From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan: add compiler barriers to KUNIT_EXPECT_KASAN_FAIL 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 Link: https://lkml.kernel.org/r/6f11596f367d8ae8f71d800351e9a5d91eda19f6.1610733117.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Branislav Rankov <Branislav.Rankov@xxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx> Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx> Cc: Peter Collingbourne <pcc@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/test_kasan.c | 17 ++++++++++++----- mm/kasan/report.c | 2 +- 2 files changed, 13 insertions(+), 6 deletions(-) --- a/lib/test_kasan.c~kasan-add-compiler-barriers-to-kunit_expect_kasan_fail +++ a/lib/test_kasan.c @@ -68,23 +68,30 @@ static void kasan_test_exit(struct kunit * 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)) \ kasan_enable_tagging(); \ migrate_enable(); \ } \ --- a/mm/kasan/report.c~kasan-add-compiler-barriers-to-kunit_expect_kasan_fail +++ a/mm/kasan/report.c @@ -331,7 +331,7 @@ static void kasan_update_kunit_status(st } 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) */ _
