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.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ayellet Wolman <ayellet.wolman@intel.com>
Suggested-by: Ayellet Wolman <ayellet.wolman@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>

Jian J Wang (5):
  MdeModulePkg/DxeIpl: Implement NULL pointer detection
  MdeModulePkg/Core/Dxe: Add EndOfDxe workaround for NULL pointer
    detection
  UefiCpuPkg/PiSmmCpuDxeSmm: Implement NULL pointer detection for SMM
    code
  IntelFrameworkModulePkg/Csm: Add code to bypass NULL pointer detection
  OvmfPkg/QemuVideoDxe: Bypass NULL pointer detection during VBE SHIM
    installing

Wang, Jian J (1):
  MdeModulePkg/MdeModulePkg.dec,.uni: Add NULL pointer detection PCD

 .../Csm/BiosThunk/KeyboardDxe/BiosKeyboard.c       | 101 ++++++++++++++
 .../Csm/BiosThunk/KeyboardDxe/BiosKeyboard.h       |   2 +
 .../Csm/BiosThunk/KeyboardDxe/KeyboardDxe.inf      |   2 +
 .../Csm/LegacyBiosDxe/LegacyBda.c                  |   4 +
 .../Csm/LegacyBiosDxe/LegacyBios.c                 | 152 +++++++++++++++++++++
 .../Csm/LegacyBiosDxe/LegacyBiosDxe.inf            |   2 +
 .../Csm/LegacyBiosDxe/LegacyBiosInterface.h        |  18 +++
 .../Csm/LegacyBiosDxe/LegacyBootSupport.c          |  23 +++-
 .../Csm/LegacyBiosDxe/LegacyPci.c                  |  17 ++-
 IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Thunk.c  |  27 +++-
 MdeModulePkg/Core/Dxe/DxeMain.inf                  |   1 +
 MdeModulePkg/Core/Dxe/Mem/Page.c                   |   4 +-
 MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c      |  48 +++++++
 MdeModulePkg/Core/DxeIplPeim/DxeIpl.h              |  25 ++++
 MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf            |   1 +
 MdeModulePkg/Core/DxeIplPeim/DxeLoad.c             |  65 +++++++++
 MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c    |  11 +-
 MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c     |   2 +
 MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c   |  31 ++++-
 MdeModulePkg/MdeModulePkg.dec                      |  13 ++
 MdeModulePkg/MdeModulePkg.uni                      |  13 ++
 OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf              |   1 +
 OvmfPkg/QemuVideoDxe/VbeShim.c                     |  14 ++
 UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c           |  12 ++
 UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c              |  25 +++-
 UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.inf       |   1 +
 UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c            |  12 ++
 27 files changed, 606 insertions(+), 21 deletions(-)

-- 
2.14.1.windows.1

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