diff options
| author |   Anton Blanchard <anton@samba.org> | 2009-02-22 01:50:05 +0000 |
|---|---|---|
| committer |   Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2009-02-23 15:53:21 +1100 |
| commit | a5adc91a4b44b5d1706b9d906cc14fe4f312afe9 (patch) | |
| tree | f0f5053b44b53fea4065bd05aeb9f0a53090d9dd /arch/powerpc/mm/mmap.c | |
| parent | powerpc: Randomise the brk region (diff) | |
| download | linux-dev-a5adc91a4b44b5d1706b9d906cc14fe4f312afe9.tar.xz linux-dev-a5adc91a4b44b5d1706b9d906cc14fe4f312afe9.zip | |
powerpc: Ensure random space between stack and mmaps
get_random_int() returns the same value within a 1 jiffy interval. This means
that the mmap and stack regions will almost always end up the same distance
apart, making a relative offset based attack possible.
To fix this, shift the randomness we use for the mmap region by 1 bit.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/mm/mmap.c')
| -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 f7376dbb653b..75dc7faaf917 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) |