[PATCH v5 32/38] MdeModulePkg/DxeCore: Update memory protections before freeing a region

["Ard Biesheuvel" <ardb@kernel.org>]

Currently, we invoke ApplyMemoryProtectionPolicy() after
CoreInternalFreePages() has returned successfully, in order to update
the memory permission attributes of the region to match the policy for
EfiConventionalMemory.

There are two problems with that:
- CoreInternalFreePages() will round up the size of the allocation to
  the appropriate alignment of the memory type, but we only remap the
  number of pages that was passed by the caller, leaving the remaining
  pages freed but mapped with the old permissions;
- in DEBUG builds, we may attempt to clear the entire region while it is
  still mapped with read-only or read-protect attributes.

Let's address both issues, by updating the permissions before performing
the actual conversion.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 MdeModulePkg/Core/Dxe/Mem/Page.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/Mem/Page.c b/MdeModulePkg/Core/Dxe/Mem/Page.c
index 5903ce7ab525..f5b940bbc25b 100644
--- a/MdeModulePkg/Core/Dxe/Mem/Page.c
+++ b/MdeModulePkg/Core/Dxe/Mem/Page.c
@@ -1519,8 +1519,8 @@ CoreAllocatePages (
   @return EFI_SUCCESS         -Pages successfully freed.
 
 **/
+STATIC
 EFI_STATUS
-EFIAPI
 CoreInternalFreePages (
   IN EFI_PHYSICAL_ADDRESS  Memory,
   IN UINTN                 NumberOfPages,
@@ -1574,6 +1574,13 @@ CoreInternalFreePages (
   NumberOfPages += EFI_SIZE_TO_PAGES (Alignment) - 1;
   NumberOfPages &= ~(EFI_SIZE_TO_PAGES (Alignment) - 1);
 
+  ApplyMemoryProtectionPolicy (
+    Entry->Type,
+    EfiConventionalMemory,
+    Memory,
+    EFI_PAGES_TO_SIZE (NumberOfPages)
+    );
+
   if (MemoryType != NULL) {
     *MemoryType = Entry->Type;
   }
@@ -1628,12 +1635,6 @@ CoreFreePages (
       NULL
       );
     InstallMemoryAttributesTableOnMemoryAllocation (MemoryType);
-    ApplyMemoryProtectionPolicy (
-      MemoryType,
-      EfiConventionalMemory,
-      Memory,
-      EFI_PAGES_TO_SIZE (NumberOfPages)
-      );
   }
 
   return Status;
-- 
2.39.2