kasan: detect false-positives in tests

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.

Link: https://lkml.kernel.org/r/48079c52cc329fbc52f4386996598d58022fb872.1617207873.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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);
 }
 
 /**
@@ -78,33 +83,31 @@ 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) &&			\
-	    !kasan_async_mode_enabled())			\
-		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();						\
-	if (kasan_async_mode_enabled())				\
-		kasan_force_async_fault();			\
-	barrier();						\
-	KUNIT_EXPECT_EQ(test,					\
-			READ_ONCE(fail_data.report_expected),	\
-			READ_ONCE(fail_data.report_found));	\
-	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS) &&			\
-	    !kasan_async_mode_enabled()) {			\
-		if (READ_ONCE(fail_data.report_found))		\
-			kasan_enable_tagging_sync();		\
-		migrate_enable();				\
-	}							\
+#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do {			\
+	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS) &&				\
+	    !kasan_async_mode_enabled())				\
+		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_sync();			\
+		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 {			\