Re: [PATCH] kasan: detect false-positives in tests

[Marco Elver]

On Wed, 31 Mar 2021 at 18:25, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> Currently, KASAN-KUnit tests can check that a particular annotated part
> of code causes a KASAN report. However, they do not check that no unwanted
> reports happen between the annotated parts.
>
> This patch implements these checks.
>
> It is done by setting report_data.report_found to false in
> kasan_test_init() and at the end of KUNIT_EXPECT_KASAN_FAIL() and then
> checking that it remains false at the beginning of
> KUNIT_EXPECT_KASAN_FAIL() and in kasan_test_exit().
>
> kunit_add_named_resource() call is moved to kasan_test_init(), and the
> value of fail_data.report_expected is kept as false in between
> KUNIT_EXPECT_KASAN_FAIL() annotations for consistency.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

Thank you!

> ---
>  lib/test_kasan.c | 49 +++++++++++++++++++++++++++---------------------
>  1 file changed, 28 insertions(+), 21 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index d77c45edc7cd..bf9225002a7e 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -54,6 +54,10 @@ static int kasan_test_init(struct kunit *test)
>
>         multishot = kasan_save_enable_multi_shot();
>         kasan_set_tagging_report_once(false);
> +       fail_data.report_found = false;
> +       fail_data.report_expected = false;
> +       kunit_add_named_resource(test, NULL, NULL, &resource,
> +                                       "kasan_data", &fail_data);
>         return 0;
>  }
>
> @@ -61,6 +65,7 @@ static void kasan_test_exit(struct kunit *test)
>  {
>         kasan_set_tagging_report_once(true);
>         kasan_restore_multi_shot(multishot);
> +       KUNIT_EXPECT_FALSE(test, fail_data.report_found);
>  }
>
>  /**
> @@ -78,28 +83,30 @@ static void kasan_test_exit(struct kunit *test)
>   * fields, it can reorder or optimize away the accesses to those fields.
>   * Use READ/WRITE_ONCE() for the accesses and compiler barriers around the
>   * expression to prevent that.
> + *
> + * In between KUNIT_EXPECT_KASAN_FAIL checks, fail_data.report_found is kept as
> + * false. This allows detecting KASAN reports that happen outside of the checks
> + * by asserting !fail_data.report_found at the start of KUNIT_EXPECT_KASAN_FAIL
> + * and in kasan_test_exit.
>   */
> -#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do {         \
> -       if (IS_ENABLED(CONFIG_KASAN_HW_TAGS))                   \
> -               migrate_disable();                              \
> -       WRITE_ONCE(fail_data.report_expected, true);            \
> -       WRITE_ONCE(fail_data.report_found, false);              \
> -       kunit_add_named_resource(test,                          \
> -                               NULL,                           \
> -                               NULL,                           \
> -                               &resource,                      \
> -                               "kasan_data", &fail_data);      \
> -       barrier();                                              \
> -       expression;                                             \
> -       barrier();                                              \
> -       KUNIT_EXPECT_EQ(test,                                   \
> -                       READ_ONCE(fail_data.report_expected),   \
> -                       READ_ONCE(fail_data.report_found));     \
> -       if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) {                 \
> -               if (READ_ONCE(fail_data.report_found))          \
> -                       kasan_enable_tagging();                 \
> -               migrate_enable();                               \
> -       }                                                       \
> +#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do {                 \
> +       if (IS_ENABLED(CONFIG_KASAN_HW_TAGS))                           \
> +               migrate_disable();                                      \
> +       KUNIT_EXPECT_FALSE(test, READ_ONCE(fail_data.report_found));    \
> +       WRITE_ONCE(fail_data.report_expected, true);                    \
> +       barrier();                                                      \
> +       expression;                                                     \
> +       barrier();                                                      \
> +       KUNIT_EXPECT_EQ(test,                                           \
> +                       READ_ONCE(fail_data.report_expected),           \
> +                       READ_ONCE(fail_data.report_found));             \
> +       if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) {                         \
> +               if (READ_ONCE(fail_data.report_found))                  \
> +                       kasan_enable_tagging();                         \
> +               migrate_enable();                                       \
> +       }                                                               \
> +       WRITE_ONCE(fail_data.report_found, false);                      \
> +       WRITE_ONCE(fail_data.report_expected, false);                   \
>  } while (0)
>
>  #define KASAN_TEST_NEEDS_CONFIG_ON(test, config) do {                  \
> --
> 2.31.0.291.g576ba9dcdaf-goog
>