[S390] Randomize mmap start address

Randomize mmap start address with 8MB.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 74d663f367e2..c9a9f7f18188 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -27,6 +27,7 @@
 #include <linux/personality.h>
 #include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/random.h>
 #include <asm/pgalloc.h>
 #include <asm/compat.h>
 
@@ -56,6 +57,14 @@ static inline int mmap_is_legacy(void)
         return sysctl_legacy_va_layout;
 }
 
+static unsigned long mmap_rnd(void)
+{
+        if (!(current->flags & PF_RANDOMIZE))
+                return 0;
+        /* 8MB randomization for mmap_base */
+        return (get_random_int() & 0x7ffUL) << PAGE_SHIFT;
+}
+
 static inline unsigned long mmap_base(void)
 {
         unsigned long gap = rlimit(RLIMIT_STACK);
@@ -64,8 +73,8 @@ static inline unsigned long mmap_base(void)
                 gap = MIN_GAP;
         else if (gap > MAX_GAP)
                 gap = MAX_GAP;
-
-        return STACK_TOP - stack_maxrandom_size() - (gap & PAGE_MASK);
+        gap &= PAGE_MASK;
+        return STACK_TOP - stack_maxrandom_size() - mmap_rnd() - gap;
 }
 
 #ifndef CONFIG_64BIT