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Subject[PATCH 2/2] s390/mmap: randomize mmap base for bottom up direction
Date
Implement mmap base randomization for the bottom up direction, so ASLR works
for both mmap layouts on s390.
See also df54d6fa54 "x86 get_unmapped_area(): use proper mmap base for
bottom-up direction".

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
arch/s390/mm/mmap.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 4002329..7110c0f 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -64,6 +64,11 @@ static unsigned long mmap_rnd(void)
return (get_random_int() & 0x7ffUL) << PAGE_SHIFT;
}

+static unsigned long mmap_base_legacy(void)
+{
+ return TASK_UNMAPPED_BASE + mmap_rnd();
+}
+
static inline unsigned long mmap_base(void)
{
unsigned long gap = rlimit(RLIMIT_STACK);
@@ -89,7 +94,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
* bit is set, or if the expected stack growth is unlimited:
*/
if (mmap_is_legacy()) {
- mm->mmap_base = TASK_UNMAPPED_BASE;
+ mm->mmap_base = mmap_base_legacy();
mm->get_unmapped_area = arch_get_unmapped_area;
} else {
mm->mmap_base = mmap_base();
@@ -172,7 +177,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
* bit is set, or if the expected stack growth is unlimited:
*/
if (mmap_is_legacy()) {
- mm->mmap_base = TASK_UNMAPPED_BASE;
+ mm->mmap_base = mmap_base_legacy();
mm->get_unmapped_area = s390_get_unmapped_area;
} else {
mm->mmap_base = mmap_base();
--
1.8.3.4


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