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SubjectRe: [PATCH v4] x86: increase MIN_GAP to include randomized stack
On Tue, 8 Sep 2009, Michal Hocko wrote:

> Currently we are not including randomized stack size when calculating
> mmap_base address in arch_pick_mmap_layout for topdown case. This might
> cause that mmap_base starts in the stack reserved area because stack is
> randomized by 1GB for 64b (8MB for 32b) and the minimum gap is 128MB.
>
> If the stack really grows down to mmap_base then we can get silent mmap
> region overwrite by the stack values.
>
> Let's include maximum stack randomization size into MIN_GAP which is
> used as the low bound for the gap in mmap.
>
> Signed-off-by: Michal Hocko <mhocko@suse.cz>

Acked-by: Jiri Kosina <jkosina@suse.cz>

Ingo, could you please consider applying this?

> ---
> arch/x86/include/asm/elf.h | 2 ++
> arch/x86/mm/mmap.c | 17 +++++++++++++++--
> 2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> index 83c1bc8..456a304 100644
> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -299,6 +299,8 @@ do { \
>
> #ifdef CONFIG_X86_32
>
> +#define STACK_RND_MASK (0x7ff)
> +
> #define VDSO_HIGH_BASE (__fix_to_virt(FIX_VDSO))
>
> #define ARCH_DLINFO ARCH_DLINFO_IA32(vdso_enabled)
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 1658296..c8191de 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -29,13 +29,26 @@
> #include <linux/random.h>
> #include <linux/limits.h>
> #include <linux/sched.h>
> +#include <asm/elf.h>
> +
> +static unsigned int stack_maxrandom_size(void)
> +{
> + unsigned int max = 0;
> + if ((current->flags & PF_RANDOMIZE) &&
> + !(current->personality & ADDR_NO_RANDOMIZE)) {
> + max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
> + }
> +
> + return max;
> +}
> +
>
> /*
> * Top of mmap area (just below the process stack).
> *
> - * Leave an at least ~128 MB hole.
> + * Leave an at least ~128 MB hole with possible stack randomization.
> */
> -#define MIN_GAP (128*1024*1024)
> +#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
> #define MAX_GAP (TASK_SIZE/6*5)
>
> /*
> --
> 1.6.3.3
>

--
Jiri Kosina
SUSE Labs


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