[PATCH v4 03/14] arm64: Consider stack randomization for mmap base only when necessary

[Alexandre Ghiti]

Do not offset mmap base address because of stack randomization if
current task does not want randomization.
Note that x86 already implements this behaviour.

Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
 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