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contact devel+owner@edk2.groups.io Reply-To: devel@edk2.groups.io,brijesh.singh@amd.com X-Gm-Message-State: bnyDBYEzDUC2bkaoAtmA7FQTx1787277AA= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=groups.io; q=dns/txt; s=20140610; t=1619783551; bh=T31TnJARLNN8WtL4KnKb9otprWn1HhGKlTkmRYIt9r8=; h=Cc:Content-Type:Date:From:Reply-To:Subject:To; b=BXjfzK+75FXdEa+H1s/wiD9+bQ8h0ZBojMoD9+cCIwVNXzF9I0jXlL1mYTulR8ILu8P SgygmDJn8l0+g4a4FV9xGsUtGRcjWInR2OIRRG52TylOQYmQAZ+25zytWd7c+uQJubXoz nHPCmlP+ddeBHGH7NbdeuH/50JmqFyYlCjM= X-ZohoMail-DKIM: pass (identity @groups.io) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3D3275 An SEV-SNP guest requires that private memory (aka pages mapped encrypted) must be validated before being accessed. The validation process consist of the following sequence: 1) Set the memory encryption attribute in the page table (aka C-bit). Note: If the processor is in non-PAE mode, then all the memory accesses are considered private. 2) Add the memory range as private in the RMP table. This can be performed using the Page State Change VMGEXIT defined in the GHCB specification. 3) Use the PVALIDATE instruction to set the Validated Bit in the RMP table. During the guest creation time, the VMM encrypts the OVMF_CODE.fd using the SEV-SNP firmware provided LAUNCH_UPDATE_DATA command. In addition to encrypting the content, the command also validates the memory region. This allows us to execute the code without going through the validation sequence. During execution, the reset vector need to access some data pages (such as page tables, SevESWorkarea, Sec stack). The data pages are accessed as private memory. The data pages are not part of the OVMF_CODE.fd, so they were not validated during the guest creation. There are two approaches we can take to validate the data pages before the access: a) Enhance the OVMF reset vector code to validate the pages as described above (go through step 2 - 3). OR b) Validate the pages during the guest creation time. The SEV firmware provides a command which can be used by the VMM to validate the pages without affecting the measurement of the launch. Approach #b seems much simpler; it does not require any changes to the OVMF reset vector code. Cc: James Bottomley Cc: Min Xu Cc: Jiewen Yao Cc: Tom Lendacky Cc: Jordan Justen Cc: Ard Biesheuvel Cc: Laszlo Ersek Cc: Erdem Aktas Signed-off-by: Brijesh Singh --- OvmfPkg/OvmfPkg.dec | 5 +++++ OvmfPkg/OvmfPkgX64.fdf | 9 ++++++++- OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm | 5 +++++ OvmfPkg/ResetVector/ResetVector.inf | 2 ++ OvmfPkg/ResetVector/ResetVector.nasmb | 2 ++ 5 files changed, 22 insertions(+), 1 deletion(-) diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec index dac5fb1653..3d5574364b 100644 --- a/OvmfPkg/OvmfPkg.dec +++ b/OvmfPkg/OvmfPkg.dec @@ -323,6 +323,11 @@ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpCpuidBase|0x0|UINT32|0x47 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpCpuidSize|0x0|UINT32|0x48 =20 + ## The start and end of pre-validated memory region by the hypervisor + # through the SEV-SNP firmware. + gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedStart|0x0|UIN= T32|0x49 + gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedEnd|0x0|UINT3= 2|0x50 + [PcdsDynamic, PcdsDynamicEx] gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent|0|UINT64|2 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashVariablesEnable|FALSE|BOOLEAN|0x10 diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf index 5cc1da425e..806c86bb3f 100644 --- a/OvmfPkg/OvmfPkgX64.fdf +++ b/OvmfPkg/OvmfPkgX64.fdf @@ -105,7 +105,14 @@ FV =3D PEIFV gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvBase|gUefiOvmfPkgTokenSpaceGuid.= PcdOvmfDxeMemFvSize FV =3D DXEFV =20 -##########################################################################= ###### +##########################################################################= ################ +# +# The range of the pages pre-validated through the SEV-SNP firmware while = creating SEV-SNP guest +# +SET gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedStart =3D $= (MEMFD_BASE_ADDRESS) + gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase + +SET gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedEnd =3D $(M= EMFD_BASE_ADDRESS) + gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase +##########################################################################= ################ =20 [FV.SECFV] FvNameGuid =3D 763BED0D-DE9F-48F5-81F1-3E90E1B1A015 diff --git a/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm b/OvmfPkg/ResetVe= ctor/Ia16/ResetVectorVtf0.asm index 05c7e32f46..769dd0bccf 100644 --- a/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm +++ b/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm @@ -55,11 +55,16 @@ guidedStructureStart: ; the BIOS at a RAM area defined by SEV_SNP_CPUID_BASE. A hypervisor will ; locate this information using the SEV-SNP boot block GUID. ; +; In order to boot the SEV-SNP guest the hypervisor must pre-validated t= he +; memory range from SNP_HV_VALIDATED_START to SNP_HV_VALIDATED_END. +; ; GUID (SEV-SNP boot block): bd39c0c2-2f8e-4243-83e8-1b74cebcb7d9 ; sevSnpBootBlockStart: DD SNP_CPUID_BASE DD SNP_CPUID_SIZE + DD SNP_HV_VALIDATED_START + DD SNP_HV_VALIDATED_END DW sevSnpBootBlockEnd - sevSnpBootBlockStart DB 0xC2, 0xC0, 0x39, 0xBD, 0x8e, 0x2F, 0x43, 0x42 DB 0x83, 0xE8, 0x1B, 0x74, 0xCE, 0xBC, 0xB7, 0xD9 diff --git a/OvmfPkg/ResetVector/ResetVector.inf b/OvmfPkg/ResetVector/Rese= tVector.inf index 8e52265602..2a75e909c7 100644 --- a/OvmfPkg/ResetVector/ResetVector.inf +++ b/OvmfPkg/ResetVector/ResetVector.inf @@ -49,3 +49,5 @@ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpCpuidSize gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize + gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedStart + gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedEnd diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/Re= setVector.nasmb index 57f01aa7c7..f936870b81 100644 --- a/OvmfPkg/ResetVector/ResetVector.nasmb +++ b/OvmfPkg/ResetVector/ResetVector.nasmb @@ -90,5 +90,7 @@ %define SEV_LAUNCH_SECRET_SIZE FixedPcdGet32 (PcdSevLaunchSecretSize) %define SNP_CPUID_BASE FixedPcdGet32 (PcdOvmfSnpCpuidBase) %define SNP_CPUID_SIZE FixedPcdGet32 (PcdOvmfSnpCpuidSize) + %define SNP_HV_VALIDATED_START FixedPcdGet32 (PcdOvmfSnpHypervisorPreVal= idatedStart) + %define SNP_HV_VALIDATED_END FixedPcdGet32 (PcdOvmfSnpHypervisorPreValid= atedEnd) %include "Ia16/ResetVectorVtf0.asm" =20 --=20 2.17.1 -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D- Groups.io Links: You receive all messages sent to this group. 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