[edk2-devel] [PATCH 3/3] UefiCpuPkg/PiSmmCpu: Allow SMM access-out when static paging is OFF

[Laszlo Ersek]

On 07/27/19 05:28, Ni, Ray wrote:
> Commit c60d36b4d1ee1f69b7cca897d3621dfa951895c2
> * UefiCpuPkg/SmmCpu: Block access-out only when static paging is used
> 
> updated page fault handler to treat SMM access-out as allowed
> address when static paging is not used.
> 
> But that commit is not complete because the page table is still
> updated in SetUefiMemMapAttributes() for non-SMRAM memory. When SMM
> code accesses non-SMRAM memory, page fault is still generated.
> 
> This patch skips to update page table for non-SMRAM memory and
> page table itself.
> 
> Signed-off-by: Ray Ni <ray.ni at intel.com>
> Cc: Eric Dong <eric.dong at intel.com>
> Cc: Jiewen Yao <jiewen.yao at intel.com>
> Cc: Jian J Wang <jian.j.wang at intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
> index 69a04dfb23..d7d94c8b6d 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
> @@ -1121,6 +1121,9 @@ FindSmramInfo (
>    *SmrrBase = (UINT32)CurrentSmramRange->CpuStart;
>    *SmrrSize = (UINT32)CurrentSmramRange->PhysicalSize;
>  
> +  //
> +  // Extend *SmrrBase/*SmrrSize to include adjacent SMRAM ranges
> +  //
>    do {
>      Found = FALSE;
>      for (Index = 0; Index < mSmmCpuSmramRangeCount; Index++) {
> @@ -1432,14 +1435,20 @@ PerformRemainingTasks (
>      SetMemMapAttributes ();
>  
>      //
> -    // For outside SMRAM, we only map SMM communication buffer or MMIO.
> +    // Protect memory outside SMRAM when SMM Static Page Table is enabled.
>      //
> -    SetUefiMemMapAttributes ();
> +    if (IsStaticPageTableEnabled ()) {
>  
> -    //
> -    // Set page table itself to be read-only
> -    //
> -    SetPageTableAttributes ();
> +      //
> +      // For outside SMRAM, we only map SMM communication buffer or MMIO.
> +      //
> +      SetUefiMemMapAttributes ();
> +
> +      //
> +      // Set page table itself to be read-only
> +      //
> +      SetPageTableAttributes ();
> +    }
>  
>      //
>      // Configure SMM Code Access Check feature if available.
> 

With the IA32 bug in patch#1 fixed, this patch will also do the right
thing (as part of OVMF anyway):

- on IA32, there will be no change in behavior
(IsStaticPageTableEnabled() will evaluate to constant TRUE)

- on X64, OVMF keeps the DEC-default TRUE value for the underlying PCD
(PcdCpuSmmStaticPageTable), hence IsStaticPageTableEnabled() will return
TRUE, and the behavior won't change.

Because I cannot validate the PcdCpuSmmStaticPageTable==FALSE case, I
won't give R-b. But I can certainly give:

Acked-by: Laszlo Ersek <lersek at redhat.com>

Thanks!
Laszlo

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