On Tue, Jan 12, 2021 at 2:39 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > 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? Then the test will hang if it's failing. Let's do up to 16 attempts, it should be more than enough in practice. Thanks!
