[RFC PATCH 15/19] OvmfPkg/PlatformPei: Validate the system RAM when SNP is active

["Brijesh Singh" <brijesh.singh@amd.com>]

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

When SEV-SNP is active, a memory region mapped encrypted in the page
table must be validated before access. There are two approaches that
can be taken to validate the system RAM detected during the PEI phase:

1) Validate on-demand
OR
2) Validate before access

On-demand
=========
If memory is not validated before access, it will cause a #VC
exception with the page-not-validated error code. The VC exception
handler can perform the validation steps.

The pages that have been validated will need to be tracked to avoid
the double validation scenarios. The range of memory that has not
been validated will need to be communicated to the OS through the
recently introduced unaccepted memory type
https://github.com/microsoft/mu_basecore/pull/66, so that OS can
validate those ranges before using them.

Validate before access
======================
Since the PEI phase detects all the available system RAM, use the
MemEncryptSevSnpValidateSystemRam() function to pre-validate the
system RAM in the PEI phase.

For now, we have chosen option 2 due to the dependency and the complexity
of the on-demand validation.

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>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/PlatformPei/AmdSev.c | 41 ++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
index 95c5ad235f..abbbef54c1 100644
--- a/OvmfPkg/PlatformPei/AmdSev.c
+++ b/OvmfPkg/PlatformPei/AmdSev.c
@@ -140,6 +140,42 @@ AmdSevEsInitialize (
   AsmWriteGdtr (&Gdtr);
 }
 
+/**
+
+  Initialize SEV-SNP support if running as an SEV-SNP guest.
+
+  **/
+STATIC
+VOID
+AmdSevSnpInitialize (
+  VOID
+  )
+{
+  EFI_PEI_HOB_POINTERS          Hob;
+  EFI_HOB_RESOURCE_DESCRIPTOR   *ResourceHob;
+
+  if (!MemEncryptSevSnpIsEnabled ()) {
+    return;
+  }
+
+  DEBUG ((EFI_D_INFO, "SEV-SNP is enabled.\n"));
+
+  //
+  // Iterate through the system RAM and validate it.
+  //
+  for (Hob.Raw = GetHobList (); !END_OF_HOB_LIST (Hob); Hob.Raw = GET_NEXT_HOB (Hob)) {
+    if (Hob.Raw != NULL && GET_HOB_TYPE (Hob) == EFI_HOB_TYPE_RESOURCE_DESCRIPTOR) {
+      ResourceHob = Hob.ResourceDescriptor;
+
+      if (ResourceHob->ResourceType == EFI_RESOURCE_SYSTEM_MEMORY) {
+        MemEncryptSevSnpValidateSystemRam (ResourceHob->PhysicalStart,
+                                           EFI_SIZE_TO_PAGES (ResourceHob->ResourceLength)
+                                          );
+      }
+    }
+  }
+}
+
 /**
 
   Function checks if SEV support is available, if present then it sets
@@ -217,6 +253,11 @@ AmdSevInitialize (
     }
   }
 
+  //
+  // Check and perform SEV-SNP initialization if required.
+  //
+  AmdSevSnpInitialize ();
+
   //
   // Check and perform SEV-ES initialization if required.
   //
-- 
2.17.1