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AKwUvByCjGNDSC4NW1EKfjUjyZgJzWoJQ0vZjtVen4HSDYoP748msA1mTTBiZ58VkH+ALLxVXhHNB2R56A==@kvack.org X-Gm-Message-State: AFuF++lyF2SYbIYhbq7KpqdUS2MDZKdQnG0lrbz8iZOtZJO3+KNN0Bp7 nfOk0C+jvzaSlTzM3KKSXRZyTUg/OEzSW9nV32fcQV5zuOSLW/P6S/IXUrqMZ+UOrlVP3roaOK5 3 X-Received: from pfra18.prod.google.com ([2002:aa7:8e92:0:b0:84a:2e0d:e14f]) (user=morbo job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:2e85:b0:881:fffd:26af with SMTP id d2e1a72fcca58-881fffd2c53mr4983469b3a.44.1790637460762; Mon, 28 Sep 2026 16:17:40 -0700 (PDT) Date: Mon, 28 Sep 2026 23:17:37 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Message-ID: <20260928231737.2092716-1-morbo@google.com> Subject: [PATCH] kasan: add KUnit tests for __counted_by and __counted_by_ptr From: Bill Wendling To: Andrey Ryabinin , Andrew Morton Cc: Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Kees Cook , "Gustavo A. R. Silva" , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, thomas.weissschuh@linutronix.de, Bill Wendling Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Stat-Signature: dt6tuzizwgrwytdsxw6zwnxzo3f48cuw X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 749FB1C0007 X-HE-Tag: 1790637462-460299 X-HE-Meta: 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 ue5p+1pX 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The '__counted_by' and '__counted_by_ptr' attributes associate a flexible array member or pointer member with a struct field that holds its element count. Supporting compilers use these annotations to compute dynamic object sizes via '__builtin_dynamic_object_size()' and perform runtime bounds checking with KASAN. Add KUnit tests ('counted_by_flex_oob_access' and 'counted_by_ptr_oob_access', guarded by CONFIG_CC_HAS_COUNTED_BY and CONFIG_CC_HAS_COUNTED_BY_PTR respectively) to verify that: - '__builtin_dynamic_object_size()' returns the expected byte size for annotated flexible array and pointer members. - KASAN detects out-of-bounds read and write accesses beyond the annotated count. Allocate the test structures in 'noinline' helpers and hide the returned pointers with OPTIMIZER_HIDE_VAR() so allocation-size attributes and compiler optimizations do not mask the '__counted_by' and '__counted_by_ptr' checks. Signed-off-by: Bill Wendling --- mm/kasan/kasan_test_c.c | 100 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 100 insertions(+) diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c index b9e167ed5be3..f481183c84f1 100644 --- a/mm/kasan/kasan_test_c.c +++ b/mm/kasan/kasan_test_c.c @@ -2201,6 +2201,100 @@ static void copy_user_test_oob(struct kunit *test) unused = strncpy_from_user(kmem, usermem, size + 1)); } +#ifdef CONFIG_CC_HAS_COUNTED_BY +struct counted_by_flex_struct { + size_t size; + int array[] __counted_by(size); +}; + +/* + * Allocate the struct out-of-line to prevent inherent attributes from + * affecting the '__builtin_dynamic_object_size' check. + */ +static noinline struct counted_by_flex_struct * +alloc_counted_by_flex_struct(struct kunit *test, size_t size) +{ + struct counted_by_flex_struct *s; + + s = kzalloc(sizeof(struct counted_by_flex_struct) + + size * sizeof(s->array[0]), GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, s); + + s->size = size; + return s; +} + +static void counted_by_flex_oob_access(struct kunit *test) +{ + size_t size = 128; + struct counted_by_flex_struct *s; + + s = alloc_counted_by_flex_struct(test, size); + + OPTIMIZER_HIDE_VAR(s); + + /* __builtin_dynamic_object_size() should return the correct length. */ + KUNIT_EXPECT_EQ(test, size * sizeof(s->array[0]), + __builtin_dynamic_object_size(s->array, 0)); + + /* Out-of-bounds assignment. */ + KUNIT_EXPECT_KASAN_FAIL(test, s->array[size + 1] = 42); + + /* Out-of-bounds read. */ + KUNIT_EXPECT_KASAN_FAIL_READ(test, s->array[0] = s->array[size + 13]); + + kfree(s); +} + +#ifdef CONFIG_CC_HAS_COUNTED_BY_PTR +struct counted_by_ptr_struct { + char *ptr __counted_by_ptr(size); + size_t size; +}; + +/* + * Allocate the struct out-of-line to prevent inherent attributes from + * affecting the '__builtin_dynamic_object_size' check. + */ +static noinline struct counted_by_ptr_struct * +alloc_counted_by_ptr_struct(struct kunit *test, size_t size) +{ + struct counted_by_ptr_struct *s; + + s = kmalloc_obj(struct counted_by_ptr_struct); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, s); + + s->size = size; + s->ptr = kzalloc(size, GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, s->ptr); + + return s; +} + +static void counted_by_ptr_oob_access(struct kunit *test) +{ + size_t size = 128; + struct counted_by_ptr_struct *s; + + s = alloc_counted_by_ptr_struct(test, size); + + OPTIMIZER_HIDE_VAR(s); + + /* __builtin_dynamic_object_size() should return the correct length. */ + KUNIT_EXPECT_EQ(test, size, __builtin_dynamic_object_size(s->ptr, 0)); + + /* Out-of-bounds assignment. */ + KUNIT_EXPECT_KASAN_FAIL(test, s->ptr[size + 1] = 42); + + /* Out-of-bounds read. */ + KUNIT_EXPECT_KASAN_FAIL_READ(test, s->ptr[0] = s->ptr[size + 13]); + + kfree(s->ptr); + kfree(s); +} +#endif /* CONFIG_CC_HAS_COUNTED_BY_PTR */ +#endif /* CONFIG_CC_HAS_COUNTED_BY */ + static struct kunit_case kasan_kunit_test_cases[] = { KUNIT_CASE(kmalloc_oob_right), KUNIT_CASE(kmalloc_oob_left), @@ -2280,6 +2374,12 @@ static struct kunit_case kasan_kunit_test_cases[] = { #endif KUNIT_CASE(rust_uaf), KUNIT_CASE(copy_user_test_oob), +#ifdef CONFIG_CC_HAS_COUNTED_BY + KUNIT_CASE(counted_by_flex_oob_access), +#ifdef CONFIG_CC_HAS_COUNTED_BY_PTR + KUNIT_CASE(counted_by_ptr_oob_access), +#endif /* CONFIG_CC_HAS_COUNTED_BY_PTR */ +#endif /* CONFIG_CC_HAS_COUNTED_BY */ {} }; -- 2.56.0.rc1.315.gc6ed9934b7-goog