Re: [PATCH] MdeModulePkg/Core: fix feature conflict between NX and NULL detection

["Yao, Jiewen" <jiewen.yao@intel.com>]

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.zeng@intel.com>; Dong, Eric <eric.dong@intel.com>; Yao,
> Jiewen <jiewen.yao@intel.com>; Ni, Ruiyu <ruiyu.ni@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.zeng@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@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