ArmPkg/UncachedMemoryAllocationLib: map uncached allocations non-executable

The primary use case for UncachedMemoryAllocationLib is non-coherent DMA,
which implies that such regions are not used to fetch instructions from.

So let's map them as non-executable, to avoid creating a security hole
when the rest of the platform may be enforcing strict memory permissions
on ordinary allocations.

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/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.c

@@ -154,7 +154,8 @@ AllocatePagesFromList (
     return Status;
   }
 
-  Status = gDS->SetMemorySpaceAttributes (Memory, EFI_PAGES_TO_SIZE (Pages), EFI_MEMORY_WC);
+  Status = gDS->SetMemorySpaceAttributes (Memory, EFI_PAGES_TO_SIZE (Pages),
+                  EFI_MEMORY_WC | EFI_MEMORY_XP);
   if (EFI_ERROR (Status)) {
     gBS->FreePages (Memory, Pages);
     return Status;