Re: [edk2-devel] [PATCH 3/5] UefiCpuPkg/PiSmmCpu: Restrict access per PcdCpuSmmRestrictedMemoryAccess

["Laszlo Ersek" <lersek@redhat.com>]

On 08/26/19 00:45, Ni, Ray wrote:
> Today's behavior is to always restrict access to non-SMRAM regardless
> the value of PcdCpuSmmRestrictedMemoryAccess.
> 
> Because RAS components require to access all non-SMRAM memory, the
> patch changes the code logic to honor PcdCpuSmmRestrictedMemoryAccess
> so that only when the PCD is true, the restriction takes affect and
> page table memory is also protected.
> 
> Because IA32 build doesn't reference this PCD, such restriction
> always takes affect in IA32 build.
> 
> Signed-off-by: Ray Ni <ray.ni@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c   | 14 ++++++++++++++
>  UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c | 18 ++++++++++--------
>  UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h | 11 +++++++++++
>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c    | 14 ++++++++++++++
>  4 files changed, 49 insertions(+), 8 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c
> index 05fb455936..f891a81112 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c
> @@ -336,3 +336,17 @@ RestoreCr2 (
>  {
>    return ;
>  }
> +
> +/**
> +  Return whether access to non-SMRAM is restricted.
> +
> +  @retval TRUE  Access to non-SMRAM is restricted.
> +  @retval FALSE Access to non-SMRAM is not restricted.
> +*/
> +BOOLEAN
> +IsRestrictedMemoryAccess (
> +  VOID
> +  )
> +{
> +  return TRUE;
> +}
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
> index 69a04dfb23..723fd5042f 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
> @@ -1431,15 +1431,17 @@ PerformRemainingTasks (
>      //
>      SetMemMapAttributes ();
>  
> -    //
> -    // For outside SMRAM, we only map SMM communication buffer or MMIO.
> -    //
> -    SetUefiMemMapAttributes ();
> +    if (IsRestrictedMemoryAccess ()) {
> +      //
> +      // For outside SMRAM, we only map SMM communication buffer or MMIO.
> +      //
> +      SetUefiMemMapAttributes ();
>  
> -    //
> -    // Set page table itself to be read-only
> -    //
> -    SetPageTableAttributes ();
> +      //
> +      // Set page table itself to be read-only
> +      //
> +      SetPageTableAttributes ();
> +    }
>  
>      //
>      // Configure SMM Code Access Check feature if available.
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
> index 8c29f1a558..daf977f654 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
> @@ -1450,4 +1450,15 @@ InitializeDataForMmMp (
>    VOID
>    );
>  
> +/**
> +  Return whether access to non-SMRAM is restricted.
> +
> +  @retval TRUE  Access to non-SMRAM is restricted.
> +  @retval FALSE Access to non-SMRAM is not restricted.
> +*/
> +BOOLEAN
> +IsRestrictedMemoryAccess (
> +  VOID
> +  );
> +
>  #endif
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> index 7516f35055..733d107efd 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> @@ -1252,3 +1252,17 @@ RestoreCr2 (
>      AsmWriteCr2 (Cr2);
>    }
>  }
> +
> +/**
> +  Return whether access to non-SMRAM is restricted.
> +
> +  @retval TRUE  Access to non-SMRAM is restricted.
> +  @retval FALSE Access to non-SMRAM is not restricted.
> +*/
> +BOOLEAN
> +IsRestrictedMemoryAccess (
> +  VOID
> +  )
> +{
> +  return mCpuSmmRestrictedMemoryAccess;
> +}
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>