From aa1097921d7581a8a9c527d5beb3d9d97c731f7e Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Fri, 30 Nov 2018 12:28:27 +0100
Subject: [PATCH] ArmPkg/ArmMmuLib ARM: handle unmapped sections when updating
 permissions

The ARM ArmMmuLib code currently does not take into account that
setting permissions on a region should take into account that a
region may not be mapped yet to begin with.

So when updating a section descriptor whose old value is zero,
pass in the address explicitly.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
---
 ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
index ec51e072ab..889b22867d 100644
--- a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
@@ -695,8 +695,12 @@ UpdateSectionEntries (
     } else {
       // still a section entry
 
-      // mask off appropriate fields
-      Descriptor = CurrentDescriptor & ~EntryMask;
+      if (CurrentDescriptor != 0) {
+        // mask off appropriate fields
+        Descriptor = CurrentDescriptor & ~EntryMask;
+      } else {
+        Descriptor = ((UINTN)FirstLevelIdx + i) << TT_DESCRIPTOR_SECTION_BASE_SHIFT;
+      }
 
       // mask in new attributes and/or permissions
       Descriptor |= EntryValue;