Verify that KASAN does not quarantine objects in SLAB_TYPESAFE_BY_RCU slabs
if CONFIG_SLUB_RCU_DEBUG is off.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Jann Horn <jannh@google.com>
---
Changes in v3:
 - add vbabka's ack
 - make comment more verbose (andreyknvl)
 - Link to v2: https://lore.kernel.org/r/20250729-kasan-tsbrcu-noquarantine-test-v2-1-d16bd99309c9@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 | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index 5f922dd38ffa..0affadb201c2 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -1073,6 +1073,45 @@ 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.
+ * Without this, KASAN builds would be unable to trigger bugs caused by
+ * SLAB_TYPESAFE_BY_RCU users handling reycled objects improperly.
+ */
+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);
+
+	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 +2137,7 @@ 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>

On Thu, Aug 14, 2025 at 5:11 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.
>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
> Changes in v3:
>  - add vbabka's ack
>  - make comment more verbose (andreyknvl)
>  - Link to v2: https://lore.kernel.org/r/20250729-kasan-tsbrcu-noquarantine-test-v2-1-d16bd99309c9@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 | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
>
> diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> index 5f922dd38ffa..0affadb201c2 100644
> --- a/mm/kasan/kasan_test_c.c
> +++ b/mm/kasan/kasan_test_c.c
> @@ -1073,6 +1073,45 @@ 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.
> + * Without this, KASAN builds would be unable to trigger bugs caused by
> + * SLAB_TYPESAFE_BY_RCU users handling reycled objects improperly.
> + */
> +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);
> +
> +       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 +2137,7 @@ 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>
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>

Thank you!