141,6 +141,7 @@ AmdSevInitialize (
>    )
>  {
>    UINT64                            EncryptionMask;
> +  UINT64                            TpmBaseAddress;
>    RETURN_STATUS                     PcdStatus;
>  
>    //
> @@ -206,6 +207,24 @@ AmdSevInitialize (
>      }
>    }
>  
> +  //
> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
> +  // marked encrypted.
> +  //
> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
> +  if (TpmBaseAddress != 0) {

It's OK to keep this as a sanity check, yes.

> +    RETURN_STATUS  DecryptStatus;
> +
> +    DecryptStatus = MemEncryptSevClearPageEncMask (
> +                      0,
> +                      TpmBaseAddress,
> +                      EFI_SIZE_TO_PAGES (0x5000),

(2) Should be (UINTN)0x5000, as discussed earlier.

> +                      FALSE
> +                      );
> +
> +    ASSERT_RETURN_ERROR (DecryptStatus);

(3) So this is where the mess begins.

The idea is to delay the dispatch of Tcg2ConfigPei until after
PlatformPei determines if SEV is active, and (in case SEV is active)
PlatformPei decrypts the MMIO range of the TPM.

For this, we need to change the IA32 / X64 DEPEX of Tcg2ConfigPei, from
the current TRUE, to some PPI GUID.

There are two choices for that PPI:

(a) gEfiPeiMemoryDiscoveredPpiGuid

Advantages:

- no new PPI definition needed,

- no new PPI installation needed,

- OvmfPkg/Bhyve/PlatformPei needs no separate change

Disadvantages:

- total abuse of gEfiPeiMemoryDiscoveredPpiGuid

(b) gOvmfTpmMmioAccessiblePpiGuid

Disadvantages:

- this new GUID must be defined in "OvmfPkg.dec", in the [Ppis] section,
in a separate patch; its comment should say "this PPI signals that
accessing the MMIO range of the TPM is possible in the PEI phase,
regardless of memory encryption". The PPI definitions should be kept
alphabetically ordered.

- OvmfPkg/PlatformPei must install this new PPI, with a NULL interface.
(See "mPpiBootMode" as a technical example.) OvmfPkg/PlatformPei must
install this new PPI either when the SEV check at the top of
AmdSevInitialize() fails, or when MemEncryptSevClearPageEncMask() succeeds.

- OvmfPkg/Bhyve/PlatformPei must receive the same update, in a separate
patch. That's because "OvmfPkg/Bhyve/BhyveX64.fdf" includes the same
"Tcg2ConfigPei", but consumes "OvmfPkg/Bhyve/PlatformPei" rather than
"OvmfPkg/PlatformPei". Tcg2ConfigPei will receive the same
stricter-than-before depex, so something on the bhyve platform too must
produce the new PPI.

Advantages:

- more or less palatable as a concept, with the new PPI precisely
expressing the dependency we have.

In approach (b), the "OvmfPkg/Bhyve/PlatformPei" patch needs to be CC'd
to the Bhyve reviewers. If the Bhyve reviewers determine that such an
update is actually unnecessary, because on Bhyve, there is no TPM
support and/or no SEV support in fact, then *first* we have to create an
independent Bhyve cleanup series, that rips out the TPM and/or SEV
remnants from the OvmfPkg/Bhyve sub-tree.

I prefer approach (b). I'm sorry that it means extra work wrt. Bhyve,
but I strongly believe in keeping all platforms in the tree, and that
means we need to spend time on such changes.

I'm not CC'ing Rebecca and Peter on this message -- we're deep into this
patch review thread, and they'd have no useful context. I suggest simply
including the "OvmfPkg/Bhyve/PlatformPei" patch in the next version of
this series, with a proper explanation in the blurb (patch#0) and on the
"OvmfPkg/Bhyve/PlatformPei" patch. That should give them enough context
to evaluate whether the change is necessary, or whether we should purge
the TPM and/or the SEV bits from Bhyve. You could also ask them just
this question in advance, in a separate email on the list (with
distilled context). Personally I'm unsure if the TPM and SEV bits
survived into Bhyve because those bits are actually put to use there, or
because the initial platform creation / cloning wasn't as minimal as it
could have been.

Note that in case TPM makes sense on bhyve but SEV doesn't, then
"OvmfPkg/Bhyve/PlatformPei" will have to install the new PPI
unconditionally.

Thanks
Laszlo

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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

On 04/23/21 12:26, Laszlo Ersek wrote:
> review#2 from scratch:
> 
> On 04/21/21 00:54, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3345
>>
>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>> guest will fail attempting to perform MMIO to an encrypted address.
> 
> (1) As discussed, please update the commit message, for more clarify
> about SEV vs. SEV-ES.
> 
>>
>> Read the PcdTpmBaseAddress and mark the specification defined range
>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>> the MMIO requests.
>>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>> Cc: James Bottomley <jejb@linux.ibm.com>
>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>> Cc: Min Xu <min.m.xu@intel.com>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>  2 files changed, 20 insertions(+)
>>
>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
>> index 6ef77ba7bb21..de60332e9390 100644
>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>> @@ -113,6 +113,7 @@ [Pcd]
>>  
>>  [FixedPcd]
>>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>> index dddffdebda4b..d524929f9e10 100644
>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>    )
>>  {
>>    UINT64                            EncryptionMask;
>> +  UINT64                            TpmBaseAddress;
>>    RETURN_STATUS                     PcdStatus;
>>  
>>    //
>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>      }
>>    }
>>  
>> +  //
>> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
>> +  // marked encrypted.
>> +  //
>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>> +  if (TpmBaseAddress != 0) {
> 
> It's OK to keep this as a sanity check, yes.
> 
>> +    RETURN_STATUS  DecryptStatus;
>> +
>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>> +                      0,
>> +                      TpmBaseAddress,
>> +                      EFI_SIZE_TO_PAGES (0x5000),
> 
> (2) Should be (UINTN)0x5000, as discussed earlier.
> 
>> +                      FALSE
>> +                      );
>> +
>> +    ASSERT_RETURN_ERROR (DecryptStatus);
> 
> (3) So this is where the mess begins.
> 
> The idea is to delay the dispatch of Tcg2ConfigPei until after
> PlatformPei determines if SEV is active, and (in case SEV is active)
> PlatformPei decrypts the MMIO range of the TPM.
> 
> For this, we need to change the IA32 / X64 DEPEX of Tcg2ConfigPei, from
> the current TRUE, to some PPI GUID.
> 
> There are two choices for that PPI:
> 
> (a) gEfiPeiMemoryDiscoveredPpiGuid
> 
> Advantages:
> 
> - no new PPI definition needed,
> 
> - no new PPI installation needed,
> 
> - OvmfPkg/Bhyve/PlatformPei needs no separate change
> 
> Disadvantages:
> 
> - total abuse of gEfiPeiMemoryDiscoveredPpiGuid
> 
> 
> (b) gOvmfTpmMmioAccessiblePpiGuid
> 
> Disadvantages:
> 
> - this new GUID must be defined in "OvmfPkg.dec", in the [Ppis] section,
> in a separate patch; its comment should say "this PPI signals that
> accessing the MMIO range of the TPM is possible in the PEI phase,
> regardless of memory encryption". The PPI definitions should be kept
> alphabetically ordered.
> 
> - OvmfPkg/PlatformPei must install this new PPI, with a NULL interface.
> (See "mPpiBootMode" as a technical example.) OvmfPkg/PlatformPei must
> install this new PPI either when the SEV check at the top of
> AmdSevInitialize() fails, or when MemEncryptSevClearPageEncMask() succeeds.
> 
> - OvmfPkg/Bhyve/PlatformPei must receive the same update, in a separate
> patch. That's because "OvmfPkg/Bhyve/BhyveX64.fdf" includes the same
> "Tcg2ConfigPei", but consumes "OvmfPkg/Bhyve/PlatformPei" rather than
> "OvmfPkg/PlatformPei". Tcg2ConfigPei will receive the same
> stricter-than-before depex, so something on the bhyve platform too must
> produce the new PPI.
> 
> Advantages:
> 
> - more or less palatable as a concept, with the new PPI precisely
> expressing the dependency we have.
> 
> 
> In approach (b), the "OvmfPkg/Bhyve/PlatformPei" patch needs to be CC'd
> to the Bhyve reviewers. If the Bhyve reviewers determine that such an
> update is actually unnecessary, because on Bhyve, there is no TPM
> support and/or no SEV support in fact, then *first* we have to create an
> independent Bhyve cleanup series, that rips out the TPM and/or SEV
> remnants from the OvmfPkg/Bhyve sub-tree.
> 
> 
> I prefer approach (b). I'm sorry that it means extra work wrt. Bhyve,
> but I strongly believe in keeping all platforms in the tree, and that
> means we need to spend time on such changes.
> 
> I'm not CC'ing Rebecca and Peter on this message -- we're deep into this
> patch review thread, and they'd have no useful context. I suggest simply
> including the "OvmfPkg/Bhyve/PlatformPei" patch in the next version of
> this series, with a proper explanation in the blurb (patch#0) and on the
> "OvmfPkg/Bhyve/PlatformPei" patch. That should give them enough context
> to evaluate whether the change is necessary, or whether we should purge
> the TPM and/or the SEV bits from Bhyve. You could also ask them just
> this question in advance, in a separate email on the list (with
> distilled context). Personally I'm unsure if the TPM and SEV bits
> survived into Bhyve because those bits are actually put to use there, or
> because the initial platform creation / cloning wasn't as minimal as it
> could have been.
> 
> Note that in case TPM makes sense on bhyve but SEV doesn't, then
> "OvmfPkg/Bhyve/PlatformPei" will have to install the new PPI
> unconditionally.

I've had a further idea on this.

You could add an entirely new PEIM just for this. The entry point
function of the PEIM would check for SEV, decrypt the TPM range if SEV
were active, and then install gOvmfTpmMmioAccessiblePpiGuid
(unconditionally). The exit status of the PEIM would always be
EFI_ABORTED, because there would be no need to keep the PEIM resident.

The new PEIM would have a DEPEX on gEfiPeiMemoryDiscoveredPpiGuid, to
make sure that potential page table splitting for the potential MMIO
range decryption could be satisfied from permanent PEI RAM.

The new PEIM would be included in the DSC and FDF files of the usual
three OVMF platforms, and in the Bhyve platform -- dependent on the
TPM_ENABLE build flag.

There are several advantages to such a separate PEIM:

- For Bhyve, the update is minimal. Just include one line in each of the
FDF and the DSC files. No need to customize an existent
platform-specific PEIM, no code duplication between two PlatformPei modules.

- The new PEIM would depend on the TPM_ENABLE build flag, so it would
only be included in the firmware binaries if and only if Tcg2ConfigPei
were. No useless PPI installation would occur in the absence of TPM_ENABLE.

- No need to check PcdTpmBaseAddress for nullity in the new PEIM, before
the decryption, as TPM_ENABLE guarantees (on IA32/X64) that the PCD
already has the right value.

- The new logic would be properly ordered between PlatformPei and
Tcg2ConfigPei, namely due to the use of two such PPI GUIDs in DEPEXes
that actually make sense. PlatformPei -> TPM MMIO decryptor PEIM ordered
via "memory discovered" (needed for potential page table splitting), TPM
MMIO decryptor PEIM -> Tcg2ConfigPei ordered via "TPM MMIO decrypted".

You could place the new PEIM at:

  OvmfPkg/Tcg/TpmMmioSevDecryptPei

If you haven't lost your patience with me yet, I'd really appreciate if
you could investigate this!

Thanks!
Laszlo



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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

On 04/23/21 15:04, Laszlo Ersek wrote:

> There are several advantages to such a separate PEIM:
> 
> - For Bhyve, the update is minimal. Just include one line in each of the
> FDF and the DSC files. No need to customize an existent
> platform-specific PEIM, no code duplication between two PlatformPei modules.

OTOH, you'd have to update OvmfPkg/AmdSev/AmdSevX64.* too.

Thanks
Laszlo



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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Lendacky, Thomas 4 years, 9 months ago

On 4/23/21 8:04 AM, Laszlo Ersek wrote:
> On 04/23/21 12:26, Laszlo Ersek wrote:
>> review#2 from scratch:
>>
>> On 04/21/21 00:54, Tom Lendacky wrote:
>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>>
>>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3345&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Ca24cbb3f52404e466fe808d906585034%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637547798659640707%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=o2rAydWG7jenRhqbZx3oDffZhlCUimJL9f9Tpmy4etk%3D&amp;reserved=0
>>>
>>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
>>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>>> guest will fail attempting to perform MMIO to an encrypted address.
>>
>> (1) As discussed, please update the commit message, for more clarify
>> about SEV vs. SEV-ES.
>>
>>>
>>> Read the PcdTpmBaseAddress and mark the specification defined range
>>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>>> the MMIO requests.
>>>
>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>>> Cc: James Bottomley <jejb@linux.ibm.com>
>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>> Cc: Min Xu <min.m.xu@intel.com>
>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>> ---
>>>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>>  2 files changed, 20 insertions(+)
>>>
>>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
>>> index 6ef77ba7bb21..de60332e9390 100644
>>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>>> @@ -113,6 +113,7 @@ [Pcd]
>>>  
>>>  [FixedPcd]
>>>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>>> index dddffdebda4b..d524929f9e10 100644
>>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>>    )
>>>  {
>>>    UINT64                            EncryptionMask;
>>> +  UINT64                            TpmBaseAddress;
>>>    RETURN_STATUS                     PcdStatus;
>>>  
>>>    //
>>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>>      }
>>>    }
>>>  
>>> +  //
>>> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
>>> +  // marked encrypted.
>>> +  //
>>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>>> +  if (TpmBaseAddress != 0) {
>>
>> It's OK to keep this as a sanity check, yes.
>>
>>> +    RETURN_STATUS  DecryptStatus;
>>> +
>>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>>> +                      0,
>>> +                      TpmBaseAddress,
>>> +                      EFI_SIZE_TO_PAGES (0x5000),
>>
>> (2) Should be (UINTN)0x5000, as discussed earlier.
>>
>>> +                      FALSE
>>> +                      );
>>> +
>>> +    ASSERT_RETURN_ERROR (DecryptStatus);
>>
>> (3) So this is where the mess begins.
>>
>> The idea is to delay the dispatch of Tcg2ConfigPei until after
>> PlatformPei determines if SEV is active, and (in case SEV is active)
>> PlatformPei decrypts the MMIO range of the TPM.
>>
>> For this, we need to change the IA32 / X64 DEPEX of Tcg2ConfigPei, from
>> the current TRUE, to some PPI GUID.
>>
>> There are two choices for that PPI:
>>
>> (a) gEfiPeiMemoryDiscoveredPpiGuid
>>
>> Advantages:
>>
>> - no new PPI definition needed,
>>
>> - no new PPI installation needed,
>>
>> - OvmfPkg/Bhyve/PlatformPei needs no separate change
>>
>> Disadvantages:
>>
>> - total abuse of gEfiPeiMemoryDiscoveredPpiGuid
>>
>>
>> (b) gOvmfTpmMmioAccessiblePpiGuid
>>
>> Disadvantages:
>>
>> - this new GUID must be defined in "OvmfPkg.dec", in the [Ppis] section,
>> in a separate patch; its comment should say "this PPI signals that
>> accessing the MMIO range of the TPM is possible in the PEI phase,
>> regardless of memory encryption". The PPI definitions should be kept
>> alphabetically ordered.
>>
>> - OvmfPkg/PlatformPei must install this new PPI, with a NULL interface.
>> (See "mPpiBootMode" as a technical example.) OvmfPkg/PlatformPei must
>> install this new PPI either when the SEV check at the top of
>> AmdSevInitialize() fails, or when MemEncryptSevClearPageEncMask() succeeds.
>>
>> - OvmfPkg/Bhyve/PlatformPei must receive the same update, in a separate
>> patch. That's because "OvmfPkg/Bhyve/BhyveX64.fdf" includes the same
>> "Tcg2ConfigPei", but consumes "OvmfPkg/Bhyve/PlatformPei" rather than
>> "OvmfPkg/PlatformPei". Tcg2ConfigPei will receive the same
>> stricter-than-before depex, so something on the bhyve platform too must
>> produce the new PPI.
>>
>> Advantages:
>>
>> - more or less palatable as a concept, with the new PPI precisely
>> expressing the dependency we have.
>>
>>
>> In approach (b), the "OvmfPkg/Bhyve/PlatformPei" patch needs to be CC'd
>> to the Bhyve reviewers. If the Bhyve reviewers determine that such an
>> update is actually unnecessary, because on Bhyve, there is no TPM
>> support and/or no SEV support in fact, then *first* we have to create an
>> independent Bhyve cleanup series, that rips out the TPM and/or SEV
>> remnants from the OvmfPkg/Bhyve sub-tree.
>>
>>
>> I prefer approach (b). I'm sorry that it means extra work wrt. Bhyve,
>> but I strongly believe in keeping all platforms in the tree, and that
>> means we need to spend time on such changes.
>>
>> I'm not CC'ing Rebecca and Peter on this message -- we're deep into this
>> patch review thread, and they'd have no useful context. I suggest simply
>> including the "OvmfPkg/Bhyve/PlatformPei" patch in the next version of
>> this series, with a proper explanation in the blurb (patch#0) and on the
>> "OvmfPkg/Bhyve/PlatformPei" patch. That should give them enough context
>> to evaluate whether the change is necessary, or whether we should purge
>> the TPM and/or the SEV bits from Bhyve. You could also ask them just
>> this question in advance, in a separate email on the list (with
>> distilled context). Personally I'm unsure if the TPM and SEV bits
>> survived into Bhyve because those bits are actually put to use there, or
>> because the initial platform creation / cloning wasn't as minimal as it
>> could have been.
>>
>> Note that in case TPM makes sense on bhyve but SEV doesn't, then
>> "OvmfPkg/Bhyve/PlatformPei" will have to install the new PPI
>> unconditionally.
> 
> I've had a further idea on this.
> 
> You could add an entirely new PEIM just for this. The entry point
> function of the PEIM would check for SEV, decrypt the TPM range if SEV
> were active, and then install gOvmfTpmMmioAccessiblePpiGuid
> (unconditionally). The exit status of the PEIM would always be
> EFI_ABORTED, because there would be no need to keep the PEIM resident.
> 
> The new PEIM would have a DEPEX on gEfiPeiMemoryDiscoveredPpiGuid, to
> make sure that potential page table splitting for the potential MMIO
> range decryption could be satisfied from permanent PEI RAM.
> 
> The new PEIM would be included in the DSC and FDF files of the usual
> three OVMF platforms, and in the Bhyve platform -- dependent on the
> TPM_ENABLE build flag.
> 
> There are several advantages to such a separate PEIM:
> 
> - For Bhyve, the update is minimal. Just include one line in each of the
> FDF and the DSC files. No need to customize an existent
> platform-specific PEIM, no code duplication between two PlatformPei modules.
> 
> - The new PEIM would depend on the TPM_ENABLE build flag, so it would
> only be included in the firmware binaries if and only if Tcg2ConfigPei
> were. No useless PPI installation would occur in the absence of TPM_ENABLE.
> 
> - No need to check PcdTpmBaseAddress for nullity in the new PEIM, before
> the decryption, as TPM_ENABLE guarantees (on IA32/X64) that the PCD
> already has the right value.
> 
> - The new logic would be properly ordered between PlatformPei and
> Tcg2ConfigPei, namely due to the use of two such PPI GUIDs in DEPEXes
> that actually make sense. PlatformPei -> TPM MMIO decryptor PEIM ordered
> via "memory discovered" (needed for potential page table splitting), TPM
> MMIO decryptor PEIM -> Tcg2ConfigPei ordered via "TPM MMIO decrypted".
> 
> You could place the new PEIM at:
> 
>   OvmfPkg/Tcg/TpmMmioSevDecryptPei
> 
> If you haven't lost your patience with me yet, I'd really appreciate if
> you could investigate this!
> 

So far, this appears to be working nicely. I'm new at the whole PEIM
thing, so hopefully I haven't missed anything. I should be submitting the
patches soon for review.

One thing I found is that the Bhyve package makes reference to the
OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
think that TPM enablement has been tested. I didn't update the Bhyve
support for that reason.

Thanks,
Tom

> Thanks!
> Laszlo
> 


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Lendacky, Thomas 4 years, 9 months ago

On 4/23/21 12:41 PM, Tom Lendacky wrote:
> On 4/23/21 8:04 AM, Laszlo Ersek wrote:
>> On 04/23/21 12:26, Laszlo Ersek wrote:
>>> review#2 from scratch:
>>>
>>> On 04/21/21 00:54, Tom Lendacky wrote:
>>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>>>
>>>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3345&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Ca24cbb3f52404e466fe808d906585034%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637547798659640707%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=o2rAydWG7jenRhqbZx3oDffZhlCUimJL9f9Tpmy4etk%3D&amp;reserved=0
>>>>
>>>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
>>>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>>>> guest will fail attempting to perform MMIO to an encrypted address.
>>>
>>> (1) As discussed, please update the commit message, for more clarify
>>> about SEV vs. SEV-ES.
>>>
>>>>
>>>> Read the PcdTpmBaseAddress and mark the specification defined range
>>>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>>>> the MMIO requests.
>>>>
>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>>>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>>>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>>>> Cc: James Bottomley <jejb@linux.ibm.com>
>>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>>> Cc: Min Xu <min.m.xu@intel.com>
>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>>> ---
>>>>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>>>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>>>  2 files changed, 20 insertions(+)
>>>>
>>>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>> index 6ef77ba7bb21..de60332e9390 100644
>>>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>>>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>> @@ -113,6 +113,7 @@ [Pcd]
>>>>  
>>>>  [FixedPcd]
>>>>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>>>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>>>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>>>> index dddffdebda4b..d524929f9e10 100644
>>>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>>>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>>>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>>>    )
>>>>  {
>>>>    UINT64                            EncryptionMask;
>>>> +  UINT64                            TpmBaseAddress;
>>>>    RETURN_STATUS                     PcdStatus;
>>>>  
>>>>    //
>>>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>>>      }
>>>>    }
>>>>  
>>>> +  //
>>>> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
>>>> +  // marked encrypted.
>>>> +  //
>>>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>>>> +  if (TpmBaseAddress != 0) {
>>>
>>> It's OK to keep this as a sanity check, yes.
>>>
>>>> +    RETURN_STATUS  DecryptStatus;
>>>> +
>>>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>>>> +                      0,
>>>> +                      TpmBaseAddress,
>>>> +                      EFI_SIZE_TO_PAGES (0x5000),
>>>
>>> (2) Should be (UINTN)0x5000, as discussed earlier.
>>>
>>>> +                      FALSE
>>>> +                      );
>>>> +
>>>> +    ASSERT_RETURN_ERROR (DecryptStatus);
>>>
>>> (3) So this is where the mess begins.
>>>
>>> The idea is to delay the dispatch of Tcg2ConfigPei until after
>>> PlatformPei determines if SEV is active, and (in case SEV is active)
>>> PlatformPei decrypts the MMIO range of the TPM.
>>>
>>> For this, we need to change the IA32 / X64 DEPEX of Tcg2ConfigPei, from
>>> the current TRUE, to some PPI GUID.
>>>
>>> There are two choices for that PPI:
>>>
>>> (a) gEfiPeiMemoryDiscoveredPpiGuid
>>>
>>> Advantages:
>>>
>>> - no new PPI definition needed,
>>>
>>> - no new PPI installation needed,
>>>
>>> - OvmfPkg/Bhyve/PlatformPei needs no separate change
>>>
>>> Disadvantages:
>>>
>>> - total abuse of gEfiPeiMemoryDiscoveredPpiGuid
>>>
>>>
>>> (b) gOvmfTpmMmioAccessiblePpiGuid
>>>
>>> Disadvantages:
>>>
>>> - this new GUID must be defined in "OvmfPkg.dec", in the [Ppis] section,
>>> in a separate patch; its comment should say "this PPI signals that
>>> accessing the MMIO range of the TPM is possible in the PEI phase,
>>> regardless of memory encryption". The PPI definitions should be kept
>>> alphabetically ordered.
>>>
>>> - OvmfPkg/PlatformPei must install this new PPI, with a NULL interface.
>>> (See "mPpiBootMode" as a technical example.) OvmfPkg/PlatformPei must
>>> install this new PPI either when the SEV check at the top of
>>> AmdSevInitialize() fails, or when MemEncryptSevClearPageEncMask() succeeds.
>>>
>>> - OvmfPkg/Bhyve/PlatformPei must receive the same update, in a separate
>>> patch. That's because "OvmfPkg/Bhyve/BhyveX64.fdf" includes the same
>>> "Tcg2ConfigPei", but consumes "OvmfPkg/Bhyve/PlatformPei" rather than
>>> "OvmfPkg/PlatformPei". Tcg2ConfigPei will receive the same
>>> stricter-than-before depex, so something on the bhyve platform too must
>>> produce the new PPI.
>>>
>>> Advantages:
>>>
>>> - more or less palatable as a concept, with the new PPI precisely
>>> expressing the dependency we have.
>>>
>>>
>>> In approach (b), the "OvmfPkg/Bhyve/PlatformPei" patch needs to be CC'd
>>> to the Bhyve reviewers. If the Bhyve reviewers determine that such an
>>> update is actually unnecessary, because on Bhyve, there is no TPM
>>> support and/or no SEV support in fact, then *first* we have to create an
>>> independent Bhyve cleanup series, that rips out the TPM and/or SEV
>>> remnants from the OvmfPkg/Bhyve sub-tree.
>>>
>>>
>>> I prefer approach (b). I'm sorry that it means extra work wrt. Bhyve,
>>> but I strongly believe in keeping all platforms in the tree, and that
>>> means we need to spend time on such changes.
>>>
>>> I'm not CC'ing Rebecca and Peter on this message -- we're deep into this
>>> patch review thread, and they'd have no useful context. I suggest simply
>>> including the "OvmfPkg/Bhyve/PlatformPei" patch in the next version of
>>> this series, with a proper explanation in the blurb (patch#0) and on the
>>> "OvmfPkg/Bhyve/PlatformPei" patch. That should give them enough context
>>> to evaluate whether the change is necessary, or whether we should purge
>>> the TPM and/or the SEV bits from Bhyve. You could also ask them just
>>> this question in advance, in a separate email on the list (with
>>> distilled context). Personally I'm unsure if the TPM and SEV bits
>>> survived into Bhyve because those bits are actually put to use there, or
>>> because the initial platform creation / cloning wasn't as minimal as it
>>> could have been.
>>>
>>> Note that in case TPM makes sense on bhyve but SEV doesn't, then
>>> "OvmfPkg/Bhyve/PlatformPei" will have to install the new PPI
>>> unconditionally.
>>
>> I've had a further idea on this.
>>
>> You could add an entirely new PEIM just for this. The entry point
>> function of the PEIM would check for SEV, decrypt the TPM range if SEV
>> were active, and then install gOvmfTpmMmioAccessiblePpiGuid
>> (unconditionally). The exit status of the PEIM would always be
>> EFI_ABORTED, because there would be no need to keep the PEIM resident.
>>
>> The new PEIM would have a DEPEX on gEfiPeiMemoryDiscoveredPpiGuid, to
>> make sure that potential page table splitting for the potential MMIO
>> range decryption could be satisfied from permanent PEI RAM.
>>
>> The new PEIM would be included in the DSC and FDF files of the usual
>> three OVMF platforms, and in the Bhyve platform -- dependent on the
>> TPM_ENABLE build flag.
>>
>> There are several advantages to such a separate PEIM:
>>
>> - For Bhyve, the update is minimal. Just include one line in each of the
>> FDF and the DSC files. No need to customize an existent
>> platform-specific PEIM, no code duplication between two PlatformPei modules.
>>
>> - The new PEIM would depend on the TPM_ENABLE build flag, so it would
>> only be included in the firmware binaries if and only if Tcg2ConfigPei
>> were. No useless PPI installation would occur in the absence of TPM_ENABLE.
>>
>> - No need to check PcdTpmBaseAddress for nullity in the new PEIM, before
>> the decryption, as TPM_ENABLE guarantees (on IA32/X64) that the PCD
>> already has the right value.
>>
>> - The new logic would be properly ordered between PlatformPei and
>> Tcg2ConfigPei, namely due to the use of two such PPI GUIDs in DEPEXes
>> that actually make sense. PlatformPei -> TPM MMIO decryptor PEIM ordered
>> via "memory discovered" (needed for potential page table splitting), TPM
>> MMIO decryptor PEIM -> Tcg2ConfigPei ordered via "TPM MMIO decrypted".
>>
>> You could place the new PEIM at:
>>
>>   OvmfPkg/Tcg/TpmMmioSevDecryptPei
>>
>> If you haven't lost your patience with me yet, I'd really appreciate if
>> you could investigate this!
>>
> 
> So far, this appears to be working nicely. I'm new at the whole PEIM
> thing, so hopefully I haven't missed anything. I should be submitting the
> patches soon for review.

So one thing I failed to do before submitting my previous patch was to
complete my testing against the IA32 and X64 combination build. In this
build, PEI is built as Ia32, and MemEncryptSevClearPageEncMask() will
return UNSUPPORTED causing an ASSERT (since I check the return code). So
there are a few options:

1. SEV works with the current encrypted mapping, it is only the SEV-ES
   support that fails because of the ValidateMmioMemory() check. I can do
   the mapping change just for SEV-ES since it is X64 only. This works,
   because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
   when running in 64-bit.

2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
   the return status.

3. Create Ia32 and X64 versions of internal functions, where the Ia32
   version simply returns SUCCESS because it can't do anything and the X64
   version calls MemEncryptSevClearPageEncMask(), allowing the main code
   to ASSERT on any errors.

I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?

Thanks,
Tom

> 
> One thing I found is that the Bhyve package makes reference to the
> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
> think that TPM enablement has been tested. I didn't update the Bhyve
> support for that reason.
> 
> Thanks,
> Tom
> 
>> Thanks!
>> Laszlo
>>


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

On 04/23/21 22:02, Tom Lendacky wrote:
> On 4/23/21 12:41 PM, Tom Lendacky wrote:
>> On 4/23/21 8:04 AM, Laszlo Ersek wrote:
>>> On 04/23/21 12:26, Laszlo Ersek wrote:
>>>> review#2 from scratch:
>>>>
>>>> On 04/21/21 00:54, Tom Lendacky wrote:
>>>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>>>>
>>>>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3345&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Ca24cbb3f52404e466fe808d906585034%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637547798659640707%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=o2rAydWG7jenRhqbZx3oDffZhlCUimJL9f9Tpmy4etk%3D&amp;reserved=0
>>>>>
>>>>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
>>>>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>>>>> guest will fail attempting to perform MMIO to an encrypted address.
>>>>
>>>> (1) As discussed, please update the commit message, for more clarify
>>>> about SEV vs. SEV-ES.
>>>>
>>>>>
>>>>> Read the PcdTpmBaseAddress and mark the specification defined range
>>>>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>>>>> the MMIO requests.
>>>>>
>>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>>>>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>>>>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>>>>> Cc: James Bottomley <jejb@linux.ibm.com>
>>>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>>>> Cc: Min Xu <min.m.xu@intel.com>
>>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>>>> ---
>>>>>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>>>>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>>>>  2 files changed, 20 insertions(+)
>>>>>
>>>>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>>> index 6ef77ba7bb21..de60332e9390 100644
>>>>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>>>>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>>> @@ -113,6 +113,7 @@ [Pcd]
>>>>>  
>>>>>  [FixedPcd]
>>>>>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>>>>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>>>>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>>>>> index dddffdebda4b..d524929f9e10 100644
>>>>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>>>>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>>>>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>>>>    )
>>>>>  {
>>>>>    UINT64                            EncryptionMask;
>>>>> +  UINT64                            TpmBaseAddress;
>>>>>    RETURN_STATUS                     PcdStatus;
>>>>>  
>>>>>    //
>>>>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>>>>      }
>>>>>    }
>>>>>  
>>>>> +  //
>>>>> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
>>>>> +  // marked encrypted.
>>>>> +  //
>>>>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>>>>> +  if (TpmBaseAddress != 0) {
>>>>
>>>> It's OK to keep this as a sanity check, yes.
>>>>
>>>>> +    RETURN_STATUS  DecryptStatus;
>>>>> +
>>>>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>>>>> +                      0,
>>>>> +                      TpmBaseAddress,
>>>>> +                      EFI_SIZE_TO_PAGES (0x5000),
>>>>
>>>> (2) Should be (UINTN)0x5000, as discussed earlier.
>>>>
>>>>> +                      FALSE
>>>>> +                      );
>>>>> +
>>>>> +    ASSERT_RETURN_ERROR (DecryptStatus);
>>>>
>>>> (3) So this is where the mess begins.
>>>>
>>>> The idea is to delay the dispatch of Tcg2ConfigPei until after
>>>> PlatformPei determines if SEV is active, and (in case SEV is active)
>>>> PlatformPei decrypts the MMIO range of the TPM.
>>>>
>>>> For this, we need to change the IA32 / X64 DEPEX of Tcg2ConfigPei, from
>>>> the current TRUE, to some PPI GUID.
>>>>
>>>> There are two choices for that PPI:
>>>>
>>>> (a) gEfiPeiMemoryDiscoveredPpiGuid
>>>>
>>>> Advantages:
>>>>
>>>> - no new PPI definition needed,
>>>>
>>>> - no new PPI installation needed,
>>>>
>>>> - OvmfPkg/Bhyve/PlatformPei needs no separate change
>>>>
>>>> Disadvantages:
>>>>
>>>> - total abuse of gEfiPeiMemoryDiscoveredPpiGuid
>>>>
>>>>
>>>> (b) gOvmfTpmMmioAccessiblePpiGuid
>>>>
>>>> Disadvantages:
>>>>
>>>> - this new GUID must be defined in "OvmfPkg.dec", in the [Ppis] section,
>>>> in a separate patch; its comment should say "this PPI signals that
>>>> accessing the MMIO range of the TPM is possible in the PEI phase,
>>>> regardless of memory encryption". The PPI definitions should be kept
>>>> alphabetically ordered.
>>>>
>>>> - OvmfPkg/PlatformPei must install this new PPI, with a NULL interface.
>>>> (See "mPpiBootMode" as a technical example.) OvmfPkg/PlatformPei must
>>>> install this new PPI either when the SEV check at the top of
>>>> AmdSevInitialize() fails, or when MemEncryptSevClearPageEncMask() succeeds.
>>>>
>>>> - OvmfPkg/Bhyve/PlatformPei must receive the same update, in a separate
>>>> patch. That's because "OvmfPkg/Bhyve/BhyveX64.fdf" includes the same
>>>> "Tcg2ConfigPei", but consumes "OvmfPkg/Bhyve/PlatformPei" rather than
>>>> "OvmfPkg/PlatformPei". Tcg2ConfigPei will receive the same
>>>> stricter-than-before depex, so something on the bhyve platform too must
>>>> produce the new PPI.
>>>>
>>>> Advantages:
>>>>
>>>> - more or less palatable as a concept, with the new PPI precisely
>>>> expressing the dependency we have.
>>>>
>>>>
>>>> In approach (b), the "OvmfPkg/Bhyve/PlatformPei" patch needs to be CC'd
>>>> to the Bhyve reviewers. If the Bhyve reviewers determine that such an
>>>> update is actually unnecessary, because on Bhyve, there is no TPM
>>>> support and/or no SEV support in fact, then *first* we have to create an
>>>> independent Bhyve cleanup series, that rips out the TPM and/or SEV
>>>> remnants from the OvmfPkg/Bhyve sub-tree.
>>>>
>>>>
>>>> I prefer approach (b). I'm sorry that it means extra work wrt. Bhyve,
>>>> but I strongly believe in keeping all platforms in the tree, and that
>>>> means we need to spend time on such changes.
>>>>
>>>> I'm not CC'ing Rebecca and Peter on this message -- we're deep into this
>>>> patch review thread, and they'd have no useful context. I suggest simply
>>>> including the "OvmfPkg/Bhyve/PlatformPei" patch in the next version of
>>>> this series, with a proper explanation in the blurb (patch#0) and on the
>>>> "OvmfPkg/Bhyve/PlatformPei" patch. That should give them enough context
>>>> to evaluate whether the change is necessary, or whether we should purge
>>>> the TPM and/or the SEV bits from Bhyve. You could also ask them just
>>>> this question in advance, in a separate email on the list (with
>>>> distilled context). Personally I'm unsure if the TPM and SEV bits
>>>> survived into Bhyve because those bits are actually put to use there, or
>>>> because the initial platform creation / cloning wasn't as minimal as it
>>>> could have been.
>>>>
>>>> Note that in case TPM makes sense on bhyve but SEV doesn't, then
>>>> "OvmfPkg/Bhyve/PlatformPei" will have to install the new PPI
>>>> unconditionally.
>>>
>>> I've had a further idea on this.
>>>
>>> You could add an entirely new PEIM just for this. The entry point
>>> function of the PEIM would check for SEV, decrypt the TPM range if SEV
>>> were active, and then install gOvmfTpmMmioAccessiblePpiGuid
>>> (unconditionally). The exit status of the PEIM would always be
>>> EFI_ABORTED, because there would be no need to keep the PEIM resident.
>>>
>>> The new PEIM would have a DEPEX on gEfiPeiMemoryDiscoveredPpiGuid, to
>>> make sure that potential page table splitting for the potential MMIO
>>> range decryption could be satisfied from permanent PEI RAM.
>>>
>>> The new PEIM would be included in the DSC and FDF files of the usual
>>> three OVMF platforms, and in the Bhyve platform -- dependent on the
>>> TPM_ENABLE build flag.
>>>
>>> There are several advantages to such a separate PEIM:
>>>
>>> - For Bhyve, the update is minimal. Just include one line in each of the
>>> FDF and the DSC files. No need to customize an existent
>>> platform-specific PEIM, no code duplication between two PlatformPei modules.
>>>
>>> - The new PEIM would depend on the TPM_ENABLE build flag, so it would
>>> only be included in the firmware binaries if and only if Tcg2ConfigPei
>>> were. No useless PPI installation would occur in the absence of TPM_ENABLE.
>>>
>>> - No need to check PcdTpmBaseAddress for nullity in the new PEIM, before
>>> the decryption, as TPM_ENABLE guarantees (on IA32/X64) that the PCD
>>> already has the right value.
>>>
>>> - The new logic would be properly ordered between PlatformPei and
>>> Tcg2ConfigPei, namely due to the use of two such PPI GUIDs in DEPEXes
>>> that actually make sense. PlatformPei -> TPM MMIO decryptor PEIM ordered
>>> via "memory discovered" (needed for potential page table splitting), TPM
>>> MMIO decryptor PEIM -> Tcg2ConfigPei ordered via "TPM MMIO decrypted".
>>>
>>> You could place the new PEIM at:
>>>
>>>   OvmfPkg/Tcg/TpmMmioSevDecryptPei
>>>
>>> If you haven't lost your patience with me yet, I'd really appreciate if
>>> you could investigate this!
>>>
>>
>> So far, this appears to be working nicely. I'm new at the whole PEIM
>> thing, so hopefully I haven't missed anything. I should be submitting the
>> patches soon for review.
> 
> So one thing I failed to do before submitting my previous patch was to
> complete my testing against the IA32 and X64 combination build. In this
> build, PEI is built as Ia32, and MemEncryptSevClearPageEncMask() will
> return UNSUPPORTED causing an ASSERT (since I check the return code). So
> there are a few options:
> 
> 1. SEV works with the current encrypted mapping, it is only the SEV-ES
>    support that fails because of the ValidateMmioMemory() check. I can do
>    the mapping change just for SEV-ES since it is X64 only. This works,
>    because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
>    when running in 64-bit.

Can we really say "SEV works" though? Because, even using an X64 PEI
phase, and enabling only SEV (not SEV-ES), TPM access will be broken in
the PEI phase. Is my understanding correct?

I think the behavior you currently see is actually what we want, we
should double down on it -- if MemEncryptSevClearPageEncMask() fails,
report an explicit DEBUG_ERROR, and call CpuDeadLoop(). If the firmware
is built with TPM_ENABLE, and SEV is active, then an IA32 PEI phase is
simply unusable. Silently pretending that the TPM is not there, even
though it may have been configured on the QEMU command line, we just
failed to communicate with it, is not a good idea, IMO.

This is somewhat similar IMO to the S3Verification() function in
"OvmfPkg/PlatformPei/Platform.c".

TPM_ENABLE, SEV, IA32 PEI phase: pick any two.

Thanks,
Laszlo

> 
> 2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
>    the return status.
> 
> 3. Create Ia32 and X64 versions of internal functions, where the Ia32
>    version simply returns SUCCESS because it can't do anything and the X64
>    version calls MemEncryptSevClearPageEncMask(), allowing the main code
>    to ASSERT on any errors.
> 
> I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?
> 
> Thanks,
> Tom
> 
>>
>> One thing I found is that the Bhyve package makes reference to the
>> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
>> think that TPM enablement has been tested. I didn't update the Bhyve
>> support for that reason.
>>
>> Thanks,
>> Tom
>>
>>> Thanks!
>>> Laszlo
>>>
> 



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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Lendacky, Thomas 4 years, 9 months ago

On 4/26/21 7:07 AM, Laszlo Ersek wrote:
> On 04/23/21 22:02, Tom Lendacky wrote:
>> On 4/23/21 12:41 PM, Tom Lendacky wrote:
>>> On 4/23/21 8:04 AM, Laszlo Ersek wrote:
>>>> On 04/23/21 12:26, Laszlo Ersek wrote:
>>>>> review#2 from scratch:
>>>>>
>>>>> On 04/21/21 00:54, Tom Lendacky wrote:
>>>>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>>>>>
>>>>>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3345&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Cc8a12e7c1e6a4282963508d908abe333%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637550356650588901%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=3SeLVc3SscAozGX62BSAyWseujfwxzm6qIB%2Fh8ALyq0%3D&amp;reserved=0
>>>>>>
>>>>>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
>>>>>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>>>>>> guest will fail attempting to perform MMIO to an encrypted address.
>>>>>
>>>>> (1) As discussed, please update the commit message, for more clarify
>>>>> about SEV vs. SEV-ES.
>>>>>
>>>>>>
>>>>>> Read the PcdTpmBaseAddress and mark the specification defined range
>>>>>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>>>>>> the MMIO requests.
>>>>>>
>>>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>>>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>>>>>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>>>>>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>>>>>> Cc: James Bottomley <jejb@linux.ibm.com>
>>>>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>>>>> Cc: Min Xu <min.m.xu@intel.com>
>>>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>>>>> ---
>>>>>>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>>>>>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>>>>>  2 files changed, 20 insertions(+)
>>>>>>
>>>>>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>>>> index 6ef77ba7bb21..de60332e9390 100644
>>>>>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>>>>>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>>>> @@ -113,6 +113,7 @@ [Pcd]
>>>>>>  
>>>>>>  [FixedPcd]
>>>>>>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>>>>>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>>>>>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>>>>>> index dddffdebda4b..d524929f9e10 100644
>>>>>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>>>>>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>>>>>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>>>>>    )
>>>>>>  {
>>>>>>    UINT64                            EncryptionMask;
>>>>>> +  UINT64                            TpmBaseAddress;
>>>>>>    RETURN_STATUS                     PcdStatus;
>>>>>>  
>>>>>>    //
>>>>>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>>>>>      }
>>>>>>    }
>>>>>>  
>>>>>> +  //
>>>>>> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
>>>>>> +  // marked encrypted.
>>>>>> +  //
>>>>>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>>>>>> +  if (TpmBaseAddress != 0) {
>>>>>
>>>>> It's OK to keep this as a sanity check, yes.
>>>>>
>>>>>> +    RETURN_STATUS  DecryptStatus;
>>>>>> +
>>>>>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>>>>>> +                      0,
>>>>>> +                      TpmBaseAddress,
>>>>>> +                      EFI_SIZE_TO_PAGES (0x5000),
>>>>>
>>>>> (2) Should be (UINTN)0x5000, as discussed earlier.
>>>>>
>>>>>> +                      FALSE
>>>>>> +                      );
>>>>>> +
>>>>>> +    ASSERT_RETURN_ERROR (DecryptStatus);
>>>>>
>>>>> (3) So this is where the mess begins.
>>>>>
>>>>> The idea is to delay the dispatch of Tcg2ConfigPei until after
>>>>> PlatformPei determines if SEV is active, and (in case SEV is active)
>>>>> PlatformPei decrypts the MMIO range of the TPM.
>>>>>
>>>>> For this, we need to change the IA32 / X64 DEPEX of Tcg2ConfigPei, from
>>>>> the current TRUE, to some PPI GUID.
>>>>>
>>>>> There are two choices for that PPI:
>>>>>
>>>>> (a) gEfiPeiMemoryDiscoveredPpiGuid
>>>>>
>>>>> Advantages:
>>>>>
>>>>> - no new PPI definition needed,
>>>>>
>>>>> - no new PPI installation needed,
>>>>>
>>>>> - OvmfPkg/Bhyve/PlatformPei needs no separate change
>>>>>
>>>>> Disadvantages:
>>>>>
>>>>> - total abuse of gEfiPeiMemoryDiscoveredPpiGuid
>>>>>
>>>>>
>>>>> (b) gOvmfTpmMmioAccessiblePpiGuid
>>>>>
>>>>> Disadvantages:
>>>>>
>>>>> - this new GUID must be defined in "OvmfPkg.dec", in the [Ppis] section,
>>>>> in a separate patch; its comment should say "this PPI signals that
>>>>> accessing the MMIO range of the TPM is possible in the PEI phase,
>>>>> regardless of memory encryption". The PPI definitions should be kept
>>>>> alphabetically ordered.
>>>>>
>>>>> - OvmfPkg/PlatformPei must install this new PPI, with a NULL interface.
>>>>> (See "mPpiBootMode" as a technical example.) OvmfPkg/PlatformPei must
>>>>> install this new PPI either when the SEV check at the top of
>>>>> AmdSevInitialize() fails, or when MemEncryptSevClearPageEncMask() succeeds.
>>>>>
>>>>> - OvmfPkg/Bhyve/PlatformPei must receive the same update, in a separate
>>>>> patch. That's because "OvmfPkg/Bhyve/BhyveX64.fdf" includes the same
>>>>> "Tcg2ConfigPei", but consumes "OvmfPkg/Bhyve/PlatformPei" rather than
>>>>> "OvmfPkg/PlatformPei". Tcg2ConfigPei will receive the same
>>>>> stricter-than-before depex, so something on the bhyve platform too must
>>>>> produce the new PPI.
>>>>>
>>>>> Advantages:
>>>>>
>>>>> - more or less palatable as a concept, with the new PPI precisely
>>>>> expressing the dependency we have.
>>>>>
>>>>>
>>>>> In approach (b), the "OvmfPkg/Bhyve/PlatformPei" patch needs to be CC'd
>>>>> to the Bhyve reviewers. If the Bhyve reviewers determine that such an
>>>>> update is actually unnecessary, because on Bhyve, there is no TPM
>>>>> support and/or no SEV support in fact, then *first* we have to create an
>>>>> independent Bhyve cleanup series, that rips out the TPM and/or SEV
>>>>> remnants from the OvmfPkg/Bhyve sub-tree.
>>>>>
>>>>>
>>>>> I prefer approach (b). I'm sorry that it means extra work wrt. Bhyve,
>>>>> but I strongly believe in keeping all platforms in the tree, and that
>>>>> means we need to spend time on such changes.
>>>>>
>>>>> I'm not CC'ing Rebecca and Peter on this message -- we're deep into this
>>>>> patch review thread, and they'd have no useful context. I suggest simply
>>>>> including the "OvmfPkg/Bhyve/PlatformPei" patch in the next version of
>>>>> this series, with a proper explanation in the blurb (patch#0) and on the
>>>>> "OvmfPkg/Bhyve/PlatformPei" patch. That should give them enough context
>>>>> to evaluate whether the change is necessary, or whether we should purge
>>>>> the TPM and/or the SEV bits from Bhyve. You could also ask them just
>>>>> this question in advance, in a separate email on the list (with
>>>>> distilled context). Personally I'm unsure if the TPM and SEV bits
>>>>> survived into Bhyve because those bits are actually put to use there, or
>>>>> because the initial platform creation / cloning wasn't as minimal as it
>>>>> could have been.
>>>>>
>>>>> Note that in case TPM makes sense on bhyve but SEV doesn't, then
>>>>> "OvmfPkg/Bhyve/PlatformPei" will have to install the new PPI
>>>>> unconditionally.
>>>>
>>>> I've had a further idea on this.
>>>>
>>>> You could add an entirely new PEIM just for this. The entry point
>>>> function of the PEIM would check for SEV, decrypt the TPM range if SEV
>>>> were active, and then install gOvmfTpmMmioAccessiblePpiGuid
>>>> (unconditionally). The exit status of the PEIM would always be
>>>> EFI_ABORTED, because there would be no need to keep the PEIM resident.
>>>>
>>>> The new PEIM would have a DEPEX on gEfiPeiMemoryDiscoveredPpiGuid, to
>>>> make sure that potential page table splitting for the potential MMIO
>>>> range decryption could be satisfied from permanent PEI RAM.
>>>>
>>>> The new PEIM would be included in the DSC and FDF files of the usual
>>>> three OVMF platforms, and in the Bhyve platform -- dependent on the
>>>> TPM_ENABLE build flag.
>>>>
>>>> There are several advantages to such a separate PEIM:
>>>>
>>>> - For Bhyve, the update is minimal. Just include one line in each of the
>>>> FDF and the DSC files. No need to customize an existent
>>>> platform-specific PEIM, no code duplication between two PlatformPei modules.
>>>>
>>>> - The new PEIM would depend on the TPM_ENABLE build flag, so it would
>>>> only be included in the firmware binaries if and only if Tcg2ConfigPei
>>>> were. No useless PPI installation would occur in the absence of TPM_ENABLE.
>>>>
>>>> - No need to check PcdTpmBaseAddress for nullity in the new PEIM, before
>>>> the decryption, as TPM_ENABLE guarantees (on IA32/X64) that the PCD
>>>> already has the right value.
>>>>
>>>> - The new logic would be properly ordered between PlatformPei and
>>>> Tcg2ConfigPei, namely due to the use of two such PPI GUIDs in DEPEXes
>>>> that actually make sense. PlatformPei -> TPM MMIO decryptor PEIM ordered
>>>> via "memory discovered" (needed for potential page table splitting), TPM
>>>> MMIO decryptor PEIM -> Tcg2ConfigPei ordered via "TPM MMIO decrypted".
>>>>
>>>> You could place the new PEIM at:
>>>>
>>>>   OvmfPkg/Tcg/TpmMmioSevDecryptPei
>>>>
>>>> If you haven't lost your patience with me yet, I'd really appreciate if
>>>> you could investigate this!
>>>>
>>>
>>> So far, this appears to be working nicely. I'm new at the whole PEIM
>>> thing, so hopefully I haven't missed anything. I should be submitting the
>>> patches soon for review.
>>
>> So one thing I failed to do before submitting my previous patch was to
>> complete my testing against the IA32 and X64 combination build. In this
>> build, PEI is built as Ia32, and MemEncryptSevClearPageEncMask() will
>> return UNSUPPORTED causing an ASSERT (since I check the return code). So
>> there are a few options:
>>
>> 1. SEV works with the current encrypted mapping, it is only the SEV-ES
>>    support that fails because of the ValidateMmioMemory() check. I can do
>>    the mapping change just for SEV-ES since it is X64 only. This works,
>>    because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
>>    when running in 64-bit.
> 
> Can we really say "SEV works" though? Because, even using an X64 PEI
> phase, and enabling only SEV (not SEV-ES), TPM access will be broken in
> the PEI phase. Is my understanding correct?

Because the memory range is marked as MMIO, we'll take a nested page fault
(NPF). The GPA passed as part of the NPF does not include the c-bit. So we
do in fact work properly with a TPM in SEV. SEV-ES would also work
properly if the mitigation for accessing an encrypted address was removed
from the #VC handler. It is only this added mitigation to protect MMIO
that results in an issue with the TPM in PEI.

> 
> I think the behavior you currently see is actually what we want, we
> should double down on it -- if MemEncryptSevClearPageEncMask() fails,
> report an explicit DEBUG_ERROR, and call CpuDeadLoop(). If the firmware
> is built with TPM_ENABLE, and SEV is active, then an IA32 PEI phase is
> simply unusable. Silently pretending that the TPM is not there, even
> though it may have been configured on the QEMU command line, we just
> failed to communicate with it, is not a good idea, IMO.

However, because the c-bit is not part of the NPF, we do communicate
successfully with the TPM.

So we could actually do following:
 - For IA32:
   - Remove the Depex on gOvmfTpmMmioAccessiblePpiGuid
   - Do not add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf

 - For X64:
   - Add the Depex on gOvmfTpmMmioAccessiblePpiGuid
   - Add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf

That might be confusing, though. So we could just do option #3 below.

Thanks,
Tom

> 
> This is somewhat similar IMO to the S3Verification() function in
> "OvmfPkg/PlatformPei/Platform.c".
> 
> TPM_ENABLE, SEV, IA32 PEI phase: pick any two.
> 
> Thanks,
> Laszlo
> 
>>
>> 2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
>>    the return status.
>>
>> 3. Create Ia32 and X64 versions of internal functions, where the Ia32
>>    version simply returns SUCCESS because it can't do anything and the X64
>>    version calls MemEncryptSevClearPageEncMask(), allowing the main code
>>    to ASSERT on any errors.
>>
>> I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?
>>
>> Thanks,
>> Tom
>>
>>>
>>> One thing I found is that the Bhyve package makes reference to the
>>> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
>>> think that TPM enablement has been tested. I didn't update the Bhyve
>>> support for that reason.
>>>
>>> Thanks,
>>> Tom
>>>
>>>> Thanks!
>>>> Laszlo
>>>>
>>
> 


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Lendacky, Thomas 4 years, 9 months ago

On 4/26/21 9:21 AM, Tom Lendacky wrote:
> On 4/26/21 7:07 AM, Laszlo Ersek wrote:
>> On 04/23/21 22:02, Tom Lendacky wrote:
>>> On 4/23/21 12:41 PM, Tom Lendacky wrote:
>>>> On 4/23/21 8:04 AM, Laszlo Ersek wrote:
>>>>> On 04/23/21 12:26, Laszlo Ersek wrote:
>>>>>> review#2 from scratch:
>>>>>>
>>>>>> On 04/21/21 00:54, Tom Lendacky wrote:
>>>>>>> From: Tom Lendacky <thomas.lendacky@amd.com>

...

>>>>>
>>>>> I've had a further idea on this.
>>>>>
>>>>> You could add an entirely new PEIM just for this. The entry point
>>>>> function of the PEIM would check for SEV, decrypt the TPM range if SEV
>>>>> were active, and then install gOvmfTpmMmioAccessiblePpiGuid
>>>>> (unconditionally). The exit status of the PEIM would always be
>>>>> EFI_ABORTED, because there would be no need to keep the PEIM resident.
>>>>>
>>>>> The new PEIM would have a DEPEX on gEfiPeiMemoryDiscoveredPpiGuid, to
>>>>> make sure that potential page table splitting for the potential MMIO
>>>>> range decryption could be satisfied from permanent PEI RAM.
>>>>>
>>>>> The new PEIM would be included in the DSC and FDF files of the usual
>>>>> three OVMF platforms, and in the Bhyve platform -- dependent on the
>>>>> TPM_ENABLE build flag.
>>>>>
>>>>> There are several advantages to such a separate PEIM:
>>>>>
>>>>> - For Bhyve, the update is minimal. Just include one line in each of the
>>>>> FDF and the DSC files. No need to customize an existent
>>>>> platform-specific PEIM, no code duplication between two PlatformPei modules.
>>>>>
>>>>> - The new PEIM would depend on the TPM_ENABLE build flag, so it would
>>>>> only be included in the firmware binaries if and only if Tcg2ConfigPei
>>>>> were. No useless PPI installation would occur in the absence of TPM_ENABLE.
>>>>>
>>>>> - No need to check PcdTpmBaseAddress for nullity in the new PEIM, before
>>>>> the decryption, as TPM_ENABLE guarantees (on IA32/X64) that the PCD
>>>>> already has the right value.
>>>>>
>>>>> - The new logic would be properly ordered between PlatformPei and
>>>>> Tcg2ConfigPei, namely due to the use of two such PPI GUIDs in DEPEXes
>>>>> that actually make sense. PlatformPei -> TPM MMIO decryptor PEIM ordered
>>>>> via "memory discovered" (needed for potential page table splitting), TPM
>>>>> MMIO decryptor PEIM -> Tcg2ConfigPei ordered via "TPM MMIO decrypted".
>>>>>
>>>>> You could place the new PEIM at:
>>>>>
>>>>>   OvmfPkg/Tcg/TpmMmioSevDecryptPei
>>>>>
>>>>> If you haven't lost your patience with me yet, I'd really appreciate if
>>>>> you could investigate this!
>>>>>
>>>>
>>>> So far, this appears to be working nicely. I'm new at the whole PEIM
>>>> thing, so hopefully I haven't missed anything. I should be submitting the
>>>> patches soon for review.
>>>
>>> So one thing I failed to do before submitting my previous patch was to
>>> complete my testing against the IA32 and X64 combination build. In this
>>> build, PEI is built as Ia32, and MemEncryptSevClearPageEncMask() will
>>> return UNSUPPORTED causing an ASSERT (since I check the return code). So
>>> there are a few options:
>>>
>>> 1. SEV works with the current encrypted mapping, it is only the SEV-ES
>>>    support that fails because of the ValidateMmioMemory() check. I can do
>>>    the mapping change just for SEV-ES since it is X64 only. This works,
>>>    because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
>>>    when running in 64-bit.
>>
>> Can we really say "SEV works" though? Because, even using an X64 PEI
>> phase, and enabling only SEV (not SEV-ES), TPM access will be broken in
>> the PEI phase. Is my understanding correct?
> 
> Because the memory range is marked as MMIO, we'll take a nested page fault
> (NPF). The GPA passed as part of the NPF does not include the c-bit. So we
> do in fact work properly with a TPM in SEV. SEV-ES would also work
> properly if the mitigation for accessing an encrypted address was removed
> from the #VC handler. It is only this added mitigation to protect MMIO
> that results in an issue with the TPM in PEI.

So I'm thinking that I can have TpmMmioSevDecryptPeim.c do this:

  //
  // If SEV or SEV-ES is active, MMIO succeeds against an encrypted physical
  // address because the nested page fault (NPF) that occurs on access does not
  // include the encryption bit in the guest physical address provided to the
  // hypervisor.
  //
  // However, if SEV-ES is active, before performing the actual MMIO, an
  // additional MMIO mitigation check is performed in the #VC handler to ensure
  // that MMIO is being done to an unencrypted address. To prevent guest
  // termination in this scenario, mark the range unencrypted ahead of access.
  //
  if (MemEncryptSevEsIsEnabled ()) {
    // Do MemEncryptSevClearPageEncMask() ...
  }

Let me submit the next version with this and see what you think.

Thanks,
Tom

> 
>>
>> I think the behavior you currently see is actually what we want, we
>> should double down on it -- if MemEncryptSevClearPageEncMask() fails,
>> report an explicit DEBUG_ERROR, and call CpuDeadLoop(). If the firmware
>> is built with TPM_ENABLE, and SEV is active, then an IA32 PEI phase is
>> simply unusable. Silently pretending that the TPM is not there, even
>> though it may have been configured on the QEMU command line, we just
>> failed to communicate with it, is not a good idea, IMO.
> 
> However, because the c-bit is not part of the NPF, we do communicate
> successfully with the TPM.
> 
> So we could actually do following:
>  - For IA32:
>    - Remove the Depex on gOvmfTpmMmioAccessiblePpiGuid
>    - Do not add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
> 
>  - For X64:
>    - Add the Depex on gOvmfTpmMmioAccessiblePpiGuid
>    - Add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
> 
> That might be confusing, though. So we could just do option #3 below.
> 
> Thanks,
> Tom
> 
>>
>> This is somewhat similar IMO to the S3Verification() function in
>> "OvmfPkg/PlatformPei/Platform.c".
>>
>> TPM_ENABLE, SEV, IA32 PEI phase: pick any two.
>>
>> Thanks,
>> Laszlo
>>
>>>
>>> 2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
>>>    the return status.
>>>
>>> 3. Create Ia32 and X64 versions of internal functions, where the Ia32
>>>    version simply returns SUCCESS because it can't do anything and the X64
>>>    version calls MemEncryptSevClearPageEncMask(), allowing the main code
>>>    to ASSERT on any errors.
>>>
>>> I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?
>>>
>>> Thanks,
>>> Tom
>>>
>>>>
>>>> One thing I found is that the Bhyve package makes reference to the
>>>> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
>>>> think that TPM enablement has been tested. I didn't update the Bhyve
>>>> support for that reason.
>>>>
>>>> Thanks,
>>>> Tom
>>>>
>>>>> Thanks!
>>>>> Laszlo
>>>>>
>>>
>>


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

On 04/27/21 16:58, Tom Lendacky wrote:
> On 4/26/21 9:21 AM, Tom Lendacky wrote:
>> On 4/26/21 7:07 AM, Laszlo Ersek wrote:
>>> On 04/23/21 22:02, Tom Lendacky wrote:

>>>> 1. SEV works with the current encrypted mapping, it is only the SEV-ES
>>>>    support that fails because of the ValidateMmioMemory() check. I can do
>>>>    the mapping change just for SEV-ES since it is X64 only. This works,
>>>>    because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
>>>>    when running in 64-bit.
>>>
>>> Can we really say "SEV works" though? Because, even using an X64 PEI
>>> phase, and enabling only SEV (not SEV-ES), TPM access will be broken in
>>> the PEI phase. Is my understanding correct?
>>
>> Because the memory range is marked as MMIO, we'll take a nested page fault
>> (NPF). The GPA passed as part of the NPF does not include the c-bit. So we
>> do in fact work properly with a TPM in SEV.

Thanks for the explanation.

Here's what bothers me about it:

In AmdSevDxe, we clear the C-bit from MMIO and NonExistent areas in the
GCD memory space map. This occurs early in the DXE phase (see "APRIORI
DXE" in the FDF files). The justification is that we want the flash and
(for example) the PCI MMIO apertures decrypted.

Now, I realize there is a difference between flash and TPM. TPM is
purely MMIO (no KVM memslot), but flash (when it is not in programming
mode) is backed by a read-only KVM memslot. IOW, flash is "actual
memory", and so it is affected by SEV. TPM is never "actual memory", so
(according to your explanation, AIUI) it always traps to QEMU, per
access, and the C-bit doesn't interfere with that.

This is consistent with two facts about OVMF's PEI phase:

- We use IO Port-based fw_cfg (never DMA), if SEV is enabled (see
"QemuFwCfgPei.c").

- We access PCI config space via IO Ports (0xCF8, 0xCFC), never ECAM.
(This was not motivated by SEV, see commit 7523788faa51, but it does
play nice with SEV, in the PEI phase -- I think?)

What I'm confused about, now, in retrospect, is the reference to the PCI
MMIO aperture, in AmdSevDxe. If that area isn't backed by a KVM memslot
*either* -- similarly to the TPM area --, then decrypting *that* in
AmdSevDxe (via "nonexistent") is not strictly necessary. Is that correct?

I'm not asking for any code changes, just trying to form a consistent view.

Another question (still for "base SEV"): when OVMF is built with
SMM_REQUIRE, PlatformPei performs a (read-only) variable access. See the
ReadOnlyVariable2->GetVariable() call in the RefreshMemTypeInfo()
function. When SEV is active, does control reach RefreshMemTypeInfo() on
your end? And does ReadOnlyVariable2->GetVariable() succeed for you?

(There is a DEBUG_VERBOSE message in OnReadOnlyVariable2Available(), and
a DEBUG_ERROR in RefreshMemTypeInfo(), so the above questions can be
answered just from the log; no need to modify the code for that.)

Basically, with SEV enabled, I expect ReadOnlyVariable2->GetVariable()
to fail -- or even to remain unreached, as FaultTolerantWritePei and
VariablePei could bail out earlier (before installing the Variable PPI),
due to failing flash accesses. In case I'm *not* wrong -- it's not the
end of the world, I'm only asking this question too for the sake of
clarifying "C-bit vs. MMIO".

More or less it seems to boil down to whether there is a KVM memslot or
not -- which is *not* equivalent to OVMF considering the area MMIO or not.


>> SEV-ES would also work
>> properly if the mitigation for accessing an encrypted address was removed
>> from the #VC handler. It is only this added mitigation to protect MMIO
>> that results in an issue with the TPM in PEI.
> 
> So I'm thinking that I can have TpmMmioSevDecryptPeim.c do this:
> 
>   //
>   // If SEV or SEV-ES is active, MMIO succeeds against an encrypted physical
>   // address because the nested page fault (NPF) that occurs on access does not
>   // include the encryption bit in the guest physical address provided to the
>   // hypervisor.
>   //
>   // However, if SEV-ES is active, before performing the actual MMIO, an
>   // additional MMIO mitigation check is performed in the #VC handler to ensure
>   // that MMIO is being done to an unencrypted address. To prevent guest
>   // termination in this scenario, mark the range unencrypted ahead of access.
>   //
>   if (MemEncryptSevEsIsEnabled ()) {
>     // Do MemEncryptSevClearPageEncMask() ...
>   }
> 
> Let me submit the next version with this and see what you think.

Yep, I'll review that now.

Thanks
Laszlo

> 
> Thanks,
> Tom
> 
>>
>>>
>>> I think the behavior you currently see is actually what we want, we
>>> should double down on it -- if MemEncryptSevClearPageEncMask() fails,
>>> report an explicit DEBUG_ERROR, and call CpuDeadLoop(). If the firmware
>>> is built with TPM_ENABLE, and SEV is active, then an IA32 PEI phase is
>>> simply unusable. Silently pretending that the TPM is not there, even
>>> though it may have been configured on the QEMU command line, we just
>>> failed to communicate with it, is not a good idea, IMO.
>>
>> However, because the c-bit is not part of the NPF, we do communicate
>> successfully with the TPM.
>>
>> So we could actually do following:
>>  - For IA32:
>>    - Remove the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>    - Do not add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>
>>  - For X64:
>>    - Add the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>    - Add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>
>> That might be confusing, though. So we could just do option #3 below.
>>
>> Thanks,
>> Tom
>>
>>>
>>> This is somewhat similar IMO to the S3Verification() function in
>>> "OvmfPkg/PlatformPei/Platform.c".
>>>
>>> TPM_ENABLE, SEV, IA32 PEI phase: pick any two.
>>>
>>> Thanks,
>>> Laszlo
>>>
>>>>
>>>> 2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
>>>>    the return status.
>>>>
>>>> 3. Create Ia32 and X64 versions of internal functions, where the Ia32
>>>>    version simply returns SUCCESS because it can't do anything and the X64
>>>>    version calls MemEncryptSevClearPageEncMask(), allowing the main code
>>>>    to ASSERT on any errors.
>>>>
>>>> I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?
>>>>
>>>> Thanks,
>>>> Tom
>>>>
>>>>>
>>>>> One thing I found is that the Bhyve package makes reference to the
>>>>> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
>>>>> think that TPM enablement has been tested. I didn't update the Bhyve
>>>>> support for that reason.
>>>>>
>>>>> Thanks,
>>>>> Tom
>>>>>
>>>>>> Thanks!
>>>>>> Laszlo
>>>>>>
>>>>
>>>
> 



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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Lendacky, Thomas 4 years, 9 months ago

On 4/28/21 11:12 AM, Laszlo Ersek wrote:
> On 04/27/21 16:58, Tom Lendacky wrote:
>> On 4/26/21 9:21 AM, Tom Lendacky wrote:
>>> On 4/26/21 7:07 AM, Laszlo Ersek wrote:
>>>> On 04/23/21 22:02, Tom Lendacky wrote:
> 
>>>>> 1. SEV works with the current encrypted mapping, it is only the SEV-ES
>>>>>    support that fails because of the ValidateMmioMemory() check. I can do
>>>>>    the mapping change just for SEV-ES since it is X64 only. This works,
>>>>>    because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
>>>>>    when running in 64-bit.
>>>>
>>>> Can we really say "SEV works" though? Because, even using an X64 PEI
>>>> phase, and enabling only SEV (not SEV-ES), TPM access will be broken in
>>>> the PEI phase. Is my understanding correct?
>>>
>>> Because the memory range is marked as MMIO, we'll take a nested page fault
>>> (NPF). The GPA passed as part of the NPF does not include the c-bit. So we
>>> do in fact work properly with a TPM in SEV.
> 
> Thanks for the explanation.
> 
> Here's what bothers me about it:
> 
> In AmdSevDxe, we clear the C-bit from MMIO and NonExistent areas in the
> GCD memory space map. This occurs early in the DXE phase (see "APRIORI
> DXE" in the FDF files). The justification is that we want the flash and
> (for example) the PCI MMIO apertures decrypted.
> 
> Now, I realize there is a difference between flash and TPM. TPM is
> purely MMIO (no KVM memslot), but flash (when it is not in programming
> mode) is backed by a read-only KVM memslot. IOW, flash is "actual
> memory", and so it is affected by SEV. TPM is never "actual memory", so
> (according to your explanation, AIUI) it always traps to QEMU, per
> access, and the C-bit doesn't interfere with that.
> 
> This is consistent with two facts about OVMF's PEI phase:
> 
> - We use IO Port-based fw_cfg (never DMA), if SEV is enabled (see
> "QemuFwCfgPei.c").
> 
> - We access PCI config space via IO Ports (0xCF8, 0xCFC), never ECAM.
> (This was not motivated by SEV, see commit 7523788faa51, but it does
> play nice with SEV, in the PEI phase -- I think?)
> 
> What I'm confused about, now, in retrospect, is the reference to the PCI
> MMIO aperture, in AmdSevDxe. If that area isn't backed by a KVM memslot
> *either* -- similarly to the TPM area --, then decrypting *that* in
> AmdSevDxe (via "nonexistent") is not strictly necessary. Is that correct?

It is necessary for (and was added for) SEV-ES. The explicit mapping of
the PCI MMCONFIG range as unencrypted was added for SEV-ES so that the
SEV-ES mitigation would not terminate the guest because MMIO was being
performed against an encrypted address.

There's a nice comment in OvmfPkg/PlatformPei/Platform.c that talks about
how the MMCONFIG range is not added as MMIO, but instead as reserved
memory. Because of that, the loop through the memory space map in
AmdSevDxe.c does not mark the MMCONFIG range as unencrypted.

> 
> I'm not asking for any code changes, just trying to form a consistent view.
> 
> Another question (still for "base SEV"): when OVMF is built with
> SMM_REQUIRE, PlatformPei performs a (read-only) variable access. See the
> ReadOnlyVariable2->GetVariable() call in the RefreshMemTypeInfo()
> function. When SEV is active, does control reach RefreshMemTypeInfo() on
> your end? And does ReadOnlyVariable2->GetVariable() succeed for you?
> 
> (There is a DEBUG_VERBOSE message in OnReadOnlyVariable2Available(), and
> a DEBUG_ERROR in RefreshMemTypeInfo(), so the above questions can be
> answered just from the log; no need to modify the code for that.)

Yes, control reaches that point. But, notably, with a legacy VM I see the
following messages:
  RefreshMemTypeInfo: GetVariable(): Not Found

But with an SEV VM I see:
  Firmware Volume for Variable Store is corrupted
  RefreshMemTypeInfo: GetVariable(): Not Found

So I get the "Not Found" in both cases. But with SEV, I see the
"corrupted" message from InitRealNonVolatileVariableStore() in
MdeModulePkg/Universal/Variable/RuntimeDxe/VariableNonVolatile.c. I
imagine that since the range is marked encrypted, it reads the header
incorrectly and fails.

Thanks,
Tom

> 
> Basically, with SEV enabled, I expect ReadOnlyVariable2->GetVariable()
> to fail -- or even to remain unreached, as FaultTolerantWritePei and
> VariablePei could bail out earlier (before installing the Variable PPI),
> due to failing flash accesses. In case I'm *not* wrong -- it's not the
> end of the world, I'm only asking this question too for the sake of
> clarifying "C-bit vs. MMIO".
> 
> More or less it seems to boil down to whether there is a KVM memslot or
> not -- which is *not* equivalent to OVMF considering the area MMIO or not.
> 
> 
>>> SEV-ES would also work
>>> properly if the mitigation for accessing an encrypted address was removed
>>> from the #VC handler. It is only this added mitigation to protect MMIO
>>> that results in an issue with the TPM in PEI.
>>
>> So I'm thinking that I can have TpmMmioSevDecryptPeim.c do this:
>>
>>   //
>>   // If SEV or SEV-ES is active, MMIO succeeds against an encrypted physical
>>   // address because the nested page fault (NPF) that occurs on access does not
>>   // include the encryption bit in the guest physical address provided to the
>>   // hypervisor.
>>   //
>>   // However, if SEV-ES is active, before performing the actual MMIO, an
>>   // additional MMIO mitigation check is performed in the #VC handler to ensure
>>   // that MMIO is being done to an unencrypted address. To prevent guest
>>   // termination in this scenario, mark the range unencrypted ahead of access.
>>   //
>>   if (MemEncryptSevEsIsEnabled ()) {
>>     // Do MemEncryptSevClearPageEncMask() ...
>>   }
>>
>> Let me submit the next version with this and see what you think.
> 
> Yep, I'll review that now.
> 
> Thanks
> Laszlo
> 
>>
>> Thanks,
>> Tom
>>
>>>
>>>>
>>>> I think the behavior you currently see is actually what we want, we
>>>> should double down on it -- if MemEncryptSevClearPageEncMask() fails,
>>>> report an explicit DEBUG_ERROR, and call CpuDeadLoop(). If the firmware
>>>> is built with TPM_ENABLE, and SEV is active, then an IA32 PEI phase is
>>>> simply unusable. Silently pretending that the TPM is not there, even
>>>> though it may have been configured on the QEMU command line, we just
>>>> failed to communicate with it, is not a good idea, IMO.
>>>
>>> However, because the c-bit is not part of the NPF, we do communicate
>>> successfully with the TPM.
>>>
>>> So we could actually do following:
>>>  - For IA32:
>>>    - Remove the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>>    - Do not add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>>
>>>  - For X64:
>>>    - Add the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>>    - Add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>>
>>> That might be confusing, though. So we could just do option #3 below.
>>>
>>> Thanks,
>>> Tom
>>>
>>>>
>>>> This is somewhat similar IMO to the S3Verification() function in
>>>> "OvmfPkg/PlatformPei/Platform.c".
>>>>
>>>> TPM_ENABLE, SEV, IA32 PEI phase: pick any two.
>>>>
>>>> Thanks,
>>>> Laszlo
>>>>
>>>>>
>>>>> 2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
>>>>>    the return status.
>>>>>
>>>>> 3. Create Ia32 and X64 versions of internal functions, where the Ia32
>>>>>    version simply returns SUCCESS because it can't do anything and the X64
>>>>>    version calls MemEncryptSevClearPageEncMask(), allowing the main code
>>>>>    to ASSERT on any errors.
>>>>>
>>>>> I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?
>>>>>
>>>>> Thanks,
>>>>> Tom
>>>>>
>>>>>>
>>>>>> One thing I found is that the Bhyve package makes reference to the
>>>>>> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
>>>>>> think that TPM enablement has been tested. I didn't update the Bhyve
>>>>>> support for that reason.
>>>>>>
>>>>>> Thanks,
>>>>>> Tom
>>>>>>
>>>>>>> Thanks!
>>>>>>> Laszlo
>>>>>>>
>>>>>
>>>>
>>
> 


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

On 04/28/21 21:09, Tom Lendacky wrote:
> On 4/28/21 11:12 AM, Laszlo Ersek wrote:
>> On 04/27/21 16:58, Tom Lendacky wrote:
>>> On 4/26/21 9:21 AM, Tom Lendacky wrote:
>>>> On 4/26/21 7:07 AM, Laszlo Ersek wrote:
>>>>> On 04/23/21 22:02, Tom Lendacky wrote:
>>
>>>>>> 1. SEV works with the current encrypted mapping, it is only the SEV-ES
>>>>>>    support that fails because of the ValidateMmioMemory() check. I can do
>>>>>>    the mapping change just for SEV-ES since it is X64 only. This works,
>>>>>>    because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
>>>>>>    when running in 64-bit.
>>>>>
>>>>> Can we really say "SEV works" though? Because, even using an X64 PEI
>>>>> phase, and enabling only SEV (not SEV-ES), TPM access will be broken in
>>>>> the PEI phase. Is my understanding correct?
>>>>
>>>> Because the memory range is marked as MMIO, we'll take a nested page fault
>>>> (NPF). The GPA passed as part of the NPF does not include the c-bit. So we
>>>> do in fact work properly with a TPM in SEV.
>>
>> Thanks for the explanation.
>>
>> Here's what bothers me about it:
>>
>> In AmdSevDxe, we clear the C-bit from MMIO and NonExistent areas in the
>> GCD memory space map. This occurs early in the DXE phase (see "APRIORI
>> DXE" in the FDF files). The justification is that we want the flash and
>> (for example) the PCI MMIO apertures decrypted.
>>
>> Now, I realize there is a difference between flash and TPM. TPM is
>> purely MMIO (no KVM memslot), but flash (when it is not in programming
>> mode) is backed by a read-only KVM memslot. IOW, flash is "actual
>> memory", and so it is affected by SEV. TPM is never "actual memory", so
>> (according to your explanation, AIUI) it always traps to QEMU, per
>> access, and the C-bit doesn't interfere with that.
>>
>> This is consistent with two facts about OVMF's PEI phase:
>>
>> - We use IO Port-based fw_cfg (never DMA), if SEV is enabled (see
>> "QemuFwCfgPei.c").
>>
>> - We access PCI config space via IO Ports (0xCF8, 0xCFC), never ECAM.
>> (This was not motivated by SEV, see commit 7523788faa51, but it does
>> play nice with SEV, in the PEI phase -- I think?)
>>
>> What I'm confused about, now, in retrospect, is the reference to the PCI
>> MMIO aperture, in AmdSevDxe. If that area isn't backed by a KVM memslot
>> *either* -- similarly to the TPM area --, then decrypting *that* in
>> AmdSevDxe (via "nonexistent") is not strictly necessary. Is that correct?
> 
> It is necessary for (and was added for) SEV-ES. The explicit mapping of
> the PCI MMCONFIG range as unencrypted was added for SEV-ES so that the
> SEV-ES mitigation would not terminate the guest because MMIO was being
> performed against an encrypted address.
> 
> There's a nice comment in OvmfPkg/PlatformPei/Platform.c that talks about
> how the MMCONFIG range is not added as MMIO, but instead as reserved
> memory. Because of that, the loop through the memory space map in
> AmdSevDxe.c does not mark the MMCONFIG range as unencrypted.

I didn't mean commit 84cddd70820f ("OvmfPkg/AmdSevDxe: Clear encryption
bit on PCIe MMCONFIG range", 2021-01-07) -- I didn't mean PCI config space.

I meant commit 24e4ad75546b ("OvmfPkg: Add AmdSevDxe driver",
2017-07-10) -- I wrote "PCI MMIO aperture".

So, to repeat my question: when 24e4ad75546b3 was implemented (which
happened just for SEV), then (apparently) clearing the C-bit on the PCI
MMIO aperture (where PCI MMIO BARs were going to be allocated from)
wasn't strictly necessary *at the time*; correct? Because that area
isn't backed by RAM, accesses trap to QEMU directly, and the C bit does
not make a difference there. (IIUC). Does this make sense or am I wrong?


> 
>>
>> I'm not asking for any code changes, just trying to form a consistent view.
>>
>> Another question (still for "base SEV"): when OVMF is built with
>> SMM_REQUIRE, PlatformPei performs a (read-only) variable access. See the
>> ReadOnlyVariable2->GetVariable() call in the RefreshMemTypeInfo()
>> function. When SEV is active, does control reach RefreshMemTypeInfo() on
>> your end? And does ReadOnlyVariable2->GetVariable() succeed for you?
>>
>> (There is a DEBUG_VERBOSE message in OnReadOnlyVariable2Available(), and
>> a DEBUG_ERROR in RefreshMemTypeInfo(), so the above questions can be
>> answered just from the log; no need to modify the code for that.)
> 
> Yes, control reaches that point. But, notably, with a legacy VM I see the
> following messages:
>   RefreshMemTypeInfo: GetVariable(): Not Found
> 
> But with an SEV VM I see:
>   Firmware Volume for Variable Store is corrupted
>   RefreshMemTypeInfo: GetVariable(): Not Found
> 
> So I get the "Not Found" in both cases. But with SEV, I see the
> "corrupted" message from InitRealNonVolatileVariableStore() in
> MdeModulePkg/Universal/Variable/RuntimeDxe/VariableNonVolatile.c. I
> imagine that since the range is marked encrypted, it reads the header
> incorrectly and fails.

Thank you for confirming! I don't think we need to sweat this symptom.
I'm just glad my hunch wasn't wrong.

Thanks,
Laszlo

> 
> Thanks,
> Tom
> 
>>
>> Basically, with SEV enabled, I expect ReadOnlyVariable2->GetVariable()
>> to fail -- or even to remain unreached, as FaultTolerantWritePei and
>> VariablePei could bail out earlier (before installing the Variable PPI),
>> due to failing flash accesses. In case I'm *not* wrong -- it's not the
>> end of the world, I'm only asking this question too for the sake of
>> clarifying "C-bit vs. MMIO".
>>
>> More or less it seems to boil down to whether there is a KVM memslot or
>> not -- which is *not* equivalent to OVMF considering the area MMIO or not.
>>
>>
>>>> SEV-ES would also work
>>>> properly if the mitigation for accessing an encrypted address was removed
>>>> from the #VC handler. It is only this added mitigation to protect MMIO
>>>> that results in an issue with the TPM in PEI.
>>>
>>> So I'm thinking that I can have TpmMmioSevDecryptPeim.c do this:
>>>
>>>   //
>>>   // If SEV or SEV-ES is active, MMIO succeeds against an encrypted physical
>>>   // address because the nested page fault (NPF) that occurs on access does not
>>>   // include the encryption bit in the guest physical address provided to the
>>>   // hypervisor.
>>>   //
>>>   // However, if SEV-ES is active, before performing the actual MMIO, an
>>>   // additional MMIO mitigation check is performed in the #VC handler to ensure
>>>   // that MMIO is being done to an unencrypted address. To prevent guest
>>>   // termination in this scenario, mark the range unencrypted ahead of access.
>>>   //
>>>   if (MemEncryptSevEsIsEnabled ()) {
>>>     // Do MemEncryptSevClearPageEncMask() ...
>>>   }
>>>
>>> Let me submit the next version with this and see what you think.
>>
>> Yep, I'll review that now.
>>
>> Thanks
>> Laszlo
>>
>>>
>>> Thanks,
>>> Tom
>>>
>>>>
>>>>>
>>>>> I think the behavior you currently see is actually what we want, we
>>>>> should double down on it -- if MemEncryptSevClearPageEncMask() fails,
>>>>> report an explicit DEBUG_ERROR, and call CpuDeadLoop(). If the firmware
>>>>> is built with TPM_ENABLE, and SEV is active, then an IA32 PEI phase is
>>>>> simply unusable. Silently pretending that the TPM is not there, even
>>>>> though it may have been configured on the QEMU command line, we just
>>>>> failed to communicate with it, is not a good idea, IMO.
>>>>
>>>> However, because the c-bit is not part of the NPF, we do communicate
>>>> successfully with the TPM.
>>>>
>>>> So we could actually do following:
>>>>  - For IA32:
>>>>    - Remove the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>>>    - Do not add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>>>
>>>>  - For X64:
>>>>    - Add the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>>>    - Add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>>>
>>>> That might be confusing, though. So we could just do option #3 below.
>>>>
>>>> Thanks,
>>>> Tom
>>>>
>>>>>
>>>>> This is somewhat similar IMO to the S3Verification() function in
>>>>> "OvmfPkg/PlatformPei/Platform.c".
>>>>>
>>>>> TPM_ENABLE, SEV, IA32 PEI phase: pick any two.
>>>>>
>>>>> Thanks,
>>>>> Laszlo
>>>>>
>>>>>>
>>>>>> 2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
>>>>>>    the return status.
>>>>>>
>>>>>> 3. Create Ia32 and X64 versions of internal functions, where the Ia32
>>>>>>    version simply returns SUCCESS because it can't do anything and the X64
>>>>>>    version calls MemEncryptSevClearPageEncMask(), allowing the main code
>>>>>>    to ASSERT on any errors.
>>>>>>
>>>>>> I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?
>>>>>>
>>>>>> Thanks,
>>>>>> Tom
>>>>>>
>>>>>>>
>>>>>>> One thing I found is that the Bhyve package makes reference to the
>>>>>>> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
>>>>>>> think that TPM enablement has been tested. I didn't update the Bhyve
>>>>>>> support for that reason.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Tom
>>>>>>>
>>>>>>>> Thanks!
>>>>>>>> Laszlo
>>>>>>>>
>>>>>>
>>>>>
>>>
>>
> 



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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Lendacky, Thomas 4 years, 9 months ago

On 4/30/21 10:39 AM, Laszlo Ersek wrote:
> On 04/28/21 21:09, Tom Lendacky wrote:
>> On 4/28/21 11:12 AM, Laszlo Ersek wrote:
>>> On 04/27/21 16:58, Tom Lendacky wrote:
>>>> On 4/26/21 9:21 AM, Tom Lendacky wrote:
>>>>> On 4/26/21 7:07 AM, Laszlo Ersek wrote:
>>>>>> On 04/23/21 22:02, Tom Lendacky wrote:
>>>
>>>>>>> 1. SEV works with the current encrypted mapping, it is only the SEV-ES
>>>>>>>    support that fails because of the ValidateMmioMemory() check. I can do
>>>>>>>    the mapping change just for SEV-ES since it is X64 only. This works,
>>>>>>>    because MemEncryptSevClearPageEncMask() will not return UNSUPPORTED
>>>>>>>    when running in 64-bit.
>>>>>>
>>>>>> Can we really say "SEV works" though? Because, even using an X64 PEI
>>>>>> phase, and enabling only SEV (not SEV-ES), TPM access will be broken in
>>>>>> the PEI phase. Is my understanding correct?
>>>>>
>>>>> Because the memory range is marked as MMIO, we'll take a nested page fault
>>>>> (NPF). The GPA passed as part of the NPF does not include the c-bit. So we
>>>>> do in fact work properly with a TPM in SEV.
>>>
>>> Thanks for the explanation.
>>>
>>> Here's what bothers me about it:
>>>
>>> In AmdSevDxe, we clear the C-bit from MMIO and NonExistent areas in the
>>> GCD memory space map. This occurs early in the DXE phase (see "APRIORI
>>> DXE" in the FDF files). The justification is that we want the flash and
>>> (for example) the PCI MMIO apertures decrypted.
>>>
>>> Now, I realize there is a difference between flash and TPM. TPM is
>>> purely MMIO (no KVM memslot), but flash (when it is not in programming
>>> mode) is backed by a read-only KVM memslot. IOW, flash is "actual
>>> memory", and so it is affected by SEV. TPM is never "actual memory", so
>>> (according to your explanation, AIUI) it always traps to QEMU, per
>>> access, and the C-bit doesn't interfere with that.
>>>
>>> This is consistent with two facts about OVMF's PEI phase:
>>>
>>> - We use IO Port-based fw_cfg (never DMA), if SEV is enabled (see
>>> "QemuFwCfgPei.c").
>>>
>>> - We access PCI config space via IO Ports (0xCF8, 0xCFC), never ECAM.
>>> (This was not motivated by SEV, see commit 7523788faa51, but it does
>>> play nice with SEV, in the PEI phase -- I think?)
>>>
>>> What I'm confused about, now, in retrospect, is the reference to the PCI
>>> MMIO aperture, in AmdSevDxe. If that area isn't backed by a KVM memslot
>>> *either* -- similarly to the TPM area --, then decrypting *that* in
>>> AmdSevDxe (via "nonexistent") is not strictly necessary. Is that correct?
>>
>> It is necessary for (and was added for) SEV-ES. The explicit mapping of
>> the PCI MMCONFIG range as unencrypted was added for SEV-ES so that the
>> SEV-ES mitigation would not terminate the guest because MMIO was being
>> performed against an encrypted address.
>>
>> There's a nice comment in OvmfPkg/PlatformPei/Platform.c that talks about
>> how the MMCONFIG range is not added as MMIO, but instead as reserved
>> memory. Because of that, the loop through the memory space map in
>> AmdSevDxe.c does not mark the MMCONFIG range as unencrypted.
> 
> I didn't mean commit 84cddd70820f ("OvmfPkg/AmdSevDxe: Clear encryption
> bit on PCIe MMCONFIG range", 2021-01-07) -- I didn't mean PCI config space.
> 
> I meant commit 24e4ad75546b ("OvmfPkg: Add AmdSevDxe driver",
> 2017-07-10) -- I wrote "PCI MMIO aperture".
> 
> So, to repeat my question: when 24e4ad75546b3 was implemented (which
> happened just for SEV), then (apparently) clearing the C-bit on the PCI
> MMIO aperture (where PCI MMIO BARs were going to be allocated from)
> wasn't strictly necessary *at the time*; correct? Because that area
> isn't backed by RAM, accesses trap to QEMU directly, and the C bit does
> not make a difference there. (IIUC). Does this make sense or am I wrong?

Ah, sorry, I misunderstood. For the most part, that is true. Not clearing
the c-bit from an area where the PCI MMIO BARs are going to be allocated
would not necessarily cause a problem.

However, clearing the c-bit for non-existent areas was needed for other
reasons. It would result in NVRAM variable corruption because of the way
that area is represented in OVMF and how it is mapped by the hypervisor.

For example, if the clearing of the c-bit for the address at 0xfef00000,
which is marked as EfiGcdMemoryTypeNonExistent, isn't done, then using the
same nvram FD file in an SEV guest results in the following:

  Variable FV header is not valid. It will be reinitialized.

because a different encryption key is used on each launch of the guest.

And attempting to use the same nvram FD file for a non-SEV guest, after
running as an SEV guest, causes an ASSERT:

  ASSERT [VariableRuntimeDxe] /root/kernels/ovmf-build-X64/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableNonVolatile.c(218): VariableStore->Size == VariableStoreLength

because the contents have been encrypted.

The video buffer suffers from a similar problem in that the video buffer
contents end up containing data that appears encrypted to the hypervisor
and results in corruption of the screen contents when attaching, e.g.,
via VNC. Although, that area is marked as EfiGcdMemoryTypeMemoryMappedIo.

Thanks,
Tom

> 
> 
>>
>>>
>>> I'm not asking for any code changes, just trying to form a consistent view.
>>>
>>> Another question (still for "base SEV"): when OVMF is built with
>>> SMM_REQUIRE, PlatformPei performs a (read-only) variable access. See the
>>> ReadOnlyVariable2->GetVariable() call in the RefreshMemTypeInfo()
>>> function. When SEV is active, does control reach RefreshMemTypeInfo() on
>>> your end? And does ReadOnlyVariable2->GetVariable() succeed for you?
>>>
>>> (There is a DEBUG_VERBOSE message in OnReadOnlyVariable2Available(), and
>>> a DEBUG_ERROR in RefreshMemTypeInfo(), so the above questions can be
>>> answered just from the log; no need to modify the code for that.)
>>
>> Yes, control reaches that point. But, notably, with a legacy VM I see the
>> following messages:
>>   RefreshMemTypeInfo: GetVariable(): Not Found
>>
>> But with an SEV VM I see:
>>   Firmware Volume for Variable Store is corrupted
>>   RefreshMemTypeInfo: GetVariable(): Not Found
>>
>> So I get the "Not Found" in both cases. But with SEV, I see the
>> "corrupted" message from InitRealNonVolatileVariableStore() in
>> MdeModulePkg/Universal/Variable/RuntimeDxe/VariableNonVolatile.c. I
>> imagine that since the range is marked encrypted, it reads the header
>> incorrectly and fails.
> 
> Thank you for confirming! I don't think we need to sweat this symptom.
> I'm just glad my hunch wasn't wrong.
> 
> Thanks,
> Laszlo
> 
>>
>> Thanks,
>> Tom
>>
>>>
>>> Basically, with SEV enabled, I expect ReadOnlyVariable2->GetVariable()
>>> to fail -- or even to remain unreached, as FaultTolerantWritePei and
>>> VariablePei could bail out earlier (before installing the Variable PPI),
>>> due to failing flash accesses. In case I'm *not* wrong -- it's not the
>>> end of the world, I'm only asking this question too for the sake of
>>> clarifying "C-bit vs. MMIO".
>>>
>>> More or less it seems to boil down to whether there is a KVM memslot or
>>> not -- which is *not* equivalent to OVMF considering the area MMIO or not.
>>>
>>>
>>>>> SEV-ES would also work
>>>>> properly if the mitigation for accessing an encrypted address was removed
>>>>> from the #VC handler. It is only this added mitigation to protect MMIO
>>>>> that results in an issue with the TPM in PEI.
>>>>
>>>> So I'm thinking that I can have TpmMmioSevDecryptPeim.c do this:
>>>>
>>>>   //
>>>>   // If SEV or SEV-ES is active, MMIO succeeds against an encrypted physical
>>>>   // address because the nested page fault (NPF) that occurs on access does not
>>>>   // include the encryption bit in the guest physical address provided to the
>>>>   // hypervisor.
>>>>   //
>>>>   // However, if SEV-ES is active, before performing the actual MMIO, an
>>>>   // additional MMIO mitigation check is performed in the #VC handler to ensure
>>>>   // that MMIO is being done to an unencrypted address. To prevent guest
>>>>   // termination in this scenario, mark the range unencrypted ahead of access.
>>>>   //
>>>>   if (MemEncryptSevEsIsEnabled ()) {
>>>>     // Do MemEncryptSevClearPageEncMask() ...
>>>>   }
>>>>
>>>> Let me submit the next version with this and see what you think.
>>>
>>> Yep, I'll review that now.
>>>
>>> Thanks
>>> Laszlo
>>>
>>>>
>>>> Thanks,
>>>> Tom
>>>>
>>>>>
>>>>>>
>>>>>> I think the behavior you currently see is actually what we want, we
>>>>>> should double down on it -- if MemEncryptSevClearPageEncMask() fails,
>>>>>> report an explicit DEBUG_ERROR, and call CpuDeadLoop(). If the firmware
>>>>>> is built with TPM_ENABLE, and SEV is active, then an IA32 PEI phase is
>>>>>> simply unusable. Silently pretending that the TPM is not there, even
>>>>>> though it may have been configured on the QEMU command line, we just
>>>>>> failed to communicate with it, is not a good idea, IMO.
>>>>>
>>>>> However, because the c-bit is not part of the NPF, we do communicate
>>>>> successfully with the TPM.
>>>>>
>>>>> So we could actually do following:
>>>>>  - For IA32:
>>>>>    - Remove the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>>>>    - Do not add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>>>>
>>>>>  - For X64:
>>>>>    - Add the Depex on gOvmfTpmMmioAccessiblePpiGuid
>>>>>    - Add OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>>>>>
>>>>> That might be confusing, though. So we could just do option #3 below.
>>>>>
>>>>> Thanks,
>>>>> Tom
>>>>>
>>>>>>
>>>>>> This is somewhat similar IMO to the S3Verification() function in
>>>>>> "OvmfPkg/PlatformPei/Platform.c".
>>>>>>
>>>>>> TPM_ENABLE, SEV, IA32 PEI phase: pick any two.
>>>>>>
>>>>>> Thanks,
>>>>>> Laszlo
>>>>>>
>>>>>>>
>>>>>>> 2. Call MemEncryptSevClearPageEncMask() for SEV or SEV-ES, but don't check
>>>>>>>    the return status.
>>>>>>>
>>>>>>> 3. Create Ia32 and X64 versions of internal functions, where the Ia32
>>>>>>>    version simply returns SUCCESS because it can't do anything and the X64
>>>>>>>    version calls MemEncryptSevClearPageEncMask(), allowing the main code
>>>>>>>    to ASSERT on any errors.
>>>>>>>
>>>>>>> I'm leaning towards #1, because this is an SEV-ES only issue. Thoughts?
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Tom
>>>>>>>
>>>>>>>>
>>>>>>>> One thing I found is that the Bhyve package makes reference to the
>>>>>>>> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
>>>>>>>> think that TPM enablement has been tested. I didn't update the Bhyve
>>>>>>>> support for that reason.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Tom
>>>>>>>>
>>>>>>>>> Thanks!
>>>>>>>>> Laszlo
>>>>>>>>>
>>>>>>>
>>>>>>
>>>>
>>>
>>
> 


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Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

Posted by Laszlo Ersek 4 years, 9 months ago

On 04/23/21 19:41, Tom Lendacky wrote:
> On 4/23/21 8:04 AM, Laszlo Ersek wrote:

>> I've had a further idea on this.
>>
>> You could add an entirely new PEIM just for this. The entry point
>> function of the PEIM would check for SEV, decrypt the TPM range if SEV
>> were active, and then install gOvmfTpmMmioAccessiblePpiGuid
>> (unconditionally). The exit status of the PEIM would always be
>> EFI_ABORTED, because there would be no need to keep the PEIM resident.
>>
>> The new PEIM would have a DEPEX on gEfiPeiMemoryDiscoveredPpiGuid, to
>> make sure that potential page table splitting for the potential MMIO
>> range decryption could be satisfied from permanent PEI RAM.
>>
>> The new PEIM would be included in the DSC and FDF files of the usual
>> three OVMF platforms, and in the Bhyve platform -- dependent on the
>> TPM_ENABLE build flag.
>>
>> There are several advantages to such a separate PEIM:
>>
>> - For Bhyve, the update is minimal. Just include one line in each of the
>> FDF and the DSC files. No need to customize an existent
>> platform-specific PEIM, no code duplication between two PlatformPei modules.
>>
>> - The new PEIM would depend on the TPM_ENABLE build flag, so it would
>> only be included in the firmware binaries if and only if Tcg2ConfigPei
>> were. No useless PPI installation would occur in the absence of TPM_ENABLE.
>>
>> - No need to check PcdTpmBaseAddress for nullity in the new PEIM, before
>> the decryption, as TPM_ENABLE guarantees (on IA32/X64) that the PCD
>> already has the right value.
>>
>> - The new logic would be properly ordered between PlatformPei and
>> Tcg2ConfigPei, namely due to the use of two such PPI GUIDs in DEPEXes
>> that actually make sense. PlatformPei -> TPM MMIO decryptor PEIM ordered
>> via "memory discovered" (needed for potential page table splitting), TPM
>> MMIO decryptor PEIM -> Tcg2ConfigPei ordered via "TPM MMIO decrypted".
>>
>> You could place the new PEIM at:
>>
>>   OvmfPkg/Tcg/TpmMmioSevDecryptPei
>>
>> If you haven't lost your patience with me yet, I'd really appreciate if
>> you could investigate this!
>>
> 
> So far, this appears to be working nicely. I'm new at the whole PEIM
> thing, so hopefully I haven't missed anything. I should be submitting the
> patches soon for review.

Thanks!

> 
> One thing I found is that the Bhyve package makes reference to the
> OvmfPkg/Bhyve/Tcg directory, but that directory does not exist. So I don't
> think that TPM enablement has been tested. I didn't update the Bhyve
> support for that reason.

That's good to know; thanks for reporting this. I've turned it now into
a BZ ticket (assigned to Rebecca):

https://bugzilla.tianocore.org/show_bug.cgi?id=3354

Thanks!
Laszlo



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[edk2-devel] [PATCH 1/3] OvfmPkg/VmgExitLib: Properly decode MMIO MOVZX and MOVSX opcodes
[edk2-devel] [PATCH 2/3] OvmfPkg/VmgExitLib: Add support for new MMIO MOV opcodes
[edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV