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Date: Fri, 2 Jun 2017 11:20:08 -0400
From: riel@...hat.com
To: linux-kernel@...r.kernel.org
Cc: kernel-hardening@...ts.openwall.com, akpm@...ux-foundation.org,
mingo@...nel.org, oleg@...hat.com, lwoodman@...hat.com, mhocko@...e.de,
danielmicay@...il.com, will.deacon@....com, benh@...nel.crashing.org
Subject: [PATCH 4/6] arm64/mmap: properly account for stack randomization in mmap_base
From: Rik van Riel <riel@...hat.com>
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 into account.
>From Daniel Micay's linux-hardened tree.
Reported-by: Florian Weimer <fweimer@...hat.com>
Signed-off-by: Daniel Micay <danielmicay@...il.com>
Signed-off-by: Rik van Riel <riel@...hat.com>
---
arch/arm64/mm/mmap.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 7b0d55756eb1..3f15eb193e33 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -34,7 +34,7 @@
* 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)
@@ -64,6 +64,11 @@ 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;
+
+ /* Values close to RLIM_INFINITY can overflow. */
+ if (gap + pad > gap)
+ gap += pad;
if (gap < MIN_GAP)
gap = MIN_GAP;
--
2.9.3
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