Re: [PATCH v2] kasan: add test for SLAB_TYPESAFE_BY_RCU quarantine skipping

[Andrey Konovalov <andreyknvl@gmail.com>]

On Tue, Jul 29, 2025 at 6:49 PM Jann Horn <jannh@google.com> wrote:
>
> Verify that KASAN does not quarantine objects in SLAB_TYPESAFE_BY_RCU slabs
> if CONFIG_SLUB_RCU_DEBUG is off.
>
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
> changes in v2:
>  - disable migration to ensure that all SLUB operations use the same
>    percpu state (vbabka)
>  - use EXPECT instead of ASSERT for pointer equality check so that
>    expectation failure doesn't terminate the test with migration still
>    disabled
> ---
>  mm/kasan/kasan_test_c.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
>
> diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> index 5f922dd38ffa..0d50402d492c 100644
> --- a/mm/kasan/kasan_test_c.c
> +++ b/mm/kasan/kasan_test_c.c
> @@ -1073,6 +1073,43 @@ static void kmem_cache_rcu_uaf(struct kunit *test)
>         kmem_cache_destroy(cache);
>  }
>
> +/*
> + * Check that SLAB_TYPESAFE_BY_RCU objects are immediately reused when
> + * CONFIG_SLUB_RCU_DEBUG is off, and stay at the same address.

Would be great to also add an explanation of why we want to test for
this (or a reference to the related fix commit?).

> + */
> +static void kmem_cache_rcu_reuse(struct kunit *test)
> +{
> +       char *p, *p2;
> +       struct kmem_cache *cache;
> +
> +       KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_SLUB_RCU_DEBUG);
> +
> +       cache = kmem_cache_create("test_cache", 16, 0, SLAB_TYPESAFE_BY_RCU,
> +                                 NULL);
> +       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, cache);
> +
> +       migrate_disable();
> +       p = kmem_cache_alloc(cache, GFP_KERNEL);
> +       if (!p) {
> +               kunit_err(test, "Allocation failed: %s\n", __func__);
> +               goto out;
> +       }
> +
> +       kmem_cache_free(cache, p);
> +       p2 = kmem_cache_alloc(cache, GFP_KERNEL);
> +       if (!p2) {
> +               kunit_err(test, "Allocation failed: %s\n", __func__);
> +               goto out;
> +       }
> +       KUNIT_EXPECT_PTR_EQ(test, p, p2);

I think this might fail for the HW_TAGS mode? The location will be
reused, but the tag will be different.

We could mark this test as Generic mode only.

> +
> +       kmem_cache_free(cache, p2);
> +
> +out:
> +       migrate_enable();
> +       kmem_cache_destroy(cache);
> +}
> +
>  static void kmem_cache_double_destroy(struct kunit *test)
>  {
>         struct kmem_cache *cache;
> @@ -2098,6 +2135,7 @@ static struct kunit_case kasan_kunit_test_cases[] = {
>         KUNIT_CASE(kmem_cache_double_free),
>         KUNIT_CASE(kmem_cache_invalid_free),
>         KUNIT_CASE(kmem_cache_rcu_uaf),
> +       KUNIT_CASE(kmem_cache_rcu_reuse),
>         KUNIT_CASE(kmem_cache_double_destroy),
>         KUNIT_CASE(kmem_cache_accounted),
>         KUNIT_CASE(kmem_cache_bulk),
>
> ---
> base-commit: 0df7d6c9705b283d5b71ee0ae86ead05bd3a55a9
> change-id: 20250728-kasan-tsbrcu-noquarantine-test-5c723367e056
> prerequisite-change-id: 20250723-kasan-tsbrcu-noquarantine-e207bb990e24:v1
> prerequisite-patch-id: 4fab9d3a121bfcaacc32a40f606b7c04e0c6fdd0
>
> --
> Jann Horn <jannh@google.com>
>

Thank you!