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SubjectRe: [PATCH] tile: support ASLR fully
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On Sat, Aug 10, 2013 at 6:55 PM, Jiri Kosina <jkosina@suse.cz> wrote:
> 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 <zlu@tilera.com>
>> Signed-off-by: Chris Metcalf <cmetcalf@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).

Looks like copy&paste from some other arch's implementation.
IMHO it's time to consolidate all the different but still mostly identical
arch_pick_mmap_layout() implementations.

>>
>> /*
>> * 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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--
Thanks,
//richard


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