Re: [edk2-devel] [PATCH v8 35/46] OvmfPkg/PlatformPei: Reserve SEV-ES work area if S3 is supported

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

On 05/19/20 23:51, Lendacky, Thomas wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
> 
> Protect the SEV-ES work area memory used by an SEV-ES guest.
> 
> Regarding the lifecycle of the SEV-ES memory area:
>   PcdSevEsWorkArea
> 
> (a) when and how it is initialized after first boot of the VM
> 
>   If SEV-ES is enabled, the SEV-ES area is initialized during
>   the SEC phase [OvmfPkg/ResetVector/Ia32/PageTables64.asm].
> 
> (b) how it is protected from memory allocations during DXE
> 
>   If SEV-ES is enabled, then InitializeRamRegions()
>   [OvmfPkg/PlatformPei/MemDetect.c] protects the ranges with either
>   an AcpiNVS (S3 enabled) or BootServicesData (S3 disabled) memory
>   allocation HOB, in PEI.
> 
> (c) how it is protected from the OS
> 
>   If S3 is enabled, then (b) reserves it from the OS too.
> 
>   If S3 is disabled, then the range needs no protection.
> 
> (d) how it is accessed on the S3 resume path
> 
>   It is rewritten same as in (a), which is fine because (b) reserved it.
> 
> (e) how it is accessed on the warm reset path
> 
>   It is rewritten same as in (a).
> 
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Anthony Perard <anthony.perard@citrix.com>
> Cc: Julien Grall <julien@xen.org>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  OvmfPkg/PlatformPei/PlatformPei.inf |  2 ++
>  OvmfPkg/PlatformPei/MemDetect.c     | 20 ++++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
> index 4742e1bdf42b..c53be2f4925c 100644
> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
> @@ -118,6 +118,8 @@ [FixedPcd]
>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiRuntimeServicesCode
>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiRuntimeServicesData
> +  gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
> +  gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaSize
>  
>  [FeaturePcd]
>    gUefiOvmfPkgTokenSpaceGuid.PcdCsmEnable
> diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
> index 6b5fee166b5d..ffbbef891a11 100644
> --- a/OvmfPkg/PlatformPei/MemDetect.c
> +++ b/OvmfPkg/PlatformPei/MemDetect.c
> @@ -940,5 +940,25 @@ InitializeRamRegions (
>            );
>        }
>      }
> +
> +#ifdef MDE_CPU_X64
> +    if (MemEncryptSevEsIsEnabled ()) {
> +      //
> +      // If SEV-ES is enabled, reserve the SEV-ES work area.
> +      //
> +      // Since this memory range will be used by the Reset Vector on S3
> +      // resume, it must be reserved as ACPI NVS.
> +      //
> +      // If S3 is unsupported, then various drivers might still write to the
> +      // work area. We ought to prevent DXE from serving allocation requests
> +      // such that they would overlap the work area.
> +      //
> +      BuildMemoryAllocationHob (
> +        (EFI_PHYSICAL_ADDRESS)(UINTN) FixedPcdGet32 (PcdSevEsWorkAreaBase),
> +        (UINT64)(UINTN) FixedPcdGet32 (PcdSevEsWorkAreaSize),
> +        mS3Supported ? EfiACPIMemoryNVS : EfiBootServicesData
> +        );
> +    }
> +#endif
>    }
>  }
> 

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