gCpu->SetMemoryAttributes() called by SetUefiImageMemoryAttributes() will return
without any problem if Length is 0.
Regards,
Jian
> -----Original Message-----
> From: Yao, Jiewen
> Sent: Tuesday, January 30, 2018 10:09 AM
> To: Wang, Jian J <jian.j.w...@intel.com>; edk2-devel@lists.01.org
> Cc: Zeng, Star <star.z...@intel.com>; Dong, Eric <eric.d...@intel.com>; Ni,
> Ruiyu <ruiyu...@intel.com>
> Subject: RE: [PATCH] MdeModulePkg/Core: fix feature conflict between NX and
> NULL detection
>
> Hi Jian
> May I know how we handle MemoryMapEntry->NumberOfPages is 1?
> The lengh will be 0 in that case. Should we add additional check?
>
> > + SetUefiImageMemoryAttributes (
> > + MemoryMapEntry->PhysicalStart + EFI_PAGE_SIZE,
> > + LShiftU64 (MemoryMapEntry->NumberOfPages - 1,
> > EFI_PAGE_SHIFT),
> > + Attributes);
>
> > -----Original Message-----
> > From: Wang, Jian J
> > Sent: Monday, January 29, 2018 7:10 PM
> > To: edk2-devel@lists.01.org
> > Cc: Zeng, Star <star.z...@intel.com>; Dong, Eric <eric.d...@intel.com>; Yao,
> > Jiewen <jiewen....@intel.com>; Ni, Ruiyu <ruiyu...@intel.com>
> > Subject: [PATCH] MdeModulePkg/Core: fix feature conflict between NX and
> > NULL detection
> >
> > If enabled, NX memory protection feature will mark all free memory as
> > NX (non-executable), including page 0. This will overwrite the attributes
> > of page 0 if NULL pointer detection feature is also enabled and then
> > compromise the functionality of it. The solution is skipping the NX
> > attributes setting to page 0 if NULL pointer detection feature is enabled.
> >
> > Cc: Star Zeng <star.z...@intel.com>
> > Cc: Eric Dong <eric.d...@intel.com>
> > Cc: Jiewen Yao <jiewen....@intel.com>
> > Cc: Ruiyu Ni <ruiyu...@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Jian J Wang <jian.j.w...@intel.com>
> > ---
> > MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c | 20
> > ++++++++++++++++----
> > 1 file changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
> > b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
> > index 862593f562..150167bf66 100644
> > --- a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
> > +++ b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
> > @@ -845,10 +845,22 @@ InitializeDxeNxMemoryProtectionPolicy (
> >
> > Attributes = GetPermissionAttributeForMemoryType
> > (MemoryMapEntry->Type);
> > if (Attributes != 0) {
> > - SetUefiImageMemoryAttributes (
> > - MemoryMapEntry->PhysicalStart,
> > - LShiftU64 (MemoryMapEntry->NumberOfPages, EFI_PAGE_SHIFT),
> > - Attributes);
> > + if (MemoryMapEntry->PhysicalStart == 0 &&
> > + PcdGet8 (PcdNullPointerDetectionPropertyMask) != 0) {
> > + //
> > + // Skip page 0 if NULL pointer detection is enabled to avoid
> > attributes
> > + // overwritten.
> > + //
> > + SetUefiImageMemoryAttributes (
> > + MemoryMapEntry->PhysicalStart + EFI_PAGE_SIZE,
> > + LShiftU64 (MemoryMapEntry->NumberOfPages - 1,
> > EFI_PAGE_SHIFT),
> > + Attributes);
> > + } else {
> > + SetUefiImageMemoryAttributes (
> > + MemoryMapEntry->PhysicalStart,
> > + LShiftU64 (MemoryMapEntry->NumberOfPages, EFI_PAGE_SHIFT),
> > + Attributes);
> > + }
> > }
> > MemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry,
> > DescriptorSize);
> > }
> > --
> > 2.14.1.windows.1
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