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Date: Sun, 6 Jun 2021 12:56:53 +0300
From: Andrey Konovalov <andreyknvl@...il.com>
To: David Gow <davidgow@...gle.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Daniel Axtens <dja@...ens.net>,
Brendan Higgins <brendanhiggins@...gle.com>,
kasan-dev <kasan-dev@...glegroups.com>,
kunit-dev@...glegroups.com, LKML <linux-kernel@...r.kernel.org>,
Jonathan Corbet <corbet@....net>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v3] kasan: test: Improve failure message in KUNIT_EXPECT_KASAN_FAIL()
On Sun, Jun 6, 2021 at 3:55 AM 'David Gow' via kasan-dev
<kasan-dev@...glegroups.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
>
> Also update the example failure in the documentation to reflect this.
>
> Signed-off-by: David Gow <davidgow@...gle.com>
> ---
>
> Changes since v2:
> https://lkml.org/lkml/2021/6/4/1264
> - Update the example error in the documentation
>
> 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
>
>
>
> Documentation/dev-tools/kasan.rst | 9 ++++-----
> include/linux/kasan.h | 1 -
> lib/test_kasan.c | 11 +++++------
> 3 files changed, 9 insertions(+), 12 deletions(-)
>
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index d3f335ffc751..83ec4a556c19 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -447,11 +447,10 @@ When a test fails due to a failed ``kmalloc``::
>
> When a test fails due to a missing KASAN report::
>
> - # kmalloc_double_kzfree: EXPECTATION FAILED at lib/test_kasan.c:629
> - Expected kasan_data->report_expected == kasan_data->report_found, but
> - kasan_data->report_expected == 1
> - kasan_data->report_found == 0
> - not ok 28 - kmalloc_double_kzfree
> + # kmalloc_double_kzfree: EXPECTATION FAILED at lib/test_kasan.c:974
> + KASAN failure expected in "kfree_sensitive(ptr)", but none occurred
> + not ok 44 - kmalloc_double_kzfree
> +
>
> At the end the cumulative status of all KASAN tests is printed. On success::
>
> 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
Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>
Thanks!
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