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

On Tue, Jan 12, 2021 at 9:07 PM 'Andrey Konovalov' via kasan-dev
[off-list ref] wrote:

On Tue, Jan 12, 2021 at 9:30 AM Alexander Potapenko [off-list ref] wrote:

quoted

On Tue, Jan 5, 2021 at 7:28 PM Andrey Konovalov [off-list ref] wrote:

quoted

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 <redacted>
Link: https://linux-review.googlesource.com/id/I67f51d1ee48f0a8d0fe2658c2a39e4879fe0832a

Reviewed-by: Alexander Potapenko <glider@google.com>

quoted

quoted

---
 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);

I think it might make sense to call ksize() here to ensure we have
these spare bytes.

Calling ksize() will unpoison the whole object.

Ah, that's right.

I think it's OK to make assumptions about KASAN internals in tests. I
would actually say that we need more tests that check such internal
properties.

Agreed.