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

[Andrey Konovalov <andreyknvl@gmail.com>]

On Wed, Nov 17, 2021 at 12:09 PM Marco Elver <elver@google.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@gmail.com>
> Signed-off-by: Marco Elver <elver@google.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.

> +       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@gmail.com>

Thanks!