[PATCH v2 3/4] ArmPkg/CpuDxe: ARM: ignore page table updates that only change permissions

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

Currently, we have not implemented support on 32-bit ARM for managing
permission bits in the page tables. Since the new DXE page protection
for PE/COFF images may invoke EFI_CPU_ARCH_PROTOCOL.SetMemoryAttributes()
with only permission attributes set, let's simply ignore those for now.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
---
 ArmPkg/Drivers/CpuDxe/Arm/Mmu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c b/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c
index b6ba975b353a..89e429925ba9 100644
--- a/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c
+++ b/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c
@@ -680,6 +680,13 @@ SetMemoryAttributes (
 {
   EFI_STATUS    Status;
 
+  //
+  // Ignore invocations that only modify permission bits
+  //
+  if ((Attributes & EFI_MEMORY_CACHETYPE_MASK) == 0) {
+    return EFI_SUCCESS;
+  }
+
   if(((BaseAddress & 0xFFFFF) == 0) && ((Length & 0xFFFFF) == 0)) {
     // Is the base and length a multiple of 1 MB?
     DEBUG ((EFI_D_PAGE, "SetMemoryAttributes(): MMU section 0x%x length 0x%x to %lx\n", (UINTN)BaseAddress, (UINTN)Length, Attributes));
-- 
2.7.4