Re: [PATCH] kasan: test: Improve failure message in KUNIT_EXPECT_KASAN_FAIL()

[Marco Elver]

On Fri, 4 Jun 2021 at 07:26, 'David Gow' via kasan-dev
<kasan-dev@xxxxxxxxxxxxxxxx> 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 test
> report_expected to 'true'), and print a better failure message with
> KUNIT_FAIL()
>
> Beforehand, a failure in:
> KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)area)[3100]);
> would 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@xxxxxxxxxx>
> ---
>
> Stumbled across this because the vmalloc_oob test is failing (i.e.,
> KASAN isn't picking up an error) under qemu on my system, and the
> message above was horrifying. (I'll file a Bugzilla bug for the test
> failure today.)
>
> Cheers,
> -- David
>
>  lib/test_kasan.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index cacbbbdef768..deda13c9d9ff 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -98,9 +98,11 @@ static void kasan_test_exit(struct kunit *test)
>         barrier();                                                      \
>         expression;                                                     \
>         barrier();                                                      \
> -       KUNIT_EXPECT_EQ(test,                                           \
> -                       READ_ONCE(fail_data.report_expected),           \

What do we have fail_data.report_expected for? Could we remove it now?
I think it's unused now.

> -                       READ_ONCE(fail_data.report_found));             \
> +       if (READ_ONCE(fail_data.report_found) == false) {               \

if (!READ_ONCE(fail_data.report_found)) {
?

> +               KUNIT_FAIL(test, KUNIT_SUBTEST_INDENT "KASAN failure "  \
> +                               "expected in \"" #expression            \
> +                                "\", but none occurred");              \
> +       }                                                               \

Thanks,
-- Marco