On Wed, 30 Nov 2022 at 09:57, Feng Tang <feng.tang@xxxxxxxxx> wrote:
>
> When kfence is enabled, the buffer allocated from the test case
> could be from a kfence pool, and the operation could be also
> caught and reported by kfence first, causing the case to fail.
>
> With default kfence setting, this is very difficult to be triggered.
> By changing CONFIG_KFENCE_NUM_OBJECTS from 255 to 16383, and
> CONFIG_KFENCE_SAMPLE_INTERVAL from 100 to 5, the allocation from
> kfence did hit 7 times in different slub_kunit cases out of 900
> times of boot test.
>
> To avoid this, initially we tried is_kfence_address() to check this
> and repeated allocation till finding a non-kfence address. Vlastimil
> Babka suggested SLAB_SKIP_KFENCE flag could be used to achieve this,
> and better add a wrapper function for simplifying cache creation.
>
> Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
> ---
> Changelog:
>
> since v2:
> * Don't make SKIP_KFENCE an allowd flag for cache creation, and
> solve a bug of failed cache creation issue (Marco Elver)
> * Add a wrapper cache creation function to simplify code
> including SKIP_KFENCE handling (Vlastimil Babka)
>
> lib/slub_kunit.c | 35 +++++++++++++++++++++++++----------
> 1 file changed, 25 insertions(+), 10 deletions(-)
>
> diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c
> index 7a0564d7cb7a..5b0c8e7eb6dc 100644
> --- a/lib/slub_kunit.c
> +++ b/lib/slub_kunit.c
> @@ -9,10 +9,25 @@
> static struct kunit_resource resource;
> static int slab_errors;
>
> +/*
> + * Wrapper function for kmem_cache_create(), which reduces 2 parameters:
> + * 'align' and 'ctor', and sets SLAB_SKIP_KFENCE flag to avoid getting an
> + * object from kfence pool, where the operation could be caught by both
> + * our test and kfence sanity check.
> + */
> +static struct kmem_cache *test_kmem_cache_create(const char *name,
> + unsigned int size, slab_flags_t flags)
> +{
> + struct kmem_cache *s = kmem_cache_create(name, size, 0,
> + (flags | SLAB_NO_USER_FLAGS), NULL);
> + s->flags |= SLAB_SKIP_KFENCE;
> + return s;
> +}
> +
> static void test_clobber_zone(struct kunit *test)
> {
> - struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_alloc", 64, 0,
> - SLAB_RED_ZONE|SLAB_NO_USER_FLAGS, NULL);
> + struct kmem_cache *s = test_kmem_cache_create("TestSlub_RZ_alloc", 64,
> + SLAB_RED_ZONE);
> u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>
> kasan_disable_current();
> @@ -29,8 +44,8 @@ static void test_clobber_zone(struct kunit *test)
> #ifndef CONFIG_KASAN
> static void test_next_pointer(struct kunit *test)
> {
> - struct kmem_cache *s = kmem_cache_create("TestSlub_next_ptr_free", 64, 0,
> - SLAB_POISON|SLAB_NO_USER_FLAGS, NULL);
> + struct kmem_cache *s = test_kmem_cache_create("TestSlub_next_ptr_free",
> + 64, SLAB_POISON);
> u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> unsigned long tmp;
> unsigned long *ptr_addr;
> @@ -74,8 +89,8 @@ static void test_next_pointer(struct kunit *test)
>
> static void test_first_word(struct kunit *test)
> {
> - struct kmem_cache *s = kmem_cache_create("TestSlub_1th_word_free", 64, 0,
> - SLAB_POISON|SLAB_NO_USER_FLAGS, NULL);
> + struct kmem_cache *s = test_kmem_cache_create("TestSlub_1th_word_free",
> + 64, SLAB_POISON);
> u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>
> kmem_cache_free(s, p);
> @@ -89,8 +104,8 @@ static void test_first_word(struct kunit *test)
>
> static void test_clobber_50th_byte(struct kunit *test)
> {
> - struct kmem_cache *s = kmem_cache_create("TestSlub_50th_word_free", 64, 0,
> - SLAB_POISON|SLAB_NO_USER_FLAGS, NULL);
> + struct kmem_cache *s = test_kmem_cache_create("TestSlub_50th_word_free",
> + 64, SLAB_POISON);
> u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>
> kmem_cache_free(s, p);
> @@ -105,8 +120,8 @@ static void test_clobber_50th_byte(struct kunit *test)
>
> static void test_clobber_redzone_free(struct kunit *test)
> {
> - struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_free", 64, 0,
> - SLAB_RED_ZONE|SLAB_NO_USER_FLAGS, NULL);
> + struct kmem_cache *s = test_kmem_cache_create("TestSlub_RZ_free", 64,
> + SLAB_RED_ZONE);
> u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>
> kasan_disable_current();
> --
> 2.34.1
>
