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From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Sun, 6 Jun 2021 02:25:13 +0300
Message-ID: <CA+fCnZdAmVoGjTEQBoKQF0x_NtUau0jydSnF8bYHwDGRNFddHw@mail.gmail.com>
Subject: Re: [PATCH v2] kasan: test: Improve failure message in KUNIT_EXPECT_KASAN_FAIL()
To:     David Gow <davidgow@google.com>
Cc:     Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Daniel Axtens <dja@axtens.net>,
        Brendan Higgins <brendanhiggins@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        kunit-dev@googlegroups.com, LKML <linux-kernel@vger.kernel.org>
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On Sat, Jun 5, 2021 at 6:48 AM 'David Gow' via kasan-dev
<kasan-dev@googlegroups.com> wrote:
>
> The KUNIT_EXPECT_KASAN_FAIL() macro currently uses KUNIT_EXPECT_EQ() to
> compare fail_data.report_expected and fail_data.report_found. This
> always gave a somewhat useless error message on failure, but the
> addition of extra compile-time checking with READ_ONCE() has caused it
> to get much longer, and be truncated before anything useful is displayed.
>
> Instead, just check fail_data.report_found by hand (we've just set
> report_expected to 'true'), and print a better failure message with
> KUNIT_FAIL(). Because of this, report_expected is no longer used
> anywhere, and can be removed.
>
> Beforehand, a failure in:
> KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)area)[3100]);
> would have looked like:
> [22:00:34] [FAILED] vmalloc_oob
> [22:00:34]     # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:991
> [22:00:34]     Expected ({ do { extern void __compiletime_assert_705(void) __attribute__((__error__("Unsupported access size for {READ,WRITE}_ONCE()."))); if (!((sizeof(fail_data.report_expected) == sizeof(char) || sizeof(fail_data.repp
> [22:00:34]     not ok 45 - vmalloc_oob
>
> With this change, it instead looks like:
> [22:04:04] [FAILED] vmalloc_oob
> [22:04:04]     # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:993
> [22:04:04]     KASAN failure expected in "((volatile char *)area)[3100]", but none occurred
> [22:04:04]     not ok 45 - vmalloc_oob
>
> Signed-off-by: David Gow <davidgow@google.com>

Hi David,

Please also update the failure message in Documentation/dev-tools/kasan.rst.

Thank you!

> ---
> Changes since v1:
> https://groups.google.com/g/kasan-dev/c/CbabdwoXGlE
> - Remove fail_data.report_expected now that it's unused.
> - Use '!' instead of '== false' in the comparison.
> - Minor typo fixes in the commit message.
>
> The test failure being used as an example is tracked in:
> https://bugzilla.kernel.org/show_bug.cgi?id=213335
>
> Cheers,
> -- David
>
>  include/linux/kasan.h |  1 -
>  lib/test_kasan.c      | 11 +++++------
>  2 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index b1678a61e6a7..18cd5ec2f469 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -17,7 +17,6 @@ struct task_struct;
>
>  /* kasan_data struct is used in KUnit tests for KASAN expected failures */
>  struct kunit_kasan_expectation {
> -       bool report_expected;
>         bool report_found;
>  };
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index cacbbbdef768..44e08f4d9c52 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -55,7 +55,6 @@ 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;
> @@ -94,20 +93,20 @@ static void kasan_test_exit(struct kunit *test)
>             !kasan_async_mode_enabled())                                \
>                 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 (!READ_ONCE(fail_data.report_found)) {                       \
> +               KUNIT_FAIL(test, KUNIT_SUBTEST_INDENT "KASAN failure "  \
> +                               "expected in \"" #expression            \
> +                                "\", but none occurred");              \
> +       }                                                               \
>         if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) {                         \
>                 if (READ_ONCE(fail_data.report_found))                  \
>                         kasan_enable_tagging_sync();                    \
>                 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 {                  \
> --
> 2.32.0.rc1.229.g3e70b5a671-goog
>
> --
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