Hi All,
I update the patch to v4 for refine the comment and commit message.

These patches are used to fix SMM CET shadow stack token busy bit issue.

Issue description:
If CET shadows stack feature enabled in SMM and stack switch is enabled.
When code execute from SMM handler to SMM exception, CPU will check SMM
exception shadow stack token busy bit if it is cleared or not.
If it is set, it will trigger #DF exception.
If it is not set, CPU will set the busy bit when enter SMM exception.
So, the busy bit should be cleared when return back form SMM exception to
SMM handler. Otherwise, keeping busy bit 1 will cause to trigger #DF
exception when enter SMM exception next time.
So, we use instruction SAVEPREVSSP, CLRSSBSY and RSTORSSP to clear the
shadow stack token busy bit before RETF instruction in SMM exception.
Open CI is using NSAM 2.14.02, and it does not support CET instructions.
These instructions are supported since NSAM 2.15.01.
So, I add some CET instructions to nasm.inc.

Could you help to review and give "Review-by" for these patches?

BR
Thank you.
Sheng Wei

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Sheng
> Wei
> Sent: 2021Äê2ÔÂ19ÈÕ 12:48
> To: devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Laszlo
> Ersek <lersek@redhat.com>; Kumar, Rahul1 <rahul1.kumar@intel.com>; Yao,
> Jiewen <jiewen.yao@intel.com>; Kinney, Michael D
> <michael.d.kinney@intel.com>; Liming Gao <gaoliming@byosoft.com.cn>;
> Liu, Zhiguang <zhiguang.liu@intel.com>; Feng, Roger <roger.feng@intel.com>
> Subject: [edk2-devel] [PATCH v4 0/2] Fix CET shadow stack token busy bit
> clear issue
> 
> If CET shadows stack feature enabled in SMM and stack switch is enabled.
> When code execute from SMM handler to SMM exception, CPU will check
> SMM exception shadow stack token busy bit if it is cleared or not.
> If it is set, it will trigger #DF exception.
> If it is not set, CPU will set the busy bit when enter SMM exception.
> So, the busy bit should be cleared when return back form SMM exception to
> SMM handler. Otherwise, keeping busy bit 1 will cause to trigger #DF
> exception when enter SMM exception next time.
> So, we use instruction SAVEPREVSSP, CLRSSBSY and RSTORSSP to clear the
> shadow stack token busy bit before RETF instruction in SMM exception.
> Since open CI is using NASM 2.14.02, it has not supported CET instructions yet.
> Use DB xx xx xx xx to replace the assembly instruction before NASM
> 2.15.01 is used.
> 
> Change from patch v1 to patch v2:
> 1 Add behavior description in source code comment.
> 2 Structure interrupt shadow stack memory in InitShadowStack().
> 3 Update commit comment.
> 
> Change from patch v2 to patch v3:
> 1 Add comment /UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
> 
> Change from patch v3 to patch v4:
> Update comment and commit message.
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3192
> 
> Signed-off-by: Sheng Wei <w.sheng@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Zhiguang Liu <zhiguang.liu@intel.com>
> Cc: Roger Feng <roger.feng@intel.com>
> 
> Sheng Wei (2):
>   MdePkg/Include: Add CET instructions to Nasm.inc
>   UefiCpuPkg/CpuExceptionHandlerLib: Clear CET shadow stack token busy
>     bit
> 
>  MdePkg/Include/Ia32/Nasm.inc                       | 12 ++++++
>  MdePkg/Include/X64/Nasm.inc                        | 12 ++++++
>  .../DxeCpuExceptionHandlerLib.inf                  |  3 ++
>  .../PeiCpuExceptionHandlerLib.inf                  |  3 ++
>  .../SecPeiCpuExceptionHandlerLib.inf               |  4 ++
>  .../SmmCpuExceptionHandlerLib.inf                  |  3 ++
>  .../X64/Xcode5ExceptionHandlerAsm.nasm             | 46
> +++++++++++++++++++++-
>  .../Xcode5SecPeiCpuExceptionHandlerLib.inf         |  4 ++
>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c       | 15 ++++++-
>  9 files changed, 99 insertions(+), 3 deletions(-)
> 
> --
> 2.16.2.windows.1
> 
> 
> 
> 
>