[PATCH] kasan: detect false-positives in tests

From: Andrey Konovalov
Date: Wed Mar 31 2021 - 12:25:53 EST


Currently, KASAN-KUnit tests can check that a particular annotated part
of code causes a KASAN report. However, they do not check that no unwanted
reports happen between the annotated parts.

This patch implements these checks.

It is done by setting report_data.report_found to false in
kasan_test_init() and at the end of KUNIT_EXPECT_KASAN_FAIL() and then
checking that it remains false at the beginning of
KUNIT_EXPECT_KASAN_FAIL() and in kasan_test_exit().

kunit_add_named_resource() call is moved to kasan_test_init(), and the
value of fail_data.report_expected is kept as false in between
KUNIT_EXPECT_KASAN_FAIL() annotations for consistency.

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
lib/test_kasan.c | 49 +++++++++++++++++++++++++++---------------------
1 file changed, 28 insertions(+), 21 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index d77c45edc7cd..bf9225002a7e 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -54,6 +54,10 @@ 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;
}

@@ -61,6 +65,7 @@ static void kasan_test_exit(struct kunit *test)
{
kasan_set_tagging_report_once(true);
kasan_restore_multi_shot(multishot);
+ KUNIT_EXPECT_FALSE(test, fail_data.report_found);
}

/**
@@ -78,28 +83,30 @@ static void kasan_test_exit(struct kunit *test)
* 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.
+ *
+ * In between KUNIT_EXPECT_KASAN_FAIL checks, fail_data.report_found is kept as
+ * false. This allows detecting KASAN reports that happen outside of the checks
+ * by asserting !fail_data.report_found at the start of KUNIT_EXPECT_KASAN_FAIL
+ * and in kasan_test_exit.
*/
-#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do { \
- if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) \
- migrate_disable(); \
- 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, \
- READ_ONCE(fail_data.report_expected), \
- READ_ONCE(fail_data.report_found)); \
- if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) { \
- if (READ_ONCE(fail_data.report_found)) \
- kasan_enable_tagging(); \
- migrate_enable(); \
- } \
+#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do { \
+ if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) \
+ 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 (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) { \
+ if (READ_ONCE(fail_data.report_found)) \
+ kasan_enable_tagging(); \
+ 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 { \
--
2.31.0.291.g576ba9dcdaf-goog