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SubjectRe: [PATCH 1/2] kasan: test: use underlying string helpers
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On 10/13/21 5:00 PM, Arnd Bergmann wrote:
> 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>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

> ---
> 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);
> }
>
>

--
Regards,
Vincenzo

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