Re: [edk2-devel] [PATCH v2 05/15] OvmfPkg/MemEncryptSevLib: Save the encryption mask at boot time

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

On 01/06/21 22:21, Lendacky, Thomas wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3108
> 
> The early assembler code performs validation for some of the SEV-related
> information, specifically the encryption bit position. To avoid having to
> re-validate the encryption bit position as the system proceeds through its
> boot phases, save the validated encryption bit position in the SEV-ES work
> area for use by later phases.
> 
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  OvmfPkg/Include/Library/MemEncryptSevLib.h |  2 ++
>  OvmfPkg/ResetVector/Ia32/PageTables64.asm  | 10 +++++++++-
>  OvmfPkg/ResetVector/ResetVector.nasmb      |  1 +
>  3 files changed, 12 insertions(+), 1 deletion(-)

I think if we replaced "MemEncryptSevLib" with "ResetVector" in the
subject line, that would be more precise. If a v3 becomes necessary,
please do that; otherwise I can do the update when I merge v2 (but even
if I forget that, it's not a big deal).

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

Thanks,
Laszlo

> 
> diff --git a/OvmfPkg/Include/Library/MemEncryptSevLib.h b/OvmfPkg/Include/Library/MemEncryptSevLib.h
> index dc09c61e58bb..a2c70aa550fe 100644
> --- a/OvmfPkg/Include/Library/MemEncryptSevLib.h
> +++ b/OvmfPkg/Include/Library/MemEncryptSevLib.h
> @@ -29,6 +29,8 @@ typedef struct _SEC_SEV_ES_WORK_AREA {
>    UINT8    Reserved1[7];
>  
>    UINT64   RandomData;
> +
> +  UINT64   EncryptionMask;
>  } SEC_SEV_ES_WORK_AREA;
>  
>  /**
> diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> index a1771dfdec23..5fae8986d9da 100644
> --- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> +++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> @@ -145,7 +145,7 @@ GetSevEncBit:
>  
>      ; The encryption bit position is always above 31
>      sub       ebx, 32
> -    jns       SevExit
> +    jns       SevSaveMask
>  
>      ; Encryption bit was reported as 31 or below, enter a HLT loop
>  SevEncBitLowHlt:
> @@ -153,6 +153,14 @@ SevEncBitLowHlt:
>      hlt
>      jmp       SevEncBitLowHlt
>  
> +SevSaveMask:
> +    xor       edx, edx
> +    bts       edx, ebx
> +
> +    mov       dword[SEV_ES_WORK_AREA_ENC_MASK], 0
> +    mov       dword[SEV_ES_WORK_AREA_ENC_MASK + 4], edx
> +    jmp       SevExit
> +
>  NoSev:
>      ;
>      ; Perform an SEV-ES sanity check by seeing if a #VC exception occurred.
> diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
> index d3aa87982959..5fbacaed5f9d 100644
> --- a/OvmfPkg/ResetVector/ResetVector.nasmb
> +++ b/OvmfPkg/ResetVector/ResetVector.nasmb
> @@ -74,6 +74,7 @@
>    %define GHCB_SIZE (FixedPcdGet32 (PcdOvmfSecGhcbSize))
>    %define SEV_ES_WORK_AREA (FixedPcdGet32 (PcdSevEsWorkAreaBase))
>    %define SEV_ES_WORK_AREA_RDRAND (FixedPcdGet32 (PcdSevEsWorkAreaBase) + 8)
> +  %define SEV_ES_WORK_AREA_ENC_MASK (FixedPcdGet32 (PcdSevEsWorkAreaBase) + 16)
>    %define SEV_ES_VC_TOP_OF_STACK (FixedPcdGet32 (PcdOvmfSecPeiTempRamBase) + FixedPcdGet32 (PcdOvmfSecPeiTempRamSize))
>  %include "Ia32/Flat32ToFlat64.asm"
>  %include "Ia32/PageTables64.asm"
>