From:   Kees Cook <keescook@chromium.org>
To:     Marco Elver <elver@google.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: [PATCH] kasan: test: Silence intentional read overflow warnings
Date:   Mon, 15 Nov 2021 16:41:11 -0800
Message-Id: <20211116004111.3171781-1-keescook@chromium.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

As done in commit d73dad4eb5ad ("kasan: test: bypass __alloc_size checks")
for __write_overflow warnings, also silence some more cases that trip
the __read_overflow warnings seen in 5.16-rc1[1]:

In file included from /kisskb/src/include/linux/string.h:253,
                 from /kisskb/src/include/linux/bitmap.h:10,
                 from /kisskb/src/include/linux/cpumask.h:12,
                 from /kisskb/src/include/linux/mm_types_task.h:14,
                 from /kisskb/src/include/linux/mm_types.h:5,
                 from /kisskb/src/include/linux/page-flags.h:13,
                 from /kisskb/src/arch/arm64/include/asm/mte.h:14,
                 from /kisskb/src/arch/arm64/include/asm/pgtable.h:12,
                 from /kisskb/src/include/linux/pgtable.h:6,
                 from /kisskb/src/include/linux/kasan.h:29,
                 from /kisskb/src/lib/test_kasan.c:10:
In function 'memcmp',
    inlined from 'kasan_memcmp' at /kisskb/src/lib/test_kasan.c:897:2:
/kisskb/src/include/linux/fortify-string.h:263:25: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter)
  263 |                         __read_overflow();
      |                         ^~~~~~~~~~~~~~~~~
In function 'memchr',
    inlined from 'kasan_memchr' at /kisskb/src/lib/test_kasan.c:872:2:
/kisskb/src/include/linux/fortify-string.h:277:17: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter)
  277 |                 __read_overflow();
      |                 ^~~~~~~~~~~~~~~~~

[1] http://kisskb.ellerman.id.au/kisskb/buildresult/14660585/log/

Cc: Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: kasan-dev@googlegroups.com
Fixes: d73dad4eb5ad ("kasan: test: bypass __alloc_size checks")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 lib/test_kasan.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 67ed689a0b1b..0643573f8686 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -869,6 +869,7 @@ static void kasan_memchr(struct kunit *test)
 	ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	OPTIMIZER_HIDE_VAR(size);
 	KUNIT_EXPECT_KASAN_FAIL(test,
 		kasan_ptr_result = memchr(ptr, '1', size + 1));
 
@@ -894,6 +895,7 @@ static void kasan_memcmp(struct kunit *test)
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 	memset(arr, 0, sizeof(arr));
 
+	OPTIMIZER_HIDE_VAR(size);
 	KUNIT_EXPECT_KASAN_FAIL(test,
 		kasan_int_result = memcmp(ptr, arr, size+1));
 	kfree(ptr);
-- 
2.30.2