To support unregister SMI handler inside SMI handler itself,
get next node before SMI handler is executed, since LIST_ENTRY that
Link points to may be freed if unregister SMI handler in SMI handler
itself.

Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
---
 MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c b/MdeModulePkg/Core/PiSmmCore/Smi.c
index 2985f989c3..a75e52b1ae 100644
--- a/MdeModulePkg/Core/PiSmmCore/Smi.c
+++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
@@ -134,8 +134,14 @@ SmiManage (
 
   Head = &SmiEntry->SmiHandlers;
 
-  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
+  for (Link = Head->ForwardLink; Link != Head;) {
     SmiHandler = CR (Link, SMI_HANDLER, Link, SMI_HANDLER_SIGNATURE);
+    //
+    // To support unregiser SMI handler inside SMI handler itself,
+    // get next node before handler is executed, since LIST_ENTRY that
+    // Link points to may be freed if unregister SMI handler. 
+    //
+    Link = Link->ForwardLink;
 
     Status = SmiHandler->Handler (
                            (EFI_HANDLE)SmiHandler,
-- 
2.31.1.windows.1



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On 1/24/24 05:03, Zhiguang Liu wrote:
> To support unregister SMI handler inside SMI handler itself,
> get next node before SMI handler is executed, since LIST_ENTRY that
> Link points to may be freed if unregister SMI handler in SMI handler
> itself.
> 
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Jiaxin Wu <jiaxin.wu@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
> ---
>  MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c b/MdeModulePkg/Core/PiSmmCore/Smi.c
> index 2985f989c3..a75e52b1ae 100644
> --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
> +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
> @@ -134,8 +134,14 @@ SmiManage (
>  
>    Head = &SmiEntry->SmiHandlers;
>  
> -  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
> +  for (Link = Head->ForwardLink; Link != Head;) {
>      SmiHandler = CR (Link, SMI_HANDLER, Link, SMI_HANDLER_SIGNATURE);
> +    //
> +    // To support unregiser SMI handler inside SMI handler itself,
> +    // get next node before handler is executed, since LIST_ENTRY that
> +    // Link points to may be freed if unregister SMI handler. 
> +    //
> +    Link = Link->ForwardLink;
>  
>      Status = SmiHandler->Handler (
>                             (EFI_HANDLE)SmiHandler,

I've had a further thought here.

(1) This patch may enable an SMI handler to unregister *itself*, that
is, through the following call chain

  SmiManage()
    SmiHandler->Handler()
      SmiHandlerUnRegister()

but it still does not ensure *general iterator safety*.

Assume that an SMM driver registers two handlers, handler A and handler
B. Assume the DispatchHandles for these are stored in global variables
in the driver. Then, assume that "handler A" (for whatever reason, under
some circumstances) unregisters "handler B".

That could still lead to a use-after-free in the SmiManage() loop; is
that right?

If that driver scenario is plausible, then something like the following
would be needed:

- a global variable of enum type in "MdeModulePkg/Core/PiSmmCore/Smi.c",
with three possible values (NotManaging=0, Managing=1, CleanupNeeded=2).

- a new "BOOLEAN Deleted" field in SMI_HANDLER

- all loops in "Smi.c" iterating over SMI_HANDLERs would have to skip
handlers that have been marked as Deleted

- in SmiManage(), set the state to Managing (=1) before the loop. After
the loop, check if the state is CleanupNeeded (=2); if so, add an extra
pass for actually deleting SMI_HANDLERs from the list that have been
marked Deleted. Finally (regardless of the state being Managing (=1) or
CleanupNeeded (=2)), reset the state to NotManaging (=0).

- in SmiHandlerUnRegister(), if the state is NotManaging (=0), delete
the handler immediately. Otherwise (i.e., when the state is Managing
(=1) or CleanupNeeded (=2)), set the state to CleanupNeeded (=2), and
only mark the handler as Deleted.

The idea is to inform SmiHandlerUnRegister() whether it's running or not
running on the stack of SmiManage(), and to postpone SMI_HANDLER
deletion until after the loop finishes in the former case.

I'm not sure if real life SmiHandlerUnRegister() usage is worth this
complication, however.

(2) Independently: does the same issue exist for the StMM core? I seem
to be discovering the same problem in MmiManage()
[StandaloneMmPkg/Core/Mmi.c].

So, whatever patch we add to the SMM_CORE, should likely be reflected to
MM_CORE_STANDALONE too. Adding Ard and Sami to the CC list.

Thanks
Laszlo



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Laszlo,
SMI handler is called from SmmCore.
So SmmCore knows which handle is passed to the SMI handler.
How about let Unregister() rejects the request coming from a SMI handler which unregisters other handles?

A "gCurrentSmiHandle" can be assigned before calling the SMI handler and set to NULL when it returns.
Unregister() compares the handle against gCurrentSmiHandle if it's not NULL.

Thanks,
Ray
> -----Original Message-----
> From: Laszlo Ersek <lersek@redhat.com>
> Sent: Thursday, January 25, 2024 6:48 PM
> To: devel@edk2.groups.io; Liu, Zhiguang <zhiguang.liu@intel.com>
> Cc: Liming Gao <gaoliming@byosoft.com.cn>; Wu, Jiaxin
> <jiaxin.wu@intel.com>; Ni, Ray <ray.ni@intel.com>; Ard Biesheuvel
> <ardb+tianocore@kernel.org>; Sami Mujawar <Sami.Mujawar@arm.com>
> Subject: Re: [edk2-devel] [PATCH] MdeModulePkg/SMM: Support to
> unregister SMI handler inside SMI handler
> 
> On 1/24/24 05:03, Zhiguang Liu wrote:
> > To support unregister SMI handler inside SMI handler itself,
> > get next node before SMI handler is executed, since LIST_ENTRY that
> > Link points to may be freed if unregister SMI handler in SMI handler
> > itself.
> >
> > Cc: Liming Gao <gaoliming@byosoft.com.cn>
> > Cc: Jiaxin Wu <jiaxin.wu@intel.com>
> > Cc: Ray Ni <ray.ni@intel.com>
> > Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
> > ---
> >  MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c
> b/MdeModulePkg/Core/PiSmmCore/Smi.c
> > index 2985f989c3..a75e52b1ae 100644
> > --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
> > +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
> > @@ -134,8 +134,14 @@ SmiManage (
> >
> >    Head = &SmiEntry->SmiHandlers;
> >
> > -  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
> > +  for (Link = Head->ForwardLink; Link != Head;) {
> >      SmiHandler = CR (Link, SMI_HANDLER, Link, SMI_HANDLER_SIGNATURE);
> > +    //
> > +    // To support unregiser SMI handler inside SMI handler itself,
> > +    // get next node before handler is executed, since LIST_ENTRY that
> > +    // Link points to may be freed if unregister SMI handler.
> > +    //
> > +    Link = Link->ForwardLink;
> >
> >      Status = SmiHandler->Handler (
> >                             (EFI_HANDLE)SmiHandler,
> 
> I've had a further thought here.
> 
> (1) This patch may enable an SMI handler to unregister *itself*, that
> is, through the following call chain
> 
>   SmiManage()
>     SmiHandler->Handler()
>       SmiHandlerUnRegister()
> 
> but it still does not ensure *general iterator safety*.
> 
> Assume that an SMM driver registers two handlers, handler A and handler
> B. Assume the DispatchHandles for these are stored in global variables
> in the driver. Then, assume that "handler A" (for whatever reason, under
> some circumstances) unregisters "handler B".
> 
> That could still lead to a use-after-free in the SmiManage() loop; is
> that right?
> 
> If that driver scenario is plausible, then something like the following
> would be needed:
> 
> - a global variable of enum type in "MdeModulePkg/Core/PiSmmCore/Smi.c",
> with three possible values (NotManaging=0, Managing=1, CleanupNeeded=2).
> 
> - a new "BOOLEAN Deleted" field in SMI_HANDLER
> 
> - all loops in "Smi.c" iterating over SMI_HANDLERs would have to skip
> handlers that have been marked as Deleted
> 
> - in SmiManage(), set the state to Managing (=1) before the loop. After
> the loop, check if the state is CleanupNeeded (=2); if so, add an extra
> pass for actually deleting SMI_HANDLERs from the list that have been
> marked Deleted. Finally (regardless of the state being Managing (=1) or
> CleanupNeeded (=2)), reset the state to NotManaging (=0).
> 
> - in SmiHandlerUnRegister(), if the state is NotManaging (=0), delete
> the handler immediately. Otherwise (i.e., when the state is Managing
> (=1) or CleanupNeeded (=2)), set the state to CleanupNeeded (=2), and
> only mark the handler as Deleted.
> 
> The idea is to inform SmiHandlerUnRegister() whether it's running or not
> running on the stack of SmiManage(), and to postpone SMI_HANDLER
> deletion until after the loop finishes in the former case.
> 
> I'm not sure if real life SmiHandlerUnRegister() usage is worth this
> complication, however.
> 
> (2) Independently: does the same issue exist for the StMM core? I seem
> to be discovering the same problem in MmiManage()
> [StandaloneMmPkg/Core/Mmi.c].
> 
> So, whatever patch we add to the SMM_CORE, should likely be reflected to
> MM_CORE_STANDALONE too. Adding Ard and Sami to the CC list.
> 
> Thanks
> Laszlo



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On 1/25/24 13:05, Ni, Ray wrote:
> Laszlo,
> SMI handler is called from SmmCore.
> So SmmCore knows which handle is passed to the SMI handler.
> How about let Unregister() rejects the request coming from a SMI handler which unregisters other handles?
> 
> A "gCurrentSmiHandle" can be assigned before calling the SMI handler and set to NULL when it returns.
> Unregister() compares the handle against gCurrentSmiHandle if it's not NULL.

Sounds safe enough. I don't know if it conforms to the spec however
(although we might just choose not to care about that).

Laszlo



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> Sounds safe enough. I don't know if it conforms to the spec however
> (although we might just choose not to care about that).

Should be compliant to spec. Or I should say spec does not under which case the Unregister() should succeed. As long as spec allows Unregister() returns a failure status,
a very low-quality MmCore could always return failure from Unregister().

Our choice here is to return failure for a special case only (Unregister handler B in handler A).

> 
> Laszlo



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Felix, I remember you mentioned to me about the usage of SMI handler unregistering itself.

Reviewed-by: Ray Ni <ray.ni@intel.com>

Thanks,
Ray
> -----Original Message-----
> From: Liu, Zhiguang <zhiguang.liu@intel.com>
> Sent: Wednesday, January 24, 2024 12:03 PM
> To: devel@edk2.groups.io
> Cc: Liu, Zhiguang <zhiguang.liu@intel.com>; Liming Gao
> <gaoliming@byosoft.com.cn>; Wu, Jiaxin <jiaxin.wu@intel.com>; Ni, Ray
> <ray.ni@intel.com>
> Subject: [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler
> inside SMI handler
> 
> To support unregister SMI handler inside SMI handler itself,
> get next node before SMI handler is executed, since LIST_ENTRY that
> Link points to may be freed if unregister SMI handler in SMI handler
> itself.
> 
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Jiaxin Wu <jiaxin.wu@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
> ---
>  MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c
> b/MdeModulePkg/Core/PiSmmCore/Smi.c
> index 2985f989c3..a75e52b1ae 100644
> --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
> +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
> @@ -134,8 +134,14 @@ SmiManage (
> 
>    Head = &SmiEntry->SmiHandlers;
> 
> -  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
> +  for (Link = Head->ForwardLink; Link != Head;) {
>      SmiHandler = CR (Link, SMI_HANDLER, Link,
> SMI_HANDLER_SIGNATURE);
> +    //
> +    // To support unregiser SMI handler inside SMI handler itself,
> +    // get next node before handler is executed, since LIST_ENTRY that
> +    // Link points to may be freed if unregister SMI handler.
> +    //
> +    Link = Link->ForwardLink;
> 
>      Status = SmiHandler->Handler (
>                             (EFI_HANDLE)SmiHandler,
> --
> 2.31.1.windows.1



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On 1/24/24 09:11, Ni, Ray wrote:
> Felix, I remember you mentioned to me about the usage of SMI handler unregistering itself.

I wanted to ask: is this something that the PI spec comments on? I.e.,
is this usage expected by the spec (in which case this bugfix is a
conformance fix), or is the spec silent on it (in which case I guess we
can call this a quality-of-implementation improvement)?

> 
> Reviewed-by: Ray Ni <ray.ni@intel.com>

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo

> 
> Thanks,
> Ray
>> -----Original Message-----
>> From: Liu, Zhiguang <zhiguang.liu@intel.com>
>> Sent: Wednesday, January 24, 2024 12:03 PM
>> To: devel@edk2.groups.io
>> Cc: Liu, Zhiguang <zhiguang.liu@intel.com>; Liming Gao
>> <gaoliming@byosoft.com.cn>; Wu, Jiaxin <jiaxin.wu@intel.com>; Ni, Ray
>> <ray.ni@intel.com>
>> Subject: [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler
>> inside SMI handler
>>
>> To support unregister SMI handler inside SMI handler itself,
>> get next node before SMI handler is executed, since LIST_ENTRY that
>> Link points to may be freed if unregister SMI handler in SMI handler
>> itself.
>>
>> Cc: Liming Gao <gaoliming@byosoft.com.cn>
>> Cc: Jiaxin Wu <jiaxin.wu@intel.com>
>> Cc: Ray Ni <ray.ni@intel.com>
>> Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
>> ---
>>  MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c
>> b/MdeModulePkg/Core/PiSmmCore/Smi.c
>> index 2985f989c3..a75e52b1ae 100644
>> --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
>> +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
>> @@ -134,8 +134,14 @@ SmiManage (
>>
>>    Head = &SmiEntry->SmiHandlers;
>>
>> -  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
>> +  for (Link = Head->ForwardLink; Link != Head;) {
>>      SmiHandler = CR (Link, SMI_HANDLER, Link,
>> SMI_HANDLER_SIGNATURE);
>> +    //
>> +    // To support unregiser SMI handler inside SMI handler itself,
>> +    // get next node before handler is executed, since LIST_ENTRY that
>> +    // Link points to may be freed if unregister SMI handler.
>> +    //
>> +    Link = Link->ForwardLink;
>>
>>      Status = SmiHandler->Handler (
>>                             (EFI_HANDLE)SmiHandler,
>> --
>> 2.31.1.windows.1
> 
> 
> 
> 
> 
> 



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spec does not say the unregistration is allowed inside handler. it's just to improve the qualiquali the code.

thanks,
ray
________________________________
From: Laszlo Ersek <lersek@redhat.com>
Sent: Wednesday, January 24, 2024 9:06:13 PM
To: devel@edk2.groups.io <devel@edk2.groups.io>; Ni, Ray <ray.ni@intel.com>; Liu, Zhiguang <zhiguang.liu@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>; Wu, Jiaxin <jiaxin.wu@intel.com>; POLUDOV, FELIX <felixp@ami.com>
Subject: Re: [edk2-devel] [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler inside SMI handler

On 1/24/24 09:11, Ni, Ray wrote:
> Felix, I remember you mentioned to me about the usage of SMI handler unregistering itself.

I wanted to ask: is this something that the PI spec comments on? I.e.,
is this usage expected by the spec (in which case this bugfix is a
conformance fix), or is the spec silent on it (in which case I guess we
can call this a quality-of-implementation improvement)?

>
> Reviewed-by: Ray Ni <ray.ni@intel.com>

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo

>
> Thanks,
> Ray
>> -----Original Message-----
>> From: Liu, Zhiguang <zhiguang.liu@intel.com>
>> Sent: Wednesday, January 24, 2024 12:03 PM
>> To: devel@edk2.groups.io
>> Cc: Liu, Zhiguang <zhiguang.liu@intel.com>; Liming Gao
>> <gaoliming@byosoft.com.cn>; Wu, Jiaxin <jiaxin.wu@intel.com>; Ni, Ray
>> <ray.ni@intel.com>
>> Subject: [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler
>> inside SMI handler
>>
>> To support unregister SMI handler inside SMI handler itself,
>> get next node before SMI handler is executed, since LIST_ENTRY that
>> Link points to may be freed if unregister SMI handler in SMI handler
>> itself.
>>
>> Cc: Liming Gao <gaoliming@byosoft.com.cn>
>> Cc: Jiaxin Wu <jiaxin.wu@intel.com>
>> Cc: Ray Ni <ray.ni@intel.com>
>> Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
>> ---
>>  MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c
>> b/MdeModulePkg/Core/PiSmmCore/Smi.c
>> index 2985f989c3..a75e52b1ae 100644
>> --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
>> +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
>> @@ -134,8 +134,14 @@ SmiManage (
>>
>>    Head = &SmiEntry->SmiHandlers;
>>
>> -  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
>> +  for (Link = Head->ForwardLink; Link != Head;) {
>>      SmiHandler = CR (Link, SMI_HANDLER, Link,
>> SMI_HANDLER_SIGNATURE);
>> +    //
>> +    // To support unregiser SMI handler inside SMI handler itself,
>> +    // get next node before handler is executed, since LIST_ENTRY that
>> +    // Link points to may be freed if unregister SMI handler.
>> +    //
>> +    Link = Link->ForwardLink;
>>
>>      Status = SmiHandler->Handler (
>>                             (EFI_HANDLE)SmiHandler,
>> --
>> 2.31.1.windows.1
>
>
>
> 
>
>



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In my opinion this is not a spec conformance fix, but it is a bug fix.
The spec does not explicitly mentions unregistering from within the handler,
but by applying a principle that everything that's not forbidden is legal,
it's fair for a caller to expect that unregistering works fine in any valid context
including from within the MM handler.

The spec does mention that UEFI/PI interfaces are not reentrant,
however, reentrancy typically implies repetitive invocation of the same interface,
not a call to one MM Core interface while another MM Core interface is in progress.

From: Ni, Ray <ray.ni@intel.com>
Sent: Wednesday, January 24, 2024 11:17 AM
To: Laszlo Ersek <lersek@redhat.com>; devel@edk2.groups.io; Liu, Zhiguang <zhiguang.liu@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>; Wu, Jiaxin <jiaxin.wu@intel.com>; Felix Polyudov <Felixp@ami.com>
Subject: [EXTERNAL] Re: [edk2-devel] [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler inside SMI handler


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spec does not say the unregistration is allowed inside handler. it's just to improve the qualiquali the code.

thanks,
ray
________________________________
From: Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>>
Sent: Wednesday, January 24, 2024 9:06:13 PM
To: devel@edk2.groups.io<mailto:devel@edk2.groups.io> <devel@edk2.groups.io<mailto:devel@edk2.groups.io>>; Ni, Ray <ray.ni@intel.com<mailto:ray.ni@intel.com>>; Liu, Zhiguang <zhiguang.liu@intel.com<mailto:zhiguang.liu@intel.com>>
Cc: Liming Gao <gaoliming@byosoft.com.cn<mailto:gaoliming@byosoft.com.cn>>; Wu, Jiaxin <jiaxin.wu@intel.com<mailto:jiaxin.wu@intel.com>>; POLUDOV, FELIX <felixp@ami.com<mailto:felixp@ami.com>>
Subject: Re: [edk2-devel] [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler inside SMI handler

On 1/24/24 09:11, Ni, Ray wrote:
> Felix, I remember you mentioned to me about the usage of SMI handler unregistering itself.

I wanted to ask: is this something that the PI spec comments on? I.e.,
is this usage expected by the spec (in which case this bugfix is a
conformance fix), or is the spec silent on it (in which case I guess we
can call this a quality-of-implementation improvement)?

>
> Reviewed-by: Ray Ni <ray.ni@intel.com<mailto:ray.ni@intel.com>>

Reviewed-by: Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>>

Thanks
Laszlo

>
> Thanks,
> Ray
>> -----Original Message-----
>> From: Liu, Zhiguang <zhiguang.liu@intel.com<mailto:zhiguang.liu@intel.com>>
>> Sent: Wednesday, January 24, 2024 12:03 PM
>> To: devel@edk2.groups.io<mailto:devel@edk2.groups.io>
>> Cc: Liu, Zhiguang <zhiguang.liu@intel.com<mailto:zhiguang.liu@intel.com>>; Liming Gao
>> <gaoliming@byosoft.com.cn<mailto:gaoliming@byosoft.com.cn>>; Wu, Jiaxin <jiaxin.wu@intel.com<mailto:jiaxin.wu@intel.com>>; Ni, Ray
>> <ray.ni@intel.com<mailto:ray.ni@intel.com>>
>> Subject: [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler
>> inside SMI handler
>>
>> To support unregister SMI handler inside SMI handler itself,
>> get next node before SMI handler is executed, since LIST_ENTRY that
>> Link points to may be freed if unregister SMI handler in SMI handler
>> itself.
>>
>> Cc: Liming Gao <gaoliming@byosoft.com.cn<mailto:gaoliming@byosoft.com.cn>>
>> Cc: Jiaxin Wu <jiaxin.wu@intel.com<mailto:jiaxin.wu@intel.com>>
>> Cc: Ray Ni <ray.ni@intel.com<mailto:ray.ni@intel.com>>
>> Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com<mailto:zhiguang.liu@intel.com>>
>> ---
>>  MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c
>> b/MdeModulePkg/Core/PiSmmCore/Smi.c
>> index 2985f989c3..a75e52b1ae 100644
>> --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
>> +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
>> @@ -134,8 +134,14 @@ SmiManage (
>>
>>    Head = &SmiEntry->SmiHandlers;
>>
>> -  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
>> +  for (Link = Head->ForwardLink; Link != Head;) {
>>      SmiHandler = CR (Link, SMI_HANDLER, Link,
>> SMI_HANDLER_SIGNATURE);
>> +    //
>> +    // To support unregiser SMI handler inside SMI handler itself,
>> +    // get next node before handler is executed, since LIST_ENTRY that
>> +    // Link points to may be freed if unregister SMI handler.
>> +    //
>> +    Link = Link->ForwardLink;
>>
>>      Status = SmiHandler->Handler (
>>                             (EFI_HANDLE)SmiHandler,
>> --
>> 2.31.1.windows.1
>
>
>
> 
>
>
-The information contained in this message may be confidential and proprietary to American Megatrends (AMI). This communication is intended to be read only by the individual or entity to whom it is addressed or by their designee. If the reader of this message is not the intended recipient, you are on notice that any distribution of this message, in any form, is strictly prohibited. Please promptly notify the sender by reply e-mail or by telephone at 770-246-8600, and then delete or destroy all copies of the transmission.


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On 1/24/24 18:15, Felix Polyudov via groups.io wrote:
> In my opinion this is not a spec conformance fix, but it is a bug fix.
> 
> The spec does not explicitly mentions unregistering from within the handler,
> 
> but by applying a principle that everything that’s not forbidden is legal,
> 
> it’s fair for a caller to expect that unregistering works fine in any
> valid context
> 
> including from within the MM handler.
> 
>  
> 
> The spec does mention that UEFI/PI interfaces are not reentrant,
> 
> however, reentrancy typically implies repetitive invocation of the same
> interface,
> 
> not a call to one MM Core interface while another MM Core interface is
> in progress.

Sure, I'm not contesting any of that; it's great that you and Ray seem
to agree. I just wanted to understand. My R-b stands.

Thanks!
Laszlo

> *From:*Ni, Ray <ray.ni@intel.com>
> *Sent:* Wednesday, January 24, 2024 11:17 AM
> *To:* Laszlo Ersek <lersek@redhat.com>; devel@edk2.groups.io; Liu,
> Zhiguang <zhiguang.liu@intel.com>
> *Cc:* Liming Gao <gaoliming@byosoft.com.cn>; Wu, Jiaxin
> <jiaxin.wu@intel.com>; Felix Polyudov <Felixp@ami.com>
> *Subject:* [EXTERNAL] Re: [edk2-devel] [PATCH] MdeModulePkg/SMM: Support
> to unregister SMI handler inside SMI handler
> 
>  
> 
>  
> 
> ***CAUTION:*The e-mail below is from an external source. Please exercise
> caution before opening attachments, clicking links, or following
> guidance.**
> 
> spec does not say the unregistration is allowed inside handler. it's
> just to improve the qualiquali the code.
> 
>  
> 
> thanks,
> 
> ray
> 
> ------------------------------------------------------------------------
> 
> *From:*Laszlo Ersek <lersek@redhat.com <mailto:lersek@redhat.com>>
> *Sent:* Wednesday, January 24, 2024 9:06:13 PM
> *To:* devel@edk2.groups.io <mailto:devel@edk2.groups.io>
> <devel@edk2.groups.io <mailto:devel@edk2.groups.io>>; Ni, Ray
> <ray.ni@intel.com <mailto:ray.ni@intel.com>>; Liu, Zhiguang
> <zhiguang.liu@intel.com <mailto:zhiguang.liu@intel.com>>
> *Cc:* Liming Gao <gaoliming@byosoft.com.cn
> <mailto:gaoliming@byosoft.com.cn>>; Wu, Jiaxin <jiaxin.wu@intel.com
> <mailto:jiaxin.wu@intel.com>>; POLUDOV, FELIX <felixp@ami.com
> <mailto:felixp@ami.com>>
> *Subject:* Re: [edk2-devel] [PATCH] MdeModulePkg/SMM: Support to
> unregister SMI handler inside SMI handler
> 
>  
> 
> On 1/24/24 09:11, Ni, Ray wrote:
>> Felix, I remember you mentioned to me about the usage of SMI handler unregistering itself.
> 
> I wanted to ask: is this something that the PI spec comments on? I.e.,
> is this usage expected by the spec (in which case this bugfix is a
> conformance fix), or is the spec silent on it (in which case I guess we
> can call this a quality-of-implementation improvement)?
> 
>> 
>> Reviewed-by: Ray Ni <ray.ni@intel.com <mailto:ray.ni@intel.com>>
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com <mailto:lersek@redhat.com>>
> 
> Thanks
> Laszlo
> 
>> 
>> Thanks,
>> Ray
>>> -----Original Message-----
>>> From: Liu, Zhiguang <zhiguang.liu@intel.com <mailto:zhiguang.liu@intel.com>>
>>> Sent: Wednesday, January 24, 2024 12:03 PM
>>> To: devel@edk2.groups.io <mailto:devel@edk2.groups.io>
>>> Cc: Liu, Zhiguang <zhiguang.liu@intel.com <mailto:zhiguang.liu@intel.com>>; Liming Gao
>>> <gaoliming@byosoft.com.cn <mailto:gaoliming@byosoft.com.cn>>; Wu, Jiaxin
> <jiaxin.wu@intel.com <mailto:jiaxin.wu@intel.com>>; Ni, Ray
>>> <ray.ni@intel.com <mailto:ray.ni@intel.com>>
>>> Subject: [PATCH] MdeModulePkg/SMM: Support to unregister SMI handler
>>> inside SMI handler
>>>
>>> To support unregister SMI handler inside SMI handler itself,
>>> get next node before SMI handler is executed, since LIST_ENTRY that
>>> Link points to may be freed if unregister SMI handler in SMI handler
>>> itself.
>>>
>>> Cc: Liming Gao <gaoliming@byosoft.com.cn <mailto:gaoliming@byosoft.com.cn>>
>>> Cc: Jiaxin Wu <jiaxin.wu@intel.com <mailto:jiaxin.wu@intel.com>>
>>> Cc: Ray Ni <ray.ni@intel.com <mailto:ray.ni@intel.com>>
>>> Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com <mailto:zhiguang.liu@intel.com>>
>>> ---
>>>  MdeModulePkg/Core/PiSmmCore/Smi.c | 8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c
>>> b/MdeModulePkg/Core/PiSmmCore/Smi.c
>>> index 2985f989c3..a75e52b1ae 100644
>>> --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
>>> +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
>>> @@ -134,8 +134,14 @@ SmiManage (
>>>
>>>    Head = &SmiEntry->SmiHandlers;
>>>
>>> -  for (Link = Head->ForwardLink; Link != Head; Link = Link->ForwardLink) {
>>> +  for (Link = Head->ForwardLink; Link != Head;) {
>>>      SmiHandler = CR (Link, SMI_HANDLER, Link,
>>> SMI_HANDLER_SIGNATURE);
>>> +    //
>>> +    // To support unregiser SMI handler inside SMI handler itself,
>>> +    // get next node before handler is executed, since LIST_ENTRY that
>>> +    // Link points to may be freed if unregister SMI handler.
>>> +    //
>>> +    Link = Link->ForwardLink;
>>>
>>>      Status = SmiHandler->Handler (
>>>                             (EFI_HANDLE)SmiHandler,
>>> --
>>> 2.31.1.windows.1
>> 
>> 
>> 
>> 
>> 
>> 
> 
> -The information contained in this message may be confidential and
> proprietary to American Megatrends (AMI). This communication is intended
> to be read only by the individual or entity to whom it is addressed or
> by their designee. If the reader of this message is not the intended
> recipient, you are on notice that any distribution of this message, in
> any form, is strictly prohibited. Please promptly notify the sender by
> reply e-mail or by telephone at 770-246-8600, and then delete or destroy
> all copies of the transmission.
> 



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