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SubjectRe: [PATCH v3 06/11] arm: Use STACK_TOP when computing mmap base address
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On 4/18/19 1:27 AM, Kees Cook wrote:
> On Wed, Apr 17, 2019 at 12:29 AM Alexandre Ghiti <alex@ghiti.fr> wrote:
>> mmap base address must be computed wrt stack top address, using TASK_SIZE
>> is wrong since STACK_TOP and TASK_SIZE are not equivalent.
>>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>> ---
>> arch/arm/mm/mmap.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
>> index bff3d00bda5b..0b94b674aa91 100644
>> --- a/arch/arm/mm/mmap.c
>> +++ b/arch/arm/mm/mmap.c
>> @@ -19,7 +19,7 @@
>>
>> /* gap between mmap and stack */
>> #define MIN_GAP (128*1024*1024UL)
>> -#define MAX_GAP ((TASK_SIZE)/6*5)
>> +#define MAX_GAP ((STACK_TOP)/6*5)
> Parens around STACK_TOP aren't needed, but you'll be removing it
> entirely, so I can't complain. ;)
>
>> #define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))
>>
>> static int mmap_is_legacy(struct rlimit *rlim_stack)
>> @@ -51,7 +51,7 @@ static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>> else if (gap > MAX_GAP)
>> gap = MAX_GAP;
>>
>> - return PAGE_ALIGN(TASK_SIZE - gap - rnd);
>> + return PAGE_ALIGN(STACK_TOP - gap - rnd);
>> }
>>
>> /*
>> --
>> 2.20.1
>>
> Acked-by: Kees Cook <keescook@chromium.org>


Thanks !

>

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