[edk2-platforms][PATCH v1 1/1] MinPlatformPkg: Add Mem Type Info variable validity checks

["Michael Kubacki" <mikuback@linux.microsoft.com>]

From: Michael Kubacki <michael.kubacki@microsoft.com>

Adds some sanity checks around the Memory Type Information data
restored from the `EFI_MEMORY_TYPE_INFORMATION_VARIABLE_NAME` UEFI
variable.

This is particularly useful when the structures that the data was
saved against have changed in the latest firmware image. For example,
`EfiUnacceptedMemoryType` was added to `EFI_MEMORY_TYPE` in
edk2 commit `502c01c`. This incremented `EfiMaxMemoryType` by `1`.

That change was first released in the `edk2-stable202211` stable tag.

Firmware performing an update across those stable tags may encounter
issues depending on code implementation for handling
`EfiMaxMemoryType` as a terminating loop value. This change checks
the size and max memory type saved in the UEFI variable to determine
whether it is better to start from the defaults and rebuild the
UEFI variable data on the current boot.

Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Isaac Oram <isaac.w.oram@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Eric Dong <eric.dong@intel.com>
Co-authored-by: Ken Lautner <klautner@microsoft.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
---
 Platform/Intel/MinPlatformPkg/PlatformInit/PlatformInitPei/PlatformInitPreMem.c | 32 +++++++++++++++++---
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/Platform/Intel/MinPlatformPkg/PlatformInit/PlatformInitPei/PlatformInitPreMem.c b/Platform/Intel/MinPlatformPkg/PlatformInit/PlatformInitPei/PlatformInitPreMem.c
index d8c96b52f4b3..bc97711a02f6 100644
--- a/Platform/Intel/MinPlatformPkg/PlatformInit/PlatformInitPei/PlatformInitPreMem.c
+++ b/Platform/Intel/MinPlatformPkg/PlatformInit/PlatformInitPei/PlatformInitPreMem.c
@@ -164,18 +164,22 @@ BuildMemoryTypeInformation (
   EFI_STATUS                      Status;
   EFI_PEI_READ_ONLY_VARIABLE2_PPI *VariableServices;
   UINTN                           DataSize;
+  UINTN                           Index;
   EFI_MEMORY_TYPE_INFORMATION     MemoryData[EfiMaxMemoryType + 1];
 
   //
   // Locate system configuration variable
   //
-  Status = PeiServicesLocatePpi(
+  Status = PeiServicesLocatePpi (
              &gEfiPeiReadOnlyVariable2PpiGuid, // GUID
              0,                                // INSTANCE
              NULL,                             // EFI_PEI_PPI_DESCRIPTOR
              (VOID **) &VariableServices       // PPI
              );
-  ASSERT_EFI_ERROR(Status);
+  if (EFI_ERROR (Status)) {
+    ASSERT_EFI_ERROR (Status);
+    return;
+  }
 
   DataSize = sizeof (MemoryData);
   Status = VariableServices->GetVariable (
@@ -186,9 +190,29 @@ BuildMemoryTypeInformation (
                                &DataSize,
                                &MemoryData
                                );
-  if (EFI_ERROR(Status)) {
+  if (!EFI_ERROR (Status)) {
+    if (DataSize % sizeof (EFI_MEMORY_TYPE_INFORMATION) != 0) {
+      DEBUG ((DEBUG_ERROR, "The UEFI Memory Type Information variable size is inconsistent with this build.\n"));
+      Status = EFI_COMPROMISED_DATA;
+    } else {
+      // Loop through all except the last one and make sure it seems reasonable
+      for (Index = 0; Index < ((DataSize / sizeof (EFI_MEMORY_TYPE_INFORMATION)) - 1); Index++) {
+        if (MemoryData[Index].Type >= EfiMaxMemoryType) {
+          DEBUG ((DEBUG_ERROR, "UEFI Memory Type Information variable has an invalid memory type.\n"));
+          Status = EFI_COMPROMISED_DATA;
+        }
+      }
+      // The last entry must be MaxMemoryType with size 0
+      if ((MemoryData[Index].Type != EfiMaxMemoryType) || (MemoryData[Index].NumberOfPages != 0)) {
+        DEBUG ((DEBUG_ERROR, "UEFI Memory Type Information variable contains an invalid last entry.\n"));
+        Status = EFI_COMPROMISED_DATA;
+      }
+    }
+  }
+
+  if (EFI_ERROR (Status)) {
     DataSize = sizeof (mDefaultMemoryTypeInformation);
-    CopyMem(MemoryData, mDefaultMemoryTypeInformation, DataSize);
+    CopyMem (MemoryData, mDefaultMemoryTypeInformation, DataSize);
   }
 
   ///
-- 
2.41.0.windows.1