OvmfPkg/SecMain: validate the memory used for decompressing Fv

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

The VMM launch sequence should have pre-validated all the data pages used
in the Reset vector. The range does not cover the data pages used during
the SEC phase (mainly PEI and DXE firmware volume decompression memory).

When SEV-SNP is active, the memory must be pre-validated before the access.
Add support to pre-validate the memory range from SnpSecPreValidatedStart
to SnpSecPreValidatedEnd. This should be sufficent to enter into the PEI
phase.

Cc: Michael Roth <michael.roth@amd.com>
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: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

OvmfPkg/FvmainCompactScratchEnd.fdf.inc

@@ -63,3 +63,8 @@ DEFINE DECOMP_SCRATCH_BASE_MASK      = 0xFFF00000
 DEFINE DECOMP_SCRATCH_BASE           = (($(DECOMP_SCRATCH_BASE_UNALIGNED) + $(DECOMP_SCRATCH_BASE_ALIGNMENT)) & $(DECOMP_SCRATCH_BASE_MASK))
 
 SET gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDecompressionScratchEnd = $(DECOMP_SCRATCH_BASE) + $(DECOMP_SCRATCH_SIZE)
+
+#
+# The range of pages that should be pre-validated during the SEC phase when SEV-SNP is active in the guest VM.
+SET gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedStart = $(MEMFD_BASE_ADDRESS) + gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase
+SET gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedEnd = $(DECOMP_SCRATCH_BASE) + $(DECOMP_SCRATCH_SIZE)

OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf

@@ -60,3 +60,5 @@
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedEnd
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedStart

OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c

@@ -29,6 +29,11 @@ STATIC SNP_PRE_VALIDATED_RANGE  mPreValidatedRange[] = {
     FixedPcdGet32 (PcdOvmfSecPageTablesBase),
     FixedPcdGet32 (PcdOvmfPeiMemFvBase),
   },
+  // The below range is pre-validated by the Sec/SecMain.c
+  {
+    FixedPcdGet32 (PcdOvmfSecValidatedStart),
+    FixedPcdGet32 (PcdOvmfSecValidatedEnd)
+  },
 };
 
 STATIC

OvmfPkg/OvmfPkg.dec

@@ -364,6 +364,10 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidBase|0|UINT32|0x60
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidSize|0|UINT32|0x61
 
+  ## The range of memory that is validated by the SEC phase.
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedStart|0|UINT32|0x62
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedEnd|0|UINT32|0x63
+
 [PcdsDynamic, PcdsDynamicEx]
   gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent|0|UINT64|2
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashVariablesEnable|FALSE|BOOLEAN|0x10

OvmfPkg/Sec/AmdSev.c

@@ -55,7 +55,6 @@ SevEsProtocolFailure (
   @retval FALSE  SEV-SNP is not enabled
 
 **/
-STATIC
 BOOLEAN
 SevSnpIsEnabled (
   VOID
@@ -281,3 +280,24 @@ SevEsIsEnabled (
 
   return (SevEsWorkArea->SevEsEnabled != 0);
 }
+
+/**
+ Validate System RAM used for decompressing the PEI and DXE firmware volumes
+ when SEV-SNP is active. The PCDs SecValidatedStart and SecValidatedEnd are
+ set in OvmfPkg/FvmainCompactScratchEnd.fdf.inc.
+
+**/
+VOID
+SecValidateSystemRam (
+  VOID
+  )
+{
+  PHYSICAL_ADDRESS  Start, End;
+
+  if (IsSevGuest () && SevSnpIsEnabled ()) {
+    Start = (EFI_PHYSICAL_ADDRESS)(UINTN)PcdGet32 (PcdOvmfSecValidatedStart);
+    End   = (EFI_PHYSICAL_ADDRESS)(UINTN)PcdGet32 (PcdOvmfSecValidatedEnd);
+
+    MemEncryptSevSnpPreValidateSystemRam (Start, EFI_SIZE_TO_PAGES ((UINTN)(End - Start)));
+  }
+}

OvmfPkg/Sec/AmdSev.h

@@ -68,4 +68,27 @@ SevEsIsEnabled (
   VOID
   );
 
+/**
+ Validate System RAM used for decompressing the PEI and DXE firmware volumes
+ when SEV-SNP is active. The PCDs SecValidatedStart and SecValidatedEnd are
+ set in OvmfPkg/FvmainCompactScratchEnd.fdf.inc.
+
+**/
+VOID
+SecValidateSystemRam (
+  VOID
+  );
+
+/**
+  Determine if SEV-SNP is active.
+
+  @retval TRUE   SEV-SNP is enabled
+  @retval FALSE  SEV-SNP is not enabled
+
+**/
+BOOLEAN
+SevSnpIsEnabled (
+  VOID
+  );
+
 #endif

OvmfPkg/Sec/SecMain.c

@@ -860,6 +860,11 @@ SecCoreStartupWithStack (
   SecCoreData.BootFirmwareVolumeBase = BootFv;
   SecCoreData.BootFirmwareVolumeSize = (UINTN)BootFv->FvLength;
 
+  //
+  // Validate the System RAM used in the SEC Phase
+  //
+  SecValidateSystemRam ();
+
   //
   // Make sure the 8259 is masked before initializing the Debug Agent and the debug timer is enabled
   //

OvmfPkg/Sec/SecMain.inf

@@ -52,6 +52,7 @@
   PeCoffExtraActionLib
   ExtractGuidedSectionLib
   LocalApicLib
+  MemEncryptSevLib
   CpuExceptionHandlerLib
 
 [Ppis]
@@ -74,6 +75,8 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdInitValueInTempStack
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfConfidentialComputingWorkAreaHeader
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedStart
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedEnd
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire