On Tue, Jan 05, 2021 at 07:27PM +0100, Andrey Konovalov wrote: > 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; > + Why do we even need a limit? Why not retry until ptr1 != ptr2? > KUNIT_EXPECT_KASAN_FAIL(test, ptr1[40] = 'x'); > KUNIT_EXPECT_PTR_NE(test, ptr1, ptr2); > > -- > 2.29.2.729.g45daf8777d-goog >
