[PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test

[Andrey Konovalov]

Since the hardware tag-based KASAN mode might not have a redzone that
comes after an allocated object (when kasan.mode=prod is enabled), the
kasan_bitops_tags() test ends up corrupting the next object in memory.

Change the test so it always accesses the redzone that lies within the
allocated object's boundaries.

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
Link: https://linux-review.googlesource.com/id/I67f51d1ee48f0a8d0fe2658c2a39e4879fe0832a
---
 lib/test_kasan.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index b67da7f6e17f..3ea52da52714 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -771,17 +771,17 @@ static void kasan_bitops_tags(struct kunit *test)
 
 	/* This test is specifically crafted for the tag-based mode. */
 	if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
-		kunit_info(test, "skipping, CONFIG_KASAN_SW_TAGS required");
+		kunit_info(test, "skipping, CONFIG_KASAN_SW/HW_TAGS required");
 		return;
 	}
 
-	/* Allocation size will be rounded to up granule size, which is 16. */
-	bits = kzalloc(sizeof(*bits), GFP_KERNEL);
+	/* kmalloc-64 cache will be used and the last 16 bytes will be the redzone. */
+	bits = kzalloc(48, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, bits);
 
-	/* Do the accesses past the 16 allocated bytes. */
-	kasan_bitops_modify(test, BITS_PER_LONG, &bits[1]);
-	kasan_bitops_test_and_modify(test, BITS_PER_LONG + BITS_PER_BYTE, &bits[1]);
+	/* Do the accesses past the 48 allocated bytes, but within the redone. */
+	kasan_bitops_modify(test, BITS_PER_LONG, (void *)bits + 48);
+	kasan_bitops_test_and_modify(test, BITS_PER_LONG + BITS_PER_BYTE, (void *)bits + 48);
 
 	kfree(bits);
 }
-- 
2.29.2.729.g45daf8777d-goog