The patch titled
Subject: kasan: add compiler barriers to KUNIT_EXPECT_KASAN_FAIL
has been added to the -mm tree. Its filename is
kasan-add-compiler-barriers-to-kunit_expect_kasan_fail.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/kasan-add-compiler-barriers-to-kunit_expect_kasan_fail.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/kasan-add-compiler-barriers-to-kunit_expect_kasan_fail.patch
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------------------------------------------------------
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)) \
hw_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) */
_
Patches currently in -mm which might be from andreyknvl@xxxxxxxxxx are
kasan-fix-hw_tags-boot-parameters.patch
kasan-prefix-global-functions-with-kasan_.patch
kasan-clarify-hw_tags-impact-on-tbi.patch
kasan-clean-up-comments-in-tests.patch
kasan-add-macros-to-simplify-checking-test-constraints.patch
kasan-add-match-all-tag-tests.patch
kasan-arm64-allow-using-kunit-tests-with-hw_tags-mode.patch
kasan-rename-config_test_kasan_module.patch
kasan-add-compiler-barriers-to-kunit_expect_kasan_fail.patch
kasan-adapt-kmalloc_uaf2-test-to-hw_tags-mode.patch
kasan-fix-memory-corruption-in-kasan_bitops_tags-test.patch
kasan-move-_ret_ip_-to-inline-wrappers.patch
kasan-fix-bug-detection-via-ksize-for-hw_tags-mode.patch
kasan-add-proper-page-allocator-tests.patch
kasan-add-a-test-for-kmem_cache_alloc-free_bulk.patch
kasan-dont-run-tests-when-kasan-is-not-enabled.patch
