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[PATCH] kasan: add test for SLAB_TYPESAFE_BY_RCU quarantine skipping

Jann Horn posted 1 patch 2 months, 1 week ago
There is a newer version of this series
mm/kasan/kasan_test_c.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
[PATCH] kasan: add test for SLAB_TYPESAFE_BY_RCU quarantine skipping
Posted by Jann Horn 2 months, 1 week ago 
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);
+
+	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);
+	if (!p2) {
+		kunit_err(test, "Allocation failed: %s\n", __func__);
+		kmem_cache_destroy(cache);
+		return;
+	}
+	KUNIT_ASSERT_PTR_EQ(test, p, p2);
+
+	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

-- 
Jann Horn <jannh@google.com>
Re: [PATCH] kasan: add test for SLAB_TYPESAFE_BY_RCU quarantine skipping
Posted by Vlastimil Babka 2 months, 1 week ago 
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
>
Re: [PATCH] kasan: add test for SLAB_TYPESAFE_BY_RCU quarantine skipping
Posted by Jann Horn 2 months, 1 week ago 
On Tue, Jul 29, 2025 at 6:14 PM Vlastimil Babka <vbabka@suse.cz> wrote:
> 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();

Oops, right, good point.

> > +     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.

Yeah...

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