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SubjectRe: [PATCH v3] 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>
> ---
> arch/x86/mm/mmap.c | 25 +++++++++++++++++++++++--
> 1 files changed, 23 insertions(+), 2 deletions(-)
>
> I think that this is also stable material and I will repost it to
> stable@kernel.org once you ack it.
>
> Changes from v2:
> STACK_RND_MASK has to be defined for CONFIG_X86_32 as well.
>
> Changes from v1:
> Fixed unsigned int overflow in MIN_GAP calculation.
>
>
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 1658296..a4566a8 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -30,12 +30,33 @@
> #include <linux/limits.h>
> #include <linux/sched.h>
>
> +/* 1GB for 64bit, 8MB for 32bit definition taken from arch/x86/include/asm/elf.h */
> +#ifndef STACK_RND_MASK
> +#ifdef CONFIG_X86_64
> +#define STACK_RND_MASK (test_thread_flag(TIF_IA32) ? 0x7ff : 0x3fffff)
> +#else
> +#define STACK_RND_MASK (0x7ff)
> +#endif
> +#endif

I'd still prefer all this macro-magic happening in <asm/elf.h> and
including this file from arch/x86/mm/mmap.c, otherwise we are duplicating
the STACK_RND_MASK definition, which is messy.

--
Jiri Kosina
SUSE Labs


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