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

[Vlastimil Babka <vbabka@suse.cz>]

On 7/28/25 17:25, Jann Horn wrote:
> Verify that KASAN does not quarantine objects in SLAB_TYPESAFE_BY_RCU slabs
> if CONFIG_SLUB_RCU_DEBUG is off.
> 
> Suggested-by: Andrey Konovalov <andreyknvl@gmail.com>
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
> Feel free to either take this as a separate commit or squash it into the
> preceding "[PATCH] kasan: skip quarantine if object is still accessible
> under RCU".
> 
> I tested this by running KASAN kunit tests for x86-64 with KASAN
> and tracing manually enabled; there are two failing tests but those
> seem unrelated (kasan_memchr is unexpectedly not detecting some
> accesses, and kasan_strings is also failing).
> ---
>  mm/kasan/kasan_test_c.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> index 5f922dd38ffa..15d3d82041bf 100644
> --- a/mm/kasan/kasan_test_c.c
> +++ b/mm/kasan/kasan_test_c.c
> @@ -1073,6 +1073,41 @@ 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.
> + */
> +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);

Hmm is there anything inherent in kunit that keeps the test pinned to the
same cpu? Otherwise I think you'll need here

migrate_disable();


> +	p = kmem_cache_alloc(cache, GFP_KERNEL);
> +	if (!p) {
> +		kunit_err(test, "Allocation failed: %s\n", __func__);
> +		kmem_cache_destroy(cache);
> +		return;
> +	}
> +
> +	kmem_cache_free(cache, p);
> +	p2 = kmem_cache_alloc(cache, GFP_KERNEL);

and here (or later)

migrate_enable();

> +	if (!p2) {
> +		kunit_err(test, "Allocation failed: %s\n", __func__);
> +		kmem_cache_destroy(cache);
> +		return;
> +	}
> +	KUNIT_ASSERT_PTR_EQ(test, p, p2);

Otherwise the cpu slab caching of SLUB and a migration could mean this won't
hold as you'll get object from another slab.

> +	kmem_cache_free(cache, p2);
> +	kmem_cache_destroy(cache);
> +}
> +
>  static void kmem_cache_double_destroy(struct kunit *test)
>  {
>  	struct kmem_cache *cache;
> @@ -2098,6 +2133,7 @@ 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
>