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Date: Fri, 2 Jun 2017 11:20:10 -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 6/6] powerpc,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.
Inspired by Daniel Micay's linux-hardened tree.
Reported-by: Florian Weimer <fweimer@...hat.com>
Signed-off-by: Rik van Riel <riel@...hat.com>
---
arch/powerpc/mm/mmap.c | 28 +++++++++++++++++++---------
1 file changed, 19 insertions(+), 9 deletions(-)
diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
index 9dbd2a733d6b..354cfa22e5d4 100644
--- a/arch/powerpc/mm/mmap.c
+++ b/arch/powerpc/mm/mmap.c
@@ -34,16 +34,9 @@
/*
* Top of mmap area (just below the process stack).
*
- * Leave at least a ~128 MB hole on 32bit applications.
- *
- * On 64bit applications we randomise the stack by 1GB so we need to
- * space our mmap start address by a further 1GB, otherwise there is a
- * chance the mmap area will end up closer to the stack than our ulimit
- * requires.
+ * Leave at least a ~128 MB hole.
*/
-#define MIN_GAP32 (128*1024*1024)
-#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
-#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
+#define MIN_GAP (128*1024*1024)
#define MAX_GAP (TASK_SIZE/6*5)
static inline int mmap_is_legacy(void)
@@ -71,9 +64,26 @@ unsigned long arch_mmap_rnd(void)
return rnd << PAGE_SHIFT;
}
+static inline unsigned long stack_maxrandom_size(void)
+{
+ if (!(current->flags & PF_RANDOMIZE))
+ return 0;
+
+ /* 8MB for 32bit, 1GB for 64bit */
+ if (is_32bit_task())
+ return (1<<23);
+ else
+ return (1<<30);
+}
+
static inline unsigned long mmap_base(unsigned long rnd)
{
unsigned long gap = rlimit(RLIMIT_STACK);
+ unsigned long pad = stack_maxrandom_size();
+
+ /* 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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