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SubjectRe: [PATCH v3 05/11] arm: Properly account for stack randomization and stack guard gap
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On 4/18/19 1:26 AM, Kees Cook wrote:
> On Wed, Apr 17, 2019 at 12:28 AM Alexandre Ghiti <alex@ghiti.fr> wrote:
>> This commit takes care of stack randomization and stack guard gap when
>> computing mmap base address and checks if the task asked for randomization.
>> This fixes the problem uncovered and not fixed for arm here:
>> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1429066.html
> Please use the official archive instead. This includes headers, linked
> patches, etc:
> https://lkml.kernel.org/r/20170622200033.25714-1-riel@redhat.com


Ok, sorry about that, and thanks for the info.


>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>> ---
>> arch/arm/mm/mmap.c | 14 ++++++++++++--
>> 1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
>> index f866870db749..bff3d00bda5b 100644
>> --- a/arch/arm/mm/mmap.c
>> +++ b/arch/arm/mm/mmap.c
>> @@ -18,8 +18,9 @@
>> (((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))
>>
>> /* gap between mmap and stack */
>> -#define MIN_GAP (128*1024*1024UL)
>> -#define MAX_GAP ((TASK_SIZE)/6*5)
>> +#define MIN_GAP (128*1024*1024UL)
> Might as well fix this up as SIZE_128M


I left the code as is because it gets removed in the next commit, I did not
even correct the checkpatch warnings. But I can fix that in v4, since there
will be a v4 :)


>
>> +#define MAX_GAP ((TASK_SIZE)/6*5)
>> +#define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))
> STACK_RND_MASK is already defined so you don't need to add it here, yes?


At this point, I don't think arm has STACK_RND_MASK defined anywhere since
the generic version is in mm/util.c.


>
>> static int mmap_is_legacy(struct rlimit *rlim_stack)
>> {
>> @@ -35,6 +36,15 @@ static int mmap_is_legacy(struct rlimit *rlim_stack)
>> static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>> {
>> unsigned long gap = rlim_stack->rlim_cur;
>> + unsigned long pad = stack_guard_gap;
>> +
>> + /* Account for stack randomization if necessary */
>> + if (current->flags & PF_RANDOMIZE)
>> + pad += (STACK_RND_MASK << PAGE_SHIFT);
>> +
>> + /* Values close to RLIM_INFINITY can overflow. */
>> + if (gap + pad > gap)
>> + gap += pad;
>>
>> if (gap < MIN_GAP)
>> gap = MIN_GAP;
>> --
>> 2.20.1
>>
> But otherwise, yes:
>
> Acked-by: Kees Cook <keescook@chromium.org>


Thanks !


>
> --
> Kees Cook
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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