Re: [PATCH v2 2/2] MdeModulePkg/DxeIpl: support more NX related PCDs

["Zeng, Star" <star.zeng@intel.com>]

Jian and Laszlo,

There is also a superficial comment at below.

On 2018/9/20 14:02, Jian J Wang wrote:
>> v2 changes:
>>     a. remove macros no longer needed
>>     b. remove DEBUG and ASSERT in ToEnableExecuteDisableFeature()
>>     c. change ToEnableExecuteDisableFeature to EnableNonExec
> 
> BZ#1116: https://bugzilla.tianocore.org/show_bug.cgi?id=1116
> 
> Currently IA32_EFER.NXE is only set against PcdSetNxForStack. This
> confuses developers because following two other PCDs also need NXE
> to be set, but actually not.
> 
>      PcdDxeNxMemoryProtectionPolicy
>      PcdImageProtectionPolicy
> 
> This patch solves this issue by adding logic to enable IA32_EFER.NXE
> if any of those PCDs have anything enabled.
> 
> Cc: Star Zeng <star.zeng@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> ---
>   MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf          |  2 ++
>   MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |  4 ++--
>   MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 30 +++++++++++++++++++++++-
>   MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h | 24 +++++++++++++++++++
>   4 files changed, 57 insertions(+), 3 deletions(-)
> 
> diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
> index fd82657404..068e700074 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
> +++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
> @@ -117,6 +117,8 @@
>   
>   [Pcd.IA32,Pcd.X64,Pcd.ARM,Pcd.AARCH64]
>     gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack               ## SOMETIMES_CONSUMES
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdDxeNxMemoryProtectionPolicy ## SOMETIMES_CONSUMES
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdImageProtectionPolicy       ## SOMETIMES_CONSUMES
>   
>   [Depex]
>     gEfiPeiLoadFilePpiGuid AND gEfiPeiMasterBootModePpiGuid
> diff --git a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> index d28baa3615..ccd30f964b 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> @@ -245,7 +245,7 @@ ToBuildPageTable (
>       return TRUE;
>     }
>   
> -  if (PcdGetBool (PcdSetNxForStack) && IsExecuteDisableBitAvailable ()) {
> +  if (EnableNonExec ()) {
>       return TRUE;
>     }
>   
> @@ -436,7 +436,7 @@ HandOffToDxeCore (
>       BuildPageTablesIa32Pae = ToBuildPageTable ();
>       if (BuildPageTablesIa32Pae) {
>         PageTables = Create4GPageTablesIa32Pae (BaseOfStack, STACK_SIZE);
> -      if (IsExecuteDisableBitAvailable ()) {
> +      if (EnableNonExec ()) {
>           EnableExecuteDisableBit();
>         }
>       }
> diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> index 496e219913..73b0f67c6b 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> @@ -106,6 +106,31 @@ IsNullDetectionEnabled (
>     return ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT0) != 0);
>   }
>   
> +/**
> +  Check if Execute Disable Bit (IA32_EFER.NXE) should be enabled or not.
> +
> +  @retval TRUE    IA32_EFER.NXE should be enabled.
> +  @retval FALSE   IA32_EFER.NXE should not be enabled.
> +
> +**/
> +BOOLEAN
> +EnableNonExec (
> +  VOID
> +  )
> +{
> +  if (!IsExecuteDisableBitAvailable ()) {
> +    return FALSE;
> +  }
> +
> +  //
> +  // XD flag (BIT63) in page table entry is only valid if IA32_EFER.NXE is set.
> +  // Features controlled by Following PCDs need this feature to be enabled.
> +  //
> +  return (PcdGetBool (PcdSetNxForStack) ||
> +          PcdGet64 (PcdDxeNxMemoryProtectionPolicy) != 0 ||
> +          PcdGet32 (PcdImageProtectionPolicy) != 0);
> +}

I am a little confused by this function name compared with 
EnableExecuteDisableBit(). This function is not really to enable NX, but 
just to check whether enable NX is needed or not. How about using name 
IsEnableNonExecNeeded or IsEnableNxNeeded or IsDisableExecuteNeeded?


Sorry I did not raise this comment in V1 patch thread.
If you agree with the name changing, Reviewed-by: Star Zeng 
<star.zeng@intel.com>.


Thanks,
Star
> +
>   /**
>     Enable Execute Disable Bit.
>   
> @@ -755,7 +780,10 @@ CreateIdentityMappingPageTables (
>     //
>     EnablePageTableProtection ((UINTN)PageMap, TRUE);
>   
> -  if (PcdGetBool (PcdSetNxForStack)) {
> +  //
> +  // Set IA32_EFER.NXE if necessary.
> +  //
> +  if (EnableNonExec ()) {
>       EnableExecuteDisableBit ();
>     }
>   
> diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> index 85457ff937..09085312aa 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> @@ -179,6 +179,30 @@ typedef struct {
>     UINTN           FreePages;
>   } PAGE_TABLE_POOL;
>   
> +/**
> +  Check if Execute Disable Bit (IA32_EFER.NXE) should be enabled or not.
> +
> +  @retval TRUE    IA32_EFER.NXE should be enabled.
> +  @retval FALSE   IA32_EFER.NXE should not be enabled.
> +
> +**/
> +BOOLEAN
> +EnableNonExec (
> +  VOID
> +  );
> +
> +/**
> +  The function will check if Execute Disable Bit is available.
> +
> +  @retval TRUE      Execute Disable Bit is available.
> +  @retval FALSE     Execute Disable Bit is not available.
> +
> +**/
> +BOOLEAN
> +IsExecuteDisableBitAvailable (
> +  VOID
> +  );
> +
>   /**
>     Enable Execute Disable Bit.
>   
>