[PATCH v4 01/10] arm: factor out mmap ASLR into mmap_rnd

Kees Cook
2015-03-04T21:14:45Z

In preparation for splitting out ET_DYN ASLR, this moves the ASLR calculations
for mmap on ARM into a separate routine, similar to x86. This also removes
the redundant check of personality (PF_RANDOMIZE is already set before calling
arch_pick_mmap_layout).

Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/arm/mm/mmap.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index 5e85ed371364..15a8160096b3 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -169,14 +169,22 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
return addr;
}

+static unsigned long mmap_rnd(void)
+{
+ unsigned long rnd;
+
+ /* 8 bits of randomness in 20 address space bits */
+ rnd = (unsigned long)get_random_int() % (1 << 8);
+
+ return rnd << PAGE_SHIFT;
+}
+
void arch_pick_mmap_layout(struct mm_struct *mm)
{
unsigned long random_factor = 0UL;

- /* 8 bits of randomness in 20 address space bits */
- if ((current->flags & PF_RANDOMIZE) &&
- !(current->personality & ADDR_NO_RANDOMIZE))
- random_factor = (get_random_int() % (1 << 8)) << PAGE_SHIFT;
+ if (current->flags & PF_RANDOMIZE)
+ random_factor = mmap_rnd();

if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
--
1.9.1