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SubjectRe: [PATCH v3 06/11] arm: Use STACK_TOP when computing mmap base address
On Wed, Apr 17, 2019 at 12:29 AM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> mmap base address must be computed wrt stack top address, using TASK_SIZE
> is wrong since STACK_TOP and TASK_SIZE are not equivalent.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
> arch/arm/mm/mmap.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
> index bff3d00bda5b..0b94b674aa91 100644
> --- a/arch/arm/mm/mmap.c
> +++ b/arch/arm/mm/mmap.c
> @@ -19,7 +19,7 @@
>
> /* gap between mmap and stack */
> #define MIN_GAP (128*1024*1024UL)
> -#define MAX_GAP ((TASK_SIZE)/6*5)
> +#define MAX_GAP ((STACK_TOP)/6*5)

Parens around STACK_TOP aren't needed, but you'll be removing it
entirely, so I can't complain. ;)

> #define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))
>
> static int mmap_is_legacy(struct rlimit *rlim_stack)
> @@ -51,7 +51,7 @@ static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
> else if (gap > MAX_GAP)
> gap = MAX_GAP;
>
> - return PAGE_ALIGN(TASK_SIZE - gap - rnd);
> + return PAGE_ALIGN(STACK_TOP - gap - rnd);
> }
>
> /*
> --
> 2.20.1
>

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

--
Kees Cook

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