[edk2-devel] [PATCH 0/2] Fix #DF issue when enable CET shadow stack feature.

[Sheng Wei]

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.
The busy bit should be cleared when return back form SMM exception to SMM
handler. Otherwise, keeping busy bit in set state 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.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3192

Signed-off-by: Sheng Wei <w.sheng at intel.com>
Cc: Michael D Kinney <michael.d.kinney at intel.com>
Cc: Liming Gao <gaoliming at byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu at intel.com>
Cc: Jiewen Yao <jiewen.yao at intel.com>
Cc: Eric Dong <eric.dong at intel.com>
Cc: Ray Ni <ray.ni at intel.com>
Cc: Laszlo Ersek <lersek at redhat.com>
Cc: Rahul Kumar <rahul1.kumar at 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                       | 14 ++++++++++-
 MdePkg/Include/X64/Nasm.inc                        | 14 ++++++++++-
 .../DxeCpuExceptionHandlerLib.inf                  |  3 +++
 .../PeiCpuExceptionHandlerLib.inf                  |  3 +++
 .../SecPeiCpuExceptionHandlerLib.inf               |  4 ++++
 .../SmmCpuExceptionHandlerLib.inf                  |  3 +++
 .../X64/Xcode5ExceptionHandlerAsm.nasm             | 28 +++++++++++++++++++++-
 .../Xcode5SecPeiCpuExceptionHandlerLib.inf         |  4 ++++
 8 files changed, 70 insertions(+), 3 deletions(-)

-- 
2.16.2.windows.1



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