[PATCH 08/11] kasan: adopt kmalloc_uaf2 test to HW_TAGS mode

[Andrey Konovalov]

In the kmalloc_uaf2() test, the pointers to the two allocated memory
blocks might be the same, and the test will fail. With the software
tag-based mode, the probability of the that happening 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 4 attempts at generating different tags for the tag-based
modes.

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Link: https://linux-review.googlesource.com/id/Ibfa458ef2804ff465d8eb07434a300bf36388d55
---
 lib/test_kasan.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index b5077a47b95a..b67da7f6e17f 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -375,7 +375,9 @@ 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);
 
@@ -384,6 +386,13 @@ 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 4 attempts at generating different tags.
+	 */
+	if (!IS_ENABLED(CONFIG_KASAN_GENERIC) && ptr1 == ptr2 && counter++ < 4)
+		goto again;
+
 	KUNIT_EXPECT_KASAN_FAIL(test, ptr1[40] = 'x');
 	KUNIT_EXPECT_PTR_NE(test, ptr1, ptr2);
 
-- 
2.29.2.729.g45daf8777d-goog