Re: [PATCH 3/8] kasan: test: avoid corrupting memory via memset

[Andrey Konovalov <andreyknvl@gmail.com>]

On Thu, Aug 12, 2021 at 10:57 AM Marco Elver <elver@google.com> wrote:
>
> On Wed, 11 Aug 2021 at 21:21, <andrey.konovalov@linux.dev> wrote:
> > From: Andrey Konovalov <andreyknvl@gmail.com>
> >
> > kmalloc_oob_memset_*() tests do writes past the allocated objects.
> > As the result, they corrupt memory, which might lead to crashes with the
> > HW_TAGS mode, as it neither uses quarantine nor redzones.
> >
> > Adjust the tests to only write memory within the aligned kmalloc objects.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>
> > ---
> >  lib/test_kasan.c | 22 +++++++++++-----------
> >  1 file changed, 11 insertions(+), 11 deletions(-)
> >
> > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> > index c82a82eb5393..fd00cd35e82c 100644
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -431,61 +431,61 @@ static void kmalloc_uaf_16(struct kunit *test)
> >  static void kmalloc_oob_memset_2(struct kunit *test)
> >  {
> >         char *ptr;
> > -       size_t size = 8;
> > +       size_t size = 128 - KASAN_GRANULE_SIZE;
> >
> >         ptr = kmalloc(size, GFP_KERNEL);
> >         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + 7 + OOB_TAG_OFF, 0, 2));
> > +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size, 0, 2));
>
> I think one important aspect of these tests in generic mode is that
> the written range touches both valid and invalid memory. I think that
> was meant to test any explicit instrumentation isn't just looking at
> the starting address, but at the whole range.

Good point!

> It seems that with these changes that is no longer tested. Could we
> somehow make it still test that?

Yes, will do in v2.

Thanks, Marco!