Re: [Patch V2 1/2] UefiCpuPkg/PiSmmCpuDxeSmm: Add a new mIsShadowStack flag

["Ni, Ray" <ray.ni@intel.com>]

Reviewed-by: Ray Ni <ray.ni@intel.com>

> -----Original Message-----
> From: Tan, Dun <dun.tan@intel.com>
> Sent: Wednesday, August 10, 2022 1:37 PM
> To: devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Kumar,
> Rahul R <rahul.r.kumar@intel.com>
> Subject: [Patch V2 1/2] UefiCpuPkg/PiSmmCpuDxeSmm: Add a new
> mIsShadowStack flag
> 
> This patch is code refactoring and doesn't change any functionality.
> Add a new IsShadowStack flag to identify whether current memory is
> shadow stack. Previous smm code logic regards a RO range as shadow
> stack and set the dirty bit in corresponding page table entry if
> mInternalCr3 is not 0, which may be confusing.
> 
> Signed-off-by: Dun Tan <dun.tan@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c | 8
> +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git
> a/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> index 1f7cc15727..237742d7e6 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> @@ -33,6 +33,7 @@ PAGE_ATTRIBUTE_TABLE  mPageAttributeTable[] = {
>  };
> 
>  UINTN  mInternalCr3;
> +UINTN  mIsShadowStack = FALSE;
> 
>  /**
>    Set the internal page table base address.
> @@ -249,7 +250,7 @@ ConvertPageEntryAttribute (
>    if ((Attributes & EFI_MEMORY_RO) != 0) {
>      if (IsSet) {
>        NewPageEntry &= ~(UINT64)IA32_PG_RW;
> -      if (mInternalCr3 != 0) {
> +      if (mIsShadowStack) {
>          // Environment setup
>          // ReadOnly page need set Dirty bit for shadow stack
>          NewPageEntry |= IA32_PG_D;
> @@ -734,10 +735,11 @@ SetShadowStack (
>    EFI_STATUS  Status;
> 
>    SetPageTableBase (Cr3);
> -
> -  Status = SmmSetMemoryAttributes (BaseAddress, Length,
> EFI_MEMORY_RO);
> +  mIsShadowStack = TRUE;
> +  Status         = SmmSetMemoryAttributes (BaseAddress, Length,
> EFI_MEMORY_RO);
> 
>    SetPageTableBase (0);
> +  mIsShadowStack = FALSE;
> 
>    return Status;
>  }
> --
> 2.31.1.windows.1