diff options
Diffstat (limited to 'arch/powerpc/mm')
| -rw-r--r-- | arch/powerpc/mm/mmap.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c index f7376dbb653..75dc7faaf91 100644 --- a/arch/powerpc/mm/mmap.c +++ b/arch/powerpc/mm/mmap.c @@ -46,6 +46,14 @@ static inline int mmap_is_legacy(void) return sysctl_legacy_va_layout; } +/* + * Since get_random_int() returns the same value within a 1 jiffy window, + * we will almost always get the same randomisation for the stack and mmap + * region. This will mean the relative distance between stack and mmap will + * be the same. + * + * To avoid this we can shift the randomness by 1 bit. + */ static unsigned long mmap_rnd(void) { unsigned long rnd = 0; @@ -53,11 +61,11 @@ static unsigned long mmap_rnd(void) if (current->flags & PF_RANDOMIZE) { /* 8MB for 32bit, 1GB for 64bit */ if (is_32bit_task()) - rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT))); + rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT))); else - rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT))); + rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT))); } - return rnd << PAGE_SHIFT; + return (rnd << PAGE_SHIFT) * 2; } static inline unsigned long mmap_base(void) |