From: Rik van Riel <riel@xxxxxxxxxx> Subject: arm64/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. Obtained from Daniel Micay's linux-hardened tree. Link: http://lkml.kernel.org/r/20170622200033.25714-3-riel@xxxxxxxxxx Signed-off-by: Daniel Micay <danielmicay@xxxxxxxxx> 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/arm64/mm/mmap.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff -puN arch/arm64/mm/mmap.c~arm64-mmap-properly-account-for-stack-randomization-in-mmap_base arch/arm64/mm/mmap.c --- a/arch/arm64/mm/mmap.c~arm64-mmap-properly-account-for-stack-randomization-in-mmap_base +++ a/arch/arm64/mm/mmap.c @@ -35,7 +35,7 @@ * Leave enough space between the mmap area and the stack to honour ulimit in * the face of randomisation. */ -#define MIN_GAP (SZ_128M + ((STACK_RND_MASK << PAGE_SHIFT) + 1)) +#define MIN_GAP (SZ_128M) #define MAX_GAP (STACK_TOP/6*5) static int mmap_is_legacy(void) @@ -65,6 +65,11 @@ unsigned long arch_mmap_rnd(void) static unsigned long mmap_base(unsigned long rnd) { unsigned long gap = rlimit(RLIMIT_STACK); + unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + 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
