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Message-ID: <CANpmjNPYKzY+xPAddAjsry1RC2Y84pSCFZ0VuVMMEu+LN3A0EQ@mail.gmail.com>
Date: Wed, 13 Jan 2021 17:28:40 +0100
From: Marco Elver <elver@...gle.com>
To: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Will Deacon <will.deacon@....com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Peter Collingbourne <pcc@...gle.com>,
Evgenii Stepanov <eugenis@...gle.com>,
Branislav Rankov <Branislav.Rankov@....com>,
Kevin Brodsky <kevin.brodsky@....com>,
kasan-dev <kasan-dev@...glegroups.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux Memory Management List <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 08/14] kasan: add compiler barriers to KUNIT_EXPECT_KASAN_FAIL
On Wed, 13 Jan 2021 at 17:22, Andrey Konovalov <andreyknvl@...gle.com> wrote:
>
> It might not be obvious to the compiler that the expression must be
> executed between writing and reading to fail_data. In this case, the
> compiler might reorder or optimize away some of the accesses, and
> the tests will fail.
>
> Add compiler barriers around the expression in KUNIT_EXPECT_KASAN_FAIL
> and use READ/WRITE_ONCE() for accessing fail_data fields.
>
> Link: https://linux-review.googlesource.com/id/I046079f48641a1d36fe627fc8827a9249102fd50
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
Reviewed-by: Marco Elver <elver@...gle.com>
> ---
> lib/test_kasan.c | 17 ++++++++++++-----
> mm/kasan/report.c | 2 +-
> 2 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 5c8aa3a5ce93..283feda9882a 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -68,23 +68,30 @@ static void kasan_test_exit(struct kunit *test)
> * normally auto-disabled. When this happens, this test handler reenables
> * tag checking. As tag checking can be only disabled or enabled per CPU, this
> * handler disables migration (preemption).
> + *
> + * Since the compiler doesn't see that the expression can change the fail_data
> + * 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.
> */
> #define KUNIT_EXPECT_KASAN_FAIL(test, expression) do { \
> if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) \
> migrate_disable(); \
> - fail_data.report_expected = true; \
> - fail_data.report_found = false; \
> + 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, \
> - fail_data.report_expected, \
> - fail_data.report_found); \
> + READ_ONCE(fail_data.report_expected), \
> + READ_ONCE(fail_data.report_found)); \
> if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) { \
> - if (fail_data.report_found) \
> + if (READ_ONCE(fail_data.report_found)) \
> hw_enable_tagging(); \
> migrate_enable(); \
> } \
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index e93d7973792e..234f35a84f19 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -331,7 +331,7 @@ static void kasan_update_kunit_status(struct kunit *cur_test)
> }
>
> kasan_data = (struct kunit_kasan_expectation *)resource->data;
> - kasan_data->report_found = true;
> + WRITE_ONCE(kasan_data->report_found, true);
> kunit_put_resource(resource);
> }
> #endif /* IS_ENABLED(CONFIG_KUNIT) */
> --
> 2.30.0.284.gd98b1dd5eaa7-goog
>
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