[v4,09/15] kasan: adapt kmalloc_uaf2 test to HW_TAGS mode
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Message ID 9cd5cf2f633dcbf55cab801cd26845d2b075cec7.1610733117.git.andreyknvl@google.com
State In Next
Commit c194ddf4304f4635ae8c7c495ec956423ff99143
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Series
  • kasan: HW_TAGS tests support and fixes
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Commit Message

Andrey Konovalov Jan. 15, 2021, 5:52 p.m. UTC
In the kmalloc_uaf2() test, the pointers to the two allocated memory
blocks might happen to be the same, and the test will fail. With the
software tag-based mode, the probability of the that is 1/254, so it's
hard to observe the failure. For the hardware tag-based mode though,
the probablity is 1/14, which is quite noticable.

Allow up to 16 attempts at generating different tags for the tag-based
modes.

Link: https://linux-review.googlesource.com/id/Ibfa458ef2804ff465d8eb07434a300bf36388d55
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/test_kasan.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

Patch
diff mbox series

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 2419e36e117b..0cda4a1ff394 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -382,7 +382,9 @@  static void kmalloc_uaf2(struct kunit *test)
 {
 	char *ptr1, *ptr2;
 	size_t size = 43;
+	int counter = 0;
 
+again:
 	ptr1 = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1);
 
@@ -391,6 +393,15 @@  static void kmalloc_uaf2(struct kunit *test)
 	ptr2 = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
 
+	/*
+	 * For tag-based KASAN ptr1 and ptr2 tags might happen to be the same.
+	 * Allow up to 16 attempts at generating different tags.
+	 */
+	if (!IS_ENABLED(CONFIG_KASAN_GENERIC) && ptr1 == ptr2 && counter++ < 16) {
+		kfree(ptr2);
+		goto again;
+	}
+
 	KUNIT_EXPECT_KASAN_FAIL(test, ptr1[40] = 'x');
 	KUNIT_EXPECT_PTR_NE(test, ptr1, ptr2);