ArmPkg/ArmMmuLib ARM: fix thinko in second level page table handling

PopulateLevel2PageTable () is invoked for [parts of] mappings that
start or end on a non-1 MB aligned address (or both). The size of
the mapping depends on both the start address modulo 1 MB and the
length of the mapping, but the logic that calculates this size is
flawed: subtracting 'start address modulo 1 MB' could result in a
negative value for the remaining length, which is obviously wrong.

So instead, take either RemainLength, or the rest of the 1 MB
block, whichever is smaller.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Tested-by: Eugene Cohen <eugene@hp.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
index b237321a8d..3b3b20aa9b 100644
--- a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
@@ -294,8 +294,8 @@ FillTranslationTable (
       PhysicalBase += TT_DESCRIPTOR_SECTION_SIZE;

       RemainLength -= TT_DESCRIPTOR_SECTION_SIZE;

     } else {

-      PageMapLength = MIN (RemainLength, TT_DESCRIPTOR_SECTION_SIZE) -

-                      (PhysicalBase % TT_DESCRIPTOR_SECTION_SIZE);

+      PageMapLength = MIN (RemainLength, TT_DESCRIPTOR_SECTION_SIZE -

+                                         (PhysicalBase % TT_DESCRIPTOR_SECTION_SIZE));

 

       // Case: Physical address aligned on the Section Size (1MB) && the length

       //       does not fill a section