Re: [PATCH v3 03/11] arm64: Consider stack randomization for mmap base only when necessary

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On 4/18/19 12:37 AM, Kees Cook wrote:
On Wed, Apr 17, 2019 at 12:26 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
Do not offset mmap base address because of stack randomization if
current task does not want randomization.
Maybe mention that this makes this logic match the existing x86 behavior too?


Ok I will add this in case of a v4.



Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks !



-Kees

---
  arch/arm64/mm/mmap.c | 6 +++++-
  1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index ed4f9915f2b8..ac89686c4af8 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -65,7 +65,11 @@ unsigned long arch_mmap_rnd(void)
  static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
  {
         unsigned long gap = rlim_stack->rlim_cur;
-       unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
+       unsigned long pad = stack_guard_gap;
+
+       /* Account for stack randomization if necessary */
+       if (current->flags & PF_RANDOMIZE)
+               pad += (STACK_RND_MASK << PAGE_SHIFT);

         /* Values close to RLIM_INFINITY can overflow. */
         if (gap + pad > gap)
--
2.20.1





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