On Fri, 9 Aug 2013, Tony Lu wrote:
> With this change, tile Linux now supports address-space layout
> randomization for shared objects, stack, heap and vdso.
>
> Signed-off-by: Tony Lu <z...@tilera.com>
> Signed-off-by: Chris Metcalf <cmetc...@tilera.com>
> ---
> arch/tile/include/asm/elf.h | 4 ++++
> arch/tile/mm/mmap.c | 20 ++++++++++++++++++--
> 2 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/arch/tile/include/asm/elf.h b/arch/tile/include/asm/elf.h
> index 31d854f..e1da88e 100644
> --- a/arch/tile/include/asm/elf.h
> +++ b/arch/tile/include/asm/elf.h
> @@ -137,6 +137,10 @@ do { \
> NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_BASE); \
> } while (0)
>
> +struct mm_struct;
> +extern unsigned long arch_randomize_brk(struct mm_struct *mm);
> +#define arch_randomize_brk arch_randomize_brk
> +
> #ifdef CONFIG_COMPAT
>
> #define COMPAT_ELF_PLATFORM "tilegx-m32"
> diff --git a/arch/tile/mm/mmap.c b/arch/tile/mm/mmap.c
> index d67d91e..b3686ce 100644
> --- a/arch/tile/mm/mmap.c
> +++ b/arch/tile/mm/mmap.c
> @@ -58,16 +58,32 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
> #else
> int is_32bit = 0;
> #endif
> + unsigned long random_factor = 0UL;
> +
> + if (current->flags & PF_RANDOMIZE) {
> + random_factor = get_random_int();
> + random_factor = random_factor << PAGE_SHIFT;
> + if (is_32bit)
> + random_factor &= 0xfffffful;
> + else
> + random_factor &= 0xffffffful;
> + }
Hi Tony,
to me, the used math seems not to be immediatley understandable on a first
sight. Instead of using full range of get_random_int() and then clamping
it by anding with 0xffffffUL or fffffffUL, how about just using
appropriate division reminder to the result of get_random_int()? (for
inspiration and for understanding of what I mean, please see what
mmap_rnd() is doing on x86).
>
> /*
> * Use standard layout if the expected stack growth is unlimited
> * or we are running native 64 bits.
> */
> - if (!is_32bit || rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
> - mm->mmap_base = TASK_UNMAPPED_BASE;
> + if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
> + mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
> mm->get_unmapped_area = arch_get_unmapped_area;
> } else {
> mm->mmap_base = mmap_base(mm);
> mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> }
> }
> +
> +unsigned long arch_randomize_brk(struct mm_struct *mm)
> +{
> + unsigned long range_end = mm->brk + 0x02000000;
> + return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
> +}
Otherwise the patch looks good to me, so once you either add some
explanatory comment to the get_random_int() math, or convert it to use
division reminder, I'll be happy to Ack it.
Thanks,
--
Jiri Kosina
SUSE Labs
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