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Date: Mon, 7 Jun 2021 11:15:37 +0200
From: Marco Elver <elver@...gle.com>
To: Andrey Konovalov <andreyknvl@...il.com>
Cc: David Gow <davidgow@...gle.com>,
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 Development <kunit-dev@...glegroups.com>,
LKML <linux-kernel@...r.kernel.org>,
Jonathan Corbet <corbet@....net>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3] kasan: test: Improve failure message in KUNIT_EXPECT_KASAN_FAIL()
On Sun, 6 Jun 2021 at 11:57, Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> 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>
Reviewed-by: Marco Elver <elver@...gle.com>
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