BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

Platform features and capabilities are traditionally discovered via the
CPUID instruction. Hypervisors typically trap and emulate the CPUID
instruction for a variety of reasons. There are some cases where incorrect
CPUID information can potentially lead to a security issue. The SEV-SNP
firmware provides a feature to filter the CPUID results through the PSP.
The filtered CPUID values are saved on a special page for the guest to
consume. Reserve a page in MEMFD that will contain the results of
filtered CPUID values.

Add a new section in Ovmf metadata structure so that hypervisor can
locate and populate the CPUID values before the boot.

Cc: Michael Roth <michael.roth@...>
Cc: James Bottomley <jejb@...>
Cc: Min Xu <min.m.xu@...>
Cc: Jiewen Yao <jiewen.yao@...>
Cc: Tom Lendacky <thomas.lendacky@...>
Cc: Jordan Justen <jordan.l.justen@...>
Cc: Ard Biesheuvel <ardb+tianocore@...>
Cc: Erdem Aktas <erdemaktas@...>
Cc: Gerd Hoffmann <kraxel@...>
Acked-by: Jiewen Yao <Jiewen.yao@...>
Signed-off-by: Brijesh Singh <brijesh.singh@...>
---
OvmfPkg/OvmfPkg.dec | 7 +++++++
OvmfPkg/OvmfPkgX64.fdf | 3 +++
OvmfPkg/ResetVector/ResetVector.inf | 2 ++
OvmfPkg/ResetVector/ResetVector.nasmb | 2 ++
OvmfPkg/ResetVector/X64/OvmfMetadata.asm | 15 +++++++++++++++
5 files changed, 29 insertions(+)

diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec
index 6266fdef6054..efa0de6d0600 100644
--- a/OvmfPkg/OvmfPkg.dec
+++ b/OvmfPkg/OvmfPkg.dec
@@ -347,6 +347,13 @@ [PcdsFixedAtBuild]
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsBase|0|UINT32|0x52
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsSize|0|UINT32|0x53

+ ## The base address and size of a CPUID Area that contains the hypervisor
+ # provided CPUID results. In the case of SEV-SNP, the CPUID results are
+ # filtered by the SEV-SNP firmware. If this is set in the .fdf, the
+ # platform is responsible to reserve this area from DXE phase overwrites.
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidBase|0|UINT32|0x54
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidSize|0|UINT32|0x55
+
[PcdsDynamic, PcdsDynamicEx]
gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent|0|UINT64|2
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashVariablesEnable|FALSE|BOOLEAN|0x10
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index 5b871db20ab2..b38c123b8341 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -91,6 +91,9 @@ [FD.MEMFD]
0x00D000|0x001000
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsSize

+0x00E000|0x001000
+gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidSize
+
0x010000|0x010000
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize

diff --git a/OvmfPkg/ResetVector/ResetVector.inf b/OvmfPkg/ResetVector/ResetVector.inf
index 09454d0797e6..4cb81a3233f0 100644
--- a/OvmfPkg/ResetVector/ResetVector.inf
+++ b/OvmfPkg/ResetVector/ResetVector.inf
@@ -46,6 +46,8 @@ [Pcd]
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase

[FixedPcd]
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidBase
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidSize
gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase
gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize
gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableBase
diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
index f7d09acd33ed..84cb5ae81b66 100644
--- a/OvmfPkg/ResetVector/ResetVector.nasmb
+++ b/OvmfPkg/ResetVector/ResetVector.nasmb
@@ -79,6 +79,8 @@
%define SEV_ES_VC_TOP_OF_STACK (FixedPcdGet32 (PcdOvmfSecPeiTempRamBase) + FixedPcdGet32 (PcdOvmfSecPeiTempRamSize))
%define SEV_SNP_SECRETS_BASE (FixedPcdGet32 (PcdOvmfSnpSecretsBase))
%define SEV_SNP_SECRETS_SIZE (FixedPcdGet32 (PcdOvmfSnpSecretsSize))
+ %define CPUID_BASE (FixedPcdGet32 (PcdOvmfCpuidBase))
+ %define CPUID_SIZE (FixedPcdGet32 (PcdOvmfCpuidSize))

%include "Ia32/Flat32ToFlat64.asm"
%include "Ia32/AmdSev.asm"
diff --git a/OvmfPkg/ResetVector/X64/OvmfMetadata.asm b/OvmfPkg/ResetVector/X64/OvmfMetadata.asm
index bb348e1c6a79..3f4b017104fc 100644
--- a/OvmfPkg/ResetVector/X64/OvmfMetadata.asm
+++ b/OvmfPkg/ResetVector/X64/OvmfMetadata.asm
@@ -23,6 +23,15 @@ BITS 64
; The section must be accepted or validated by the VMM before the boot
%define OVMF_SECTION_TYPE_SEC_MEM 0x102

+;
+; The section contains the hypervisor pre-populated CPUID values.
+; In the case of SEV-SNP, the CPUID values are filtered and measured by
+; the SEV-SNP firmware.
+; The CPUID format is documented in SEV-SNP firmware spec 0.9 section 7.1
+; (CPUID function structure).
+;
+%define OVMF_SECTION_TYPE_CPUID 0x103
+
; AMD SEV-SNP specific sections
%define OVMF_SECTION_TYPE_SNP_SECRETS 0x200

@@ -50,5 +59,11 @@ SevSnpSecrets:
DD SEV_SNP_SECRETS_SIZE
DD OVMF_SECTION_TYPE_SNP_SECRETS

+; CPUID values
+CpuidSec:
+ DD CPUID_BASE
+ DD CPUID_SIZE
+ DD OVMF_SECTION_TYPE_CPUID
+
OvmfGuidedStructureEnd:
ALIGN 16
--
2.25.1