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SubjectRe: [PATCH v3 03/11] arm64: Consider stack randomization for mmap base only when necessary
On Wed, Apr 17, 2019 at 12:26 AM Alexandre Ghiti <alex@ghiti.fr> 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@ghiti.fr>

Acked-by: Kees Cook <keescook@chromium.org>

-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

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