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@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 502709db41c0f0ae66b274885ffcf4607bd1d86c..603fd7937b9457513654d8309a7b87e4a89df201 100644 (file)
--- 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))          \
                        kasan_enable_tagging();                 \
                migrate_enable();                               \
        }                                                       \

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index e93d7973792e846a7106d7d04f2033a9db866ee4..234f35a84f19e04d6d38cbff39cb15d7a0cad0d9 100644 (file)
--- 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) */