linux-kernel - Re: [PATCH] kasan: test: add globals left-out-of-bounds test

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Date:   Wed, 17 Nov 2021 14:04:17 +0100
From:   Marco Elver <elver@...gle.com>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
Subject: Re: [PATCH] kasan: test: add globals left-out-of-bounds test

On Wed, 17 Nov 2021 at 13:59, Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> On Wed, Nov 17, 2021 at 12:09 PM Marco Elver <elver@...gle.com> wrote:
> >
> > Add a test checking that KASAN generic can also detect out-of-bounds
> > accesses to the left of globals.
> >
> > Unfortunately it seems that GCC doesn't catch this (tested GCC 10, 11).
> > The main difference between GCC's globals redzoning and Clang's is that
> > GCC relies on using increased alignment to producing padding, where
> > Clang's redzoning implementation actually adds real data after the
> > global and doesn't rely on alignment to produce padding. I believe this
> > is the main reason why GCC can't reliably catch globals out-of-bounds in
> > this case.
> >
> > Given this is now a known issue, to avoid failing the whole test suite,
> > skip this test case with GCC.
> >
> > Reported-by: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
> > Signed-off-by: Marco Elver <elver@...gle.com>
>
> Hi Marco,
>
> > ---
> >  lib/test_kasan.c | 18 ++++++++++++++++--
> >  1 file changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> > index 67ed689a0b1b..69c32c91420b 100644
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -700,7 +700,7 @@ static void kmem_cache_bulk(struct kunit *test)
> >
> >  static char global_array[10];
> >
> > -static void kasan_global_oob(struct kunit *test)
> > +static void kasan_global_oob_right(struct kunit *test)
> >  {
> >         /*
> >          * Deliberate out-of-bounds access. To prevent CONFIG_UBSAN_LOCAL_BOUNDS
> > @@ -723,6 +723,19 @@ static void kasan_global_oob(struct kunit *test)
> >         KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
> >  }
> >
> > +static void kasan_global_oob_left(struct kunit *test)
> > +{
> > +       char *volatile array = global_array;
> > +       char *p = array - 3;
> > +
> > +       /*
> > +        * GCC is known to fail this test, skip it.
> > +        */
>
> Please link the KASAN bugzilla issue here.

I was wondering how to solve the cyclic dependency, because I wanted
to link this patch from the bugzilla.

Now that the bugzilla entry exists, I guess I can add it and then
update bugzilla with link to this patch closing the cycle. :-)

> > +       KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_CC_IS_CLANG);
> > +       KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
> > +       KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
> > +}
> > +
> >  /* Check that ksize() makes the whole object accessible. */
> >  static void ksize_unpoisons_memory(struct kunit *test)
> >  {
> > @@ -1160,7 +1173,8 @@ static struct kunit_case kasan_kunit_test_cases[] = {
> >         KUNIT_CASE(kmem_cache_oob),
> >         KUNIT_CASE(kmem_cache_accounted),
> >         KUNIT_CASE(kmem_cache_bulk),
> > -       KUNIT_CASE(kasan_global_oob),
> > +       KUNIT_CASE(kasan_global_oob_right),
> > +       KUNIT_CASE(kasan_global_oob_left),
> >         KUNIT_CASE(kasan_stack_oob),
> >         KUNIT_CASE(kasan_alloca_oob_left),
> >         KUNIT_CASE(kasan_alloca_oob_right),
> > --
> > 2.34.0.rc2.393.gf8c9666880-goog
> >
>
> Otherwise:
>
> Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>
>
> Thanks!
>
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