From c204d21f2232d875e36b8774c36ffd027dc1d606 Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@redhat.com>
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 <danielmicay@gmail.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Florian Weimer <fweimer@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
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 797295e792b2f..229d04a83f856 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)
--
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