On Wed, 13 Jan 2021 at 17:22, Andrey Konovalov <andreyknvl@xxxxxxxxxx> 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 <andreyknvl@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> > --- > 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 >
