Re: [PATCH RFC v3 05/22] OvmfPkg: reserve Secrets page in MEMFD

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

On 06/07/21 14:26, Laszlo Ersek wrote:
> On 05/27/21 01:11, Brijesh Singh wrote:
>> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275
>>
>> When AMD SEV is enabled in the guest VM, a hypervisor need to insert a
>> secrets page.
>
> For pure SEV?
>
>>
>> When SEV-SNP is enabled, the secrets page contains the VM platform
>> communication keys. The guest BIOS and OS can use this key to communicate
>> with the SEV firmware to get attesation report. See the SEV-SNP firmware
>> spec for more details for the content of the secrets page.
>>
>> When SEV and SEV-ES is enabled, the secrets page contains the information
>> provided by the guest owner after the attestation. See the SEV
>> LAUNCH_SECRET command for more details.
>>
>> Cc: James Bottomley <jejb@linux.ibm.com>
>> Cc: Min Xu <min.m.xu@intel.com>
>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: Erdem Aktas <erdemaktas@google.com>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
>>  OvmfPkg/OvmfPkgX64.dsc                 |  2 ++
>>  OvmfPkg/OvmfPkgX64.fdf                 |  5 +++++
>>  OvmfPkg/AmdSev/SecretPei/SecretPei.inf |  1 +
>>  OvmfPkg/AmdSev/SecretPei/SecretPei.c   | 15 ++++++++++++++-
>>  4 files changed, 22 insertions(+), 1 deletion(-)
>
> How is all of the above related to the "OvmfPkg/OvmfPkgX64.dsc"
> platform, where remote attestation is not a goal?
>
> What you describe makes sense to me, but only for the remote-attested
> "OvmfPkg/AmdSev/AmdSevX64.dsc" platform. (Which already includes
> SecretPei and SecretDxe, and sets the necessary PCDs.)
>
> Then, even if we limit this patch only to the "OvmfPkg/AmdSev/SecretPei"
> module, the commit message does not explain sufficiently why the secrets
> page must be reserved for good. The "SEV-SNP firmware spec" reference is
> vague at best; I'm permanently lost between the dozen PDF files I have
> downloaded locally from the AMD website. Please include a specific
> document number, revision number, and chapter/section identifier.
>
> Honestly I'm getting a *rushed* vibe on this whole series. Why is that?
>
> Assume that I'm dumb. You won't be far from the truth. Then hold my hand
> through all this?

Here's the v2 discussion:

- http://mid.mail-archive.com/9804ecb5-8afd-c56e-4982-d1a6ebad3de8@redhat.com
- https://edk2.groups.io/g/devel/message/74797
- https://listman.redhat.com/archives/edk2-devel-archive/2021-May/msg00112.html

That discussion refers to a different use case, raised by Dov. That use
case might justify reserving the area even for plain SEV. It's out of
scope for now, AIUI.

(

And even for that separate use case, James showed down-thread that *not*
reserving the page forever in the firmware is more flexible.

- http://mid.mail-archive.com/aed7d3490fe6edee74440ed8e4cd5364fb2ba4af.camel@linux.ibm.com
- https://edk2.groups.io/g/devel/message/74801
- https://listman.redhat.com/archives/edk2-devel-archive/2021-May/msg00116.html

)

AFAICT, the only effect of the v2 sub-thread on the patch has been that
we now use the Reserved memory type rather than AcpiNVS (when SEV-SNP is
in use). I have two comments on that:

- It's good that we're not mixing in the other use case raised by Dov
  (i.e., enabling the guest-kernel to read secrets from the injected
  page even under plain SEV).

- It's still unclear to me why the reservation needs to be permanent
  under SEV-SNP.

Thanks
Laszlo

>>
>> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
>> index 999738dc39cd..ea08e1fabc65 100644
>> --- a/OvmfPkg/OvmfPkgX64.dsc
>> +++ b/OvmfPkg/OvmfPkgX64.dsc
>> @@ -716,6 +716,7 @@ [Components]
>>    OvmfPkg/SmmAccess/SmmAccessPei.inf
>>  !endif
>>    UefiCpuPkg/CpuMpPei/CpuMpPei.inf
>> +  OvmfPkg/AmdSev/SecretPei/SecretPei.inf
>>
>>  !if $(TPM_ENABLE) == TRUE
>>    OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
>> @@ -966,6 +967,7 @@ [Components]
>>    OvmfPkg/PlatformDxe/Platform.inf
>>    OvmfPkg/AmdSevDxe/AmdSevDxe.inf
>>    OvmfPkg/IoMmuDxe/IoMmuDxe.inf
>> +  OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf
>>
>>  !if $(SMM_REQUIRE) == TRUE
>>    OvmfPkg/SmmAccess/SmmAccess2Dxe.inf
>> diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
>> index d6be798fcadd..9126b8eb5014 100644
>> --- a/OvmfPkg/OvmfPkgX64.fdf
>> +++ b/OvmfPkg/OvmfPkgX64.fdf
>> @@ -88,6 +88,9 @@ [FD.MEMFD]
>>  0x00C000|0x001000
>>  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupSize
>>
>> +0x00D000|0x001000
>> +gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase|gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize
>> +
>>  0x010000|0x010000
>>  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
>>
>> @@ -179,6 +182,7 @@ [FV.PEIFV]
>>  INF  SecurityPkg/Tcg/TcgPei/TcgPei.inf
>>  INF  SecurityPkg/Tcg/Tcg2Pei/Tcg2Pei.inf
>>  !endif
>> +INF  OvmfPkg/AmdSev/SecretPei/SecretPei.inf
>>
>>  ################################################################################
>>
>> @@ -314,6 +318,7 @@ [FV.DXEFV]
>>  INF  ShellPkg/Application/Shell/Shell.inf
>>
>>  INF MdeModulePkg/Logo/LogoDxe.inf
>> +INF OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf
>>
>>  #
>>  # Network modules
>> diff --git a/OvmfPkg/AmdSev/SecretPei/SecretPei.inf b/OvmfPkg/AmdSev/SecretPei/SecretPei.inf
>> index 08be156c4bc0..9265f8adee12 100644
>> --- a/OvmfPkg/AmdSev/SecretPei/SecretPei.inf
>> +++ b/OvmfPkg/AmdSev/SecretPei/SecretPei.inf
>> @@ -26,6 +26,7 @@ [LibraryClasses]
>>    HobLib
>>    PeimEntryPoint
>>    PcdLib
>> +  MemEncryptSevLib
>>
>>  [FixedPcd]
>>    gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase
>> diff --git a/OvmfPkg/AmdSev/SecretPei/SecretPei.c b/OvmfPkg/AmdSev/SecretPei/SecretPei.c
>> index ad491515dd5d..51eb094555aa 100644
>> --- a/OvmfPkg/AmdSev/SecretPei/SecretPei.c
>> +++ b/OvmfPkg/AmdSev/SecretPei/SecretPei.c
>> @@ -7,6 +7,7 @@
>>  #include <PiPei.h>
>>  #include <Library/HobLib.h>
>>  #include <Library/PcdLib.h>
>> +#include <Library/MemEncryptSevLib.h>
>>
>>  EFI_STATUS
>>  EFIAPI
>> @@ -15,10 +16,22 @@ InitializeSecretPei (
>>    IN CONST EFI_PEI_SERVICES     **PeiServices
>>    )
>>  {
>> +  UINTN   Type;
>> +
>> +  //
>> +  // The location of the secret page should be marked reserved so that guest OS
>> +  // does not treated as a system RAM.
>> +  //
>> +  if (MemEncryptSevSnpIsEnabled ()) {
>> +    Type = EfiReservedMemoryType;
>> +  } else {
>> +    Type = EfiBootServicesData;
>> +  }
>> +
>>    BuildMemoryAllocationHob (
>>      PcdGet32 (PcdSevLaunchSecretBase),
>>      PcdGet32 (PcdSevLaunchSecretSize),
>> -    EfiBootServicesData
>> +    Type
>>      );
>>
>>    return EFI_SUCCESS;
>>
>