From c204d21f2232d875e36b8774c36ffd027dc1d606 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 12 Jul 2017 14:36:33 -0700 Subject: [PATCH] x86/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/20170622200033.25714-2-riel@redhat.com Signed-off-by: Daniel Micay Signed-off-by: Rik van Riel Reported-by: Florian Weimer Acked-by: Ingo Molnar Cc: Will Deacon Cc: Daniel Micay Cc: Benjamin Herrenschmidt Cc: Hugh Dickins Cc: Catalin Marinas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/x86/mm/mmap.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c index 797295e792b2..229d04a83f85 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -92,13 +92,18 @@ unsigned long arch_mmap_rnd(void) static unsigned long mmap_base(unsigned long rnd, unsigned long task_size) { unsigned long gap = rlimit(RLIMIT_STACK); + unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap; unsigned long gap_min, gap_max; + /* Values close to RLIM_INFINITY can overflow. */ + if (gap + pad > gap) + gap += pad; + /* * Top of mmap area (just below the process stack). * Leave an at least ~128 MB hole with possible stack randomization. */ - gap_min = SIZE_128M + stack_maxrandom_size(task_size); + gap_min = SIZE_128M; gap_max = (task_size / 6) * 5; if (gap < gap_min) -- 2.20.1