[edk2-devel] [Patch V2 1/2] MdeModulePkg/DxeIpl: Remove clearing CR0.WP when protecting pagetable

[Ni, Ray]

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

> -----Original Message-----
> From: Tan, Dun <dun.tan at intel.com>
> Sent: Wednesday, August 10, 2022 1:34 PM
> To: devel at edk2.groups.io
> Cc: Bi, Dandan <dandan.bi at intel.com>; Gao, Liming
> <gaoliming at byosoft.com.cn>; Ni, Ray <ray.ni at intel.com>
> Subject: [Patch V2 1/2] MdeModulePkg/DxeIpl: Remove clearing CR0.WP
> when protecting pagetable
> 
> Remove clearing CR0.WP when marking the memory used for page table
> as read-only in the page table itself created by DxeIpl. This page
> table address is written to Cr3 after these protection steps. Till
> this, the memory used for page table is always RW.
> 
> Signed-off-by: Dun Tan <dun.tan at intel.com>
> Cc: Dandan Bi <dandan.bi at intel.com>
> Cc: Liming Gao <gaoliming at byosoft.com.cn>
> Cc: Ray Ni <ray.ni at intel.com>
> ---
>  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> index a451ca1604..18b121d768 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> @@ -626,12 +626,7 @@ EnablePageTableProtection (
>    }
> 
>    //
> -  // Disable write protection, because we need to mark page table to be
> write
> -  // protected.
> -  //
> -  AsmWriteCr0 (AsmReadCr0 () & ~CR0_WP);
> -
> -  //
> +  // No need to clear CR0.WP since PageTableBase has't been written to CR3
> yet.
>    // SetPageTablePoolReadOnly might update mPageTablePool. It's safer to
>    // remember original one in advance.
>    //
> --
> 2.31.1.windows.1



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