The mechanism behind is to trigger a page fault exception at address 0. This can be made by disabling page 0 (0-4095) during page table setup. So this feature can only be available on platform with paging enabled. Once this feature is enabled, any code, like CSM, which has to access memory in page 0 needs to enable this page temporarily in advance and disable it afterwards. PcdNullPointerDetectionPropertyMask is used to control and elaborate the use cases. For example, BIT7 of this PCD must be set for Windows 7 boot on Qemu if BIT0 set; or boot will fail.

Wang, Jian J (4):
  Implement NULL pointer detection in EDK-II Core.
  Implement NULL pointer detection for SMM mode code.
  Update CSM code to temporarily bypass NULL pointer detection if
    enabled.
  Update QemuVideoDxe driver to bypass NULL pointer detection if
    enabled.

 .../Csm/BiosThunk/KeyboardDxe/BiosKeyboard.c       | 10 +++-
 .../Csm/BiosThunk/KeyboardDxe/BiosKeyboard.h       | 18 +++++++
 .../Csm/BiosThunk/KeyboardDxe/KeyboardDxe.inf      |  2 +
 .../Csm/LegacyBiosDxe/LegacyBda.c                  |  4 ++
 .../Csm/LegacyBiosDxe/LegacyBios.c                 | 55 ++++++++++++++++++----
 .../Csm/LegacyBiosDxe/LegacyBiosDxe.inf            |  2 +
 .../Csm/LegacyBiosDxe/LegacyBiosInterface.h        | 23 +++++++++
 .../Csm/LegacyBiosDxe/LegacyBootSupport.c          | 33 ++++++++++---
 .../Csm/LegacyBiosDxe/LegacyPci.c                  | 17 ++++++-
 IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Thunk.c  | 41 ++++++++++------
 MdeModulePkg/Core/Dxe/DxeMain.inf                  |  3 +-
 MdeModulePkg/Core/Dxe/Mem/Page.c                   | 21 +++++----
 MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c      | 47 ++++++++++++++++++
 MdeModulePkg/Core/DxeIplPeim/DxeIpl.h              | 15 ++++++
 MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf            |  3 +-
 MdeModulePkg/Core/DxeIplPeim/DxeLoad.c             | 53 +++++++++++++++++++++
 MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c    |  8 +++-
 MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c     |  2 +
 MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c   | 23 ++++++---
 MdeModulePkg/MdeModulePkg.dec                      | 12 +++++
 OvmfPkg/QemuVideoDxe/Driver.c                      | 15 +++++-
 OvmfPkg/QemuVideoDxe/Qemu.h                        | 16 +++++++
 OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf              |  2 +
 UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c           | 11 +++++
 UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c              | 25 +++++++++-
 UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h         |  2 +
 UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.inf       | 17 +++----
 UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c            | 11 +++++
 28 files changed, 429 insertions(+), 62 deletions(-)

-- 
2.14.1.windows.1

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