Re: [PATCH v2 09/14] kasan: adapt kmalloc_uaf2 test to HW_TAGS mode
From: Marco Elver <elver@google.com>
Date: 2021-01-13 16:32:32
Also in:
linux-arm-kernel, lkml
On Wed, 13 Jan 2021 at 17:22, Andrey Konovalov [off-list ref] wrote:
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 Signed-off-by: Andrey Konovalov <redacted>
Reviewed-by: Marco Elver <elver@google.com>
quoted hunk ↗ jump to hunk
--- lib/test_kasan.c | 11 +++++++++++ 1 file changed, 11 insertions(+)diff --git a/lib/test_kasan.c b/lib/test_kasan.c index 283feda9882a..a1a35d75ee1e 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); --2.30.0.284.gd98b1dd5eaa7-goog