[PATCH 1/2] kasan: test: use underlying string helpers

[Arnd Bergmann <arnd@kernel.org>]

From: Arnd Bergmann <arnd@arndb.de>

Calling memcmp() and memchr() with an intentional buffer overflow
is now caught at compile time:

In function 'memcmp',
    inlined from 'kasan_memcmp' at lib/test_kasan.c:897:2:
include/linux/fortify-string.h:263:25: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter)
  263 |                         __read_overflow();
      |                         ^~~~~~~~~~~~~~~~~
In function 'memchr',
    inlined from 'kasan_memchr' at lib/test_kasan.c:872:2:
include/linux/fortify-string.h:277:17: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter)
  277 |                 __read_overflow();
      |                 ^~~~~~~~~~~~~~~~~

Change the kasan tests to wrap those inside of a noinline function
to prevent the compiler from noticing the bug and let kasan find
it at runtime.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 lib/test_kasan.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 67ed689a0b1b..903215e944f1 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -852,6 +852,21 @@ static void kmem_cache_invalid_free(struct kunit *test)
 	kmem_cache_destroy(cache);
 }
 
+/*
+ * noinline wrappers to prevent the compiler from noticing the overflow
+ * at compile time rather than having kasan catch it.
+ * */
+static noinline void *__kasan_memchr(const void *s, int c, size_t n)
+{
+	return memchr(s, c, n);
+}
+
+static noinline int __kasan_memcmp(const void *s1, const void *s2, size_t n)
+{
+	return memcmp(s1, s2, n);
+}
+
+
 static void kasan_memchr(struct kunit *test)
 {
 	char *ptr;
@@ -870,7 +885,7 @@ static void kasan_memchr(struct kunit *test)
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
 	KUNIT_EXPECT_KASAN_FAIL(test,
-		kasan_ptr_result = memchr(ptr, '1', size + 1));
+		kasan_ptr_result = __kasan_memchr(ptr, '1', size + 1));
 
 	kfree(ptr);
 }
@@ -895,7 +910,7 @@ static void kasan_memcmp(struct kunit *test)
 	memset(arr, 0, sizeof(arr));
 
 	KUNIT_EXPECT_KASAN_FAIL(test,
-		kasan_int_result = memcmp(ptr, arr, size+1));
+		kasan_int_result = __kasan_memcmp(ptr, arr, size+1));
 	kfree(ptr);
 }
 
-- 
2.29.2