Re: [PATCH] kasan: fix more unit tests with CONFIG_UBSAN_LOCAL_BOUNDS enabled

[Marco Elver <elver@google.com>]

On Sat, 19 Feb 2022 at 02:26, Peter Collingbourne <pcc@google.com> wrote:
>
> This is a followup to commit f649dc0e0d7b ("kasan: fix unit tests
> with CONFIG_UBSAN_LOCAL_BOUNDS enabled") that fixes tests that fail
> as a result of __alloc_size annotations being added to the kernel
> allocator functions.
>
> Link: https://linux-review.googlesource.com/id/I4334cafc5db600fda5cebb851b2ee9fd09fb46cc
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> Cc: <stable@vger.kernel.org> # 5.16.x
> Fixes: c37495d6254c ("slab: add __alloc_size attributes for better bounds checking")
> ---
>  lib/test_kasan.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 26a5c9007653..3bf8801d0e66 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -177,7 +177,8 @@ static void kmalloc_node_oob_right(struct kunit *test)
>   */
>  static void kmalloc_pagealloc_oob_right(struct kunit *test)
>  {
> -       char *ptr;
> +       /* See comment in kasan_global_oob_right. */
> +       char *volatile ptr;
>         size_t size = KMALLOC_MAX_CACHE_SIZE + 10;

I think more recently we've been using OPTIMIZER_HIDE_VAR() to hide
things from the compiler. Does OPTIMIZER_HIDE_VAR(ptr) right before
the access also work in this case?

I leave it to you which you think is cleaner - I'm guessing that we
might want to avoid volatile if we can.

>         KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_SLUB);
> @@ -272,7 +273,8 @@ static void kmalloc_large_oob_right(struct kunit *test)
>  static void krealloc_more_oob_helper(struct kunit *test,
>                                         size_t size1, size_t size2)
>  {
> -       char *ptr1, *ptr2;
> +       /* See comment in kasan_global_oob_right. */
> +       char *ptr1, *volatile ptr2;
>         size_t middle;
>
>         KUNIT_ASSERT_LT(test, size1, size2);
> @@ -304,7 +306,8 @@ static void krealloc_more_oob_helper(struct kunit *test,
>  static void krealloc_less_oob_helper(struct kunit *test,
>                                         size_t size1, size_t size2)
>  {
> -       char *ptr1, *ptr2;
> +       /* See comment in kasan_global_oob_right. */
> +       char *ptr1, *volatile ptr2;
>         size_t middle;
>
>         KUNIT_ASSERT_LT(test, size2, size1);
> --
> 2.35.1.473.g83b2b277ed-goog
>