MdeModulePkg: MAT Set RO/XP on Code/Data Sections Outside Image Memory

The Memory Attributes Table is generated by fetching the EFI memory map
and splitting entries which contain loaded images so DATA and CODE
sections have separate descriptors. The splitting is done via a call to
SplitTable() which
marks image DATA sections with the EFI_MEMORY_XP attribute and CODE
sections with the EFI_MEMORY_RO attribute when
splitting. After this process, there may still be EfiRuntimeServicesCode
regions which did not have their attributes set because they are not
part of loaded images.

This patch updates the MAT EnforceMemoryMapAttribute logic to set the
access attributes of runtime memory regions which are not part of loaded
images (have not had their access attributes set). The attributes of the
code regions will be read-only and no-execute because the UEFI spec
dictates that runtime code regions should only contain loaded EFI
modules.

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4832

Refs:
1.
https://edk2.groups.io/g/devel/topic/patch_v1_mdemodulepkg/105570114?p=,,,20,0,0,0::recentpostdate/sticky,,,20,2,0,105570114
2.
https://edk2.groups.io/g/devel/topic/mdemodulepkg_fix_mat/105477564?p=,,,20,0,0,0::recentpostdate/sticky,,,20,2,0,105477564

Signed-off-by: Oliver Smith-Denny <[email protected]>

MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c

@@ -447,16 +447,23 @@ EnforceMemoryMapAttribute (
   MemoryMapEntry = MemoryMap;
   MemoryMapEnd   = (EFI_MEMORY_DESCRIPTOR *)((UINT8 *)MemoryMap + MemoryMapSize);
   while ((UINTN)MemoryMapEntry < (UINTN)MemoryMapEnd) {
-    switch (MemoryMapEntry->Type) {
-      case EfiRuntimeServicesCode:
-        // do nothing
-        break;
-      case EfiRuntimeServicesData:
-        MemoryMapEntry->Attribute |= EFI_MEMORY_XP;
-        break;
-      case EfiReservedMemoryType:
-      case EfiACPIMemoryNVS:
-        break;
+    if ((MemoryMapEntry->Attribute & EFI_MEMORY_ACCESS_MASK) == 0) {
+      switch (MemoryMapEntry->Type) {
+        case EfiRuntimeServicesCode:
+          // If at this point the attributes have not been set on an EfiRuntimeServicesCode
+          // region, the memory range must not contain a loaded image. It's possible these
+          // non-image EfiRuntimeServicesCode regions are part of the unused memory bucket.
+          // It could also be that this region was explicitly allocated outside of the PE
+          // loader but the UEFI spec requires that all EfiRuntimeServicesCode regions contain
+          // EFI modules. In either case, set the attributes to RO and XP.
+          MemoryMapEntry->Attribute |= (EFI_MEMORY_RO | EFI_MEMORY_XP);
+          break;
+        case EfiRuntimeServicesData:
+          MemoryMapEntry->Attribute |= EFI_MEMORY_XP;
+          break;
+        default:
+          break;
+      }
     }
 
     MemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);