OvmfPkg/AmdSev: Enforce hash verification of kernel blobs

In the AmdSevX64 build, use BlobVerifierLibSevHashes to enforce
verification of hashes of the kernel/initrd/cmdline blobs fetched from
firmware config.

This allows for secure (measured) boot of SEV guests with QEMU's
-kernel/-initrd/-append switches (with the corresponding QEMU support
for injecting the hashes table into initial measured guest memory).

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ashish Kalra <ashish.kalra@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

OvmfPkg/AmdSev/AmdSevX64.dsc

@@ -173,7 +173,7 @@
   LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxBaseLib.inf
   CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf
   FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf
-  BlobVerifierLib|OvmfPkg/Library/BlobVerifierLibNull/BlobVerifierLibNull.inf
+  BlobVerifierLib|OvmfPkg/AmdSev/BlobVerifierLibSevHashes/BlobVerifierLibSevHashes.inf
 
 !if $(SOURCE_DEBUG_ENABLE) == TRUE
   PeCoffExtraActionLib|SourceLevelDebugPkg/Library/PeCoffExtraActionLibDebug/PeCoffExtraActionLibDebug.inf
@@ -696,7 +696,7 @@
   }
   OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.inf {
     <LibraryClasses>
-      NULL|OvmfPkg/Library/BlobVerifierLibNull/BlobVerifierLibNull.inf
+      NULL|OvmfPkg/AmdSev/BlobVerifierLibSevHashes/BlobVerifierLibSevHashes.inf
   }
   OvmfPkg/VirtioPciDeviceDxe/VirtioPciDeviceDxe.inf
   OvmfPkg/Virtio10Dxe/Virtio10.inf