From: Rik van Riel <riel@xxxxxxxxxx> Subject: powerpc,mmap: properly account for stack randomization in mmap_base When RLIMIT_STACK is, for example, 256MB, the current code results in a gap between the top of the task and mmap_base of 256MB, failing to take into account the amount by which the stack address was randomized. In other words, the stack gets less than RLIMIT_STACK space. Ensure that the gap between the stack and mmap_base always takes stack randomization and the stack guard gap into account. Inspired by Daniel Micay's linux-hardened tree. Link: http://lkml.kernel.org/r/20170622200033.25714-4-riel@xxxxxxxxxx Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> Reported-by: Florian Weimer <fweimer@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: Daniel Micay <danielmicay@xxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/powerpc/mm/mmap.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) diff -puN arch/powerpc/mm/mmap.c~powerpcmmap-properly-account-for-stack-randomization-in-mmap_base arch/powerpc/mm/mmap.c --- a/arch/powerpc/mm/mmap.c~powerpcmmap-properly-account-for-stack-randomization-in-mmap_base +++ a/arch/powerpc/mm/mmap.c @@ -34,16 +34,9 @@ /* * Top of mmap area (just below the process stack). * - * Leave at least a ~128 MB hole on 32bit applications. - * - * On 64bit applications we randomise the stack by 1GB so we need to - * space our mmap start address by a further 1GB, otherwise there is a - * chance the mmap area will end up closer to the stack than our ulimit - * requires. + * Leave at least a ~128 MB hole. */ -#define MIN_GAP32 (128*1024*1024) -#define MIN_GAP64 ((128 + 1024)*1024*1024UL) -#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64) +#define MIN_GAP (128*1024*1024) #define MAX_GAP (TASK_SIZE/6*5) static inline int mmap_is_legacy(void) @@ -71,9 +64,26 @@ unsigned long arch_mmap_rnd(void) return rnd << PAGE_SHIFT; } +static inline unsigned long stack_maxrandom_size(void) +{ + if (!(current->flags & PF_RANDOMIZE)) + return 0; + + /* 8MB for 32bit, 1GB for 64bit */ + if (is_32bit_task()) + return (1<<23); + else + return (1<<30); +} + static inline unsigned long mmap_base(unsigned long rnd) { unsigned long gap = rlimit(RLIMIT_STACK); + unsigned long pad = stack_maxrandom_size() + stack_guard_gap; + + /* Values close to RLIM_INFINITY can overflow. */ + if (gap + pad > gap) + gap += pad; if (gap < MIN_GAP) gap = MIN_GAP; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
