Re: [PATCH v3 03/11] arm64: Consider stack randomization for mmap base only when necessary

[Kees Cook]

On Wed, Apr 17, 2019 at 12:26 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
>
> Do not offset mmap base address because of stack randomization if
> current task does not want randomization.

Maybe mention that this makes this logic match the existing x86 behavior too?

> Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  arch/arm64/mm/mmap.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index ed4f9915f2b8..ac89686c4af8 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -65,7 +65,11 @@ unsigned long arch_mmap_rnd(void)
>  static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>  {
>         unsigned long gap = rlim_stack->rlim_cur;
> -       unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
> +       unsigned long pad = stack_guard_gap;
> +
> +       /* Account for stack randomization if necessary */
> +       if (current->flags & PF_RANDOMIZE)
> +               pad += (STACK_RND_MASK << PAGE_SHIFT);
>
>         /* Values close to RLIM_INFINITY can overflow. */
>         if (gap + pad > gap)
> --
> 2.20.1
>


-- 
Kees Cook