kasan: support use-after-scope detection

Gcc revision 241896 implements use-after-scope detection.  Will be
available in gcc 7.  Support it in KASAN.

Gcc emits 2 new callbacks to poison/unpoison large stack objects when
they go in/out of scope.  Implement the callbacks and add a test.

[dvyukov@google.com: v3]
  Link: http://lkml.kernel.org/r/1479998292-144502-1-git-send-email-dvyukov@google.com
Link: http://lkml.kernel.org/r/1479226045-145148-1-git-send-email-dvyukov@google.com
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: <stable@vger.kernel.org>	[4.0+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 5e51872b3fc1..fbdf87920093 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -20,6 +20,11 @@
 #include <linux/uaccess.h>
 #include <linux/module.h>
 
+/*
+ * Note: test functions are marked noinline so that their names appear in
+ * reports.
+ */
+
 static noinline void __init kmalloc_oob_right(void)
 {
         char *ptr;
@@ -411,6 +416,29 @@ static noinline void __init copy_user_test(void)
         kfree(kmem);
 }
 
+static noinline void __init use_after_scope_test(void)
+{
+        volatile char *volatile p;
+
+        pr_info("use-after-scope on int\n");
+        {
+                int local = 0;
+
+                p = (char *)&local;
+        }
+        p[0] = 1;
+        p[3] = 1;
+
+        pr_info("use-after-scope on array\n");
+        {
+                char local[1024] = {0};
+
+                p = local;
+        }
+        p[0] = 1;
+        p[1023] = 1;
+}
+
 static int __init kmalloc_tests_init(void)
 {
         kmalloc_oob_right();
@@ -436,6 +464,7 @@ static int __init kmalloc_tests_init(void)
         kasan_global_oob();
         ksize_unpoisons_memory();
         copy_user_test();
+        use_after_scope_test();
         return -EAGAIN;
 }