[PATCH 2/3] arm64/mmap: properly account for stack randomization in mmap_base
Date: Thu Jun 22 2017 - 16:01:04 EST
From: Rik van Riel <riel@xxxxxxxxxx>
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.
>From Daniel Micay's linux-hardened tree.
Reported-by: Florian Weimer <fweimer@xxxxxxxxxx>
Signed-off-by: Daniel Micay <danielmicay@xxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
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..a0cb6b8ccde7 100644
@@ -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) + stack_guard_gap;
+ /* Values close to RLIM_INFINITY can overflow. */
+ if (gap + pad > gap)
+ gap += pad;
if (gap < MIN_GAP)
gap = MIN_GAP;