Re: [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm:Fix PF issue caused by smm page table code

["duntan" <dun.tan@intel.com>]

Ray,
Thanks for the comments. Will send V2 patch soon.

Thanks,
Dun

-----Original Message-----
From: Ni, Ray <ray.ni@intel.com> 
Sent: Tuesday, January 3, 2023 11:23 AM
To: Tan, Dun <dun.tan@intel.com>; devel@edk2.groups.io
Cc: Dong, Eric <eric.dong@intel.com>; Kumar, Rahul R <rahul.r.kumar@intel.com>
Subject: RE: [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm:Fix PF issue caused by smm page table code

Dun,
CET should be disabled before clearing CR0.WP.

> -----Original Message-----
> From: Tan, Dun <dun.tan@intel.com>
> Sent: Tuesday, January 3, 2023 10:57 AM
> 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] UefiCpuPkg/PiSmmCpuDxeSmm:Fix PF issue caused by smm 
> page table code
> 
> When setting new page table pool to RO, only disable/enable WP when 
> Cr0.WP has been set to 1 to fix potential PF caused by b822be1a20
> (UefiCpuPkg/PiSmmCpuDxeSmm: Introduce page table pool mechanism).
> With previous code, if someone want to modify the page table and 
> Cr0.WP has been cleared before modify page table, Cr0.WP may be set to 
> 1 again since new pool may be generated during this process Then PF 
> fault may happens.
> 
> 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 | 40 
> ++++++++++++++++++++++++++++------------
>  1 file changed, 28 insertions(+), 12 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> index 4bb23f6920..c385f12d9c 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c
> @@ -67,8 +67,10 @@ InitializePageTablePool (
>    IN UINTN  PoolPages
>    )
>  {
> -  VOID     *Buffer;
> -  BOOLEAN  CetEnabled;
> +  VOID      *Buffer;
> +  BOOLEAN   CetEnabled;
> +  BOOLEAN   WpEnabled;
> +  IA32_CR0  Cr0;
> 
>    //
>    // Always reserve at least PAGE_TABLE_POOL_UNIT_PAGES, including 
> one page for @@ -106,21 +108,35 @@ InitializePageTablePool (
>    //
>    if (mIsReadOnlyPageTable) {
>      CetEnabled = ((AsmReadCr4 () & CR4_CET_ENABLE) != 0) ? TRUE : FALSE;
> -    if (CetEnabled) {
> +    Cr0.UintN  = AsmReadCr0 ();
> +    WpEnabled  = (Cr0.Bits.WP != 0) ? TRUE : FALSE;
> +    if (WpEnabled) {
>        //
> -      // CET must be disabled if WP is disabled.
> +      // Only disable/enable WP when Cr0.Bits.WP has been set to 1.
>        //
> -      DisableCet ();
> +      Cr0.Bits.WP = 0;
> +      AsmWriteCr0 (Cr0.UintN);
> +
> +      if (CetEnabled) {
> +        //
> +        // CET must be disabled if WP is disabled.
> +        //
> +        DisableCet ();
> +      }
>      }
> 
> -    AsmWriteCr0 (AsmReadCr0 () & ~CR0_WP);
>      SmmSetMemoryAttributes ((EFI_PHYSICAL_ADDRESS)(UINTN)Buffer, 
> EFI_PAGES_TO_SIZE (PoolPages), EFI_MEMORY_RO);
> -    AsmWriteCr0 (AsmReadCr0 () | CR0_WP);
> -    if (CetEnabled) {
> -      //
> -      // re-enable CET.
> -      //
> -      EnableCet ();
> +    if (WpEnabled) {
> +      Cr0.UintN   = AsmReadCr0 ();
> +      Cr0.Bits.WP = 1;
> +      AsmWriteCr0 (Cr0.UintN);
> +
> +      if (CetEnabled) {
> +        //
> +        // re-enable CET.
> +        //
> +        EnableCet ();
> +      }
>      }
>    }
> 
> --
> 2.31.1.windows.1