Re: [PATCH 2/2] ArmPkg/ArmMmuLib ARM: fix thinko in second level page table handling

[Leif Lindholm <leif.lindholm@linaro.org>]

On Fri, Jan 04, 2019 at 07:04:32PM +0100, Ard Biesheuvel wrote:
> 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>

> ---
>  ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
> index b237321a8d8b..3b3b20aa9b78 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
> -- 
> 2.17.1
>