linux-kernel - [PATCH] kasan: test: Improve failure message in KUNIT_EXPECT_KASAN

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Date:   Thu,  3 Jun 2021 22:25:48 -0700
From:   David Gow <davidgow@...gle.com>
To:     Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Daniel Axtens <dja@...ens.net>,
        Brendan Higgins <brendanhiggins@...gle.com>
Cc:     David Gow <davidgow@...gle.com>, kasan-dev@...glegroups.com,
        kunit-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: [PATCH] kasan: test: Improve failure message in KUNIT_EXPECT_KASAN_FAIL()

The KUNIT_EXPECT_KASAN_FAIL() macro currently uses KUNIT_EXPECT_EQ() to
compare fail_data.report_expected and fail_data.report_found. This
always gave a somewhat useless error message on failure, but the
addition of extra compile-time checking with READ_ONCE() has caused it
to get much longer, and be truncated before anything useful is displayed.

Instead, just check fail_data.report_found by hand (we've just test
report_expected to 'true'), and print a better failure message with
KUNIT_FAIL()

Beforehand, a failure in:
KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)area)[3100]);
would looked like:
[22:00:34] [FAILED] vmalloc_oob
[22:00:34]     # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:991
[22:00:34]     Expected ({ do { extern void __compiletime_assert_705(void) __attribute__((__error__("Unsupported access size for {READ,WRITE}_ONCE()."))); if (!((sizeof(fail_data.report_expected) == sizeof(char) || sizeof(fail_data.repp
[22:00:34]     not ok 45 - vmalloc_oob

With this change, it instead looks like:
[22:04:04] [FAILED] vmalloc_oob
[22:04:04]     # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:993
[22:04:04]     KASAN failure expected in "((volatile char *)area)[3100]", but none occurred
[22:04:04]     not ok 45 - vmalloc_oob

Signed-off-by: David Gow <davidgow@...gle.com>
---

Stumbled across this because the vmalloc_oob test is failing (i.e.,
KASAN isn't picking up an error) under qemu on my system, and the
message above was horrifying. (I'll file a Bugzilla bug for the test
failure today.)

Cheers,
-- David

 lib/test_kasan.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index cacbbbdef768..deda13c9d9ff 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -98,9 +98,11 @@ static void kasan_test_exit(struct kunit *test)
 	barrier();							\
 	expression;							\
 	barrier();							\
-	KUNIT_EXPECT_EQ(test,						\
-			READ_ONCE(fail_data.report_expected),		\
-			READ_ONCE(fail_data.report_found));		\
+	if (READ_ONCE(fail_data.report_found) == false) {		\
+		KUNIT_FAIL(test, KUNIT_SUBTEST_INDENT "KASAN failure "	\
+				"expected in \"" #expression		\
+				 "\", but none occurred");		\
+	}								\
 	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) {				\
 		if (READ_ONCE(fail_data.report_found))			\
 			kasan_enable_tagging_sync();			\
-- 
2.32.0.rc1.229.g3e70b5a671-goog