ArmPkg/ArmMmuLib ARM: handle unmapped section in GetMemoryRegion()

GetMemoryRegion() is used to obtain the attributes of an existing
mapping, to permit permission attribute changes to be optimized
away if the attributes don't actually change.

The current ARM code assumes that a section mapping or a page mapping
exists for any region passed into GetMemoryRegion(), but the region
may be unmapped entirely, in which case the code will crash. So check
if a section mapping exists before dereferencing it.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

diff --git a/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c b/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c
index 12ca5b26673e834932e5a522d5e8b1e48943df39..3b29d33d0a9cb8ab89d5198115eb57e824043e54 100644 (file)
--- a/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c
+++ b/ArmPkg/Drivers/CpuDxe/Arm/Mmu.c
@@ -457,6 +457,9 @@ GetMemoryRegion (
 \r
   // Get the section at the given index\r
   SectionDescriptor = FirstLevelTable[TableIndex];\r
+  if (!SectionDescriptor) {\r
+    return EFI_NOT_FOUND;\r
+  }\r
 \r
   // If 'BaseAddress' belongs to the section then round it to the section boundary\r
   if (((SectionDescriptor & TT_DESCRIPTOR_SECTION_TYPE_MASK) == TT_DESCRIPTOR_SECTION_TYPE_SECTION) ||\r