From: Kees Cook <keescook@chromium.org>
To: Arnd Bergmann <arnd@kernel.org>
Cc: linux-hardening@vger.kernel.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, Arnd Bergmann <arnd@arndb.de>,
Andrew Morton <akpm@linux-foundation.org>,
Marco Elver <elver@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Peter Collingbourne <pcc@google.com>,
Patricia Alfonso <trishalfonso@google.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] kasan: test: use underlying string helpers
Date: Mon, 18 Oct 2021 12:47:05 -0700 [thread overview]
Message-ID: <202110181245.499CB7594B@keescook> (raw)
In-Reply-To: <20211013150025.2875883-1-arnd@kernel.org>
On Wed, Oct 13, 2021 at 05:00:05PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> Calling memcmp() and memchr() with an intentional buffer overflow
> is now caught at compile time:
>
> In function 'memcmp',
> inlined from 'kasan_memcmp' at lib/test_kasan.c:897:2:
> 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 lib/test_kasan.c:872:2:
> 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();
> | ^~~~~~~~~~~~~~~~~
>
> Change the kasan tests to wrap those inside of a noinline function
> to prevent the compiler from noticing the bug and let kasan find
> it at runtime.
Is this with W=1 ? I had explicitly disabled the read overflows for
"phase 1" of the overflow restriction tightening...
(And what do you think of using OPTIMIZER_HIDE_VAR() instead[1]?
-Kees
[1] https://lore.kernel.org/linux-hardening/20211006181544.1670992-1-keescook@chromium.org/T/#u
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> lib/test_kasan.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 67ed689a0b1b..903215e944f1 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -852,6 +852,21 @@ static void kmem_cache_invalid_free(struct kunit *test)
> kmem_cache_destroy(cache);
> }
>
> +/*
> + * noinline wrappers to prevent the compiler from noticing the overflow
> + * at compile time rather than having kasan catch it.
> + * */
> +static noinline void *__kasan_memchr(const void *s, int c, size_t n)
> +{
> + return memchr(s, c, n);
> +}
> +
> +static noinline int __kasan_memcmp(const void *s1, const void *s2, size_t n)
> +{
> + return memcmp(s1, s2, n);
> +}
> +
> +
> static void kasan_memchr(struct kunit *test)
> {
> char *ptr;
> @@ -870,7 +885,7 @@ static void kasan_memchr(struct kunit *test)
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> KUNIT_EXPECT_KASAN_FAIL(test,
> - kasan_ptr_result = memchr(ptr, '1', size + 1));
> + kasan_ptr_result = __kasan_memchr(ptr, '1', size + 1));
>
> kfree(ptr);
> }
> @@ -895,7 +910,7 @@ static void kasan_memcmp(struct kunit *test)
> memset(arr, 0, sizeof(arr));
>
> KUNIT_EXPECT_KASAN_FAIL(test,
> - kasan_int_result = memcmp(ptr, arr, size+1));
> + kasan_int_result = __kasan_memcmp(ptr, arr, size+1));
> kfree(ptr);
> }
>
> --
> 2.29.2
>
--
Kees Cook
next prev parent reply other threads:[~2021-10-18 19:47 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-13 15:00 [PATCH 1/2] kasan: test: use underlying string helpers Arnd Bergmann
2021-10-13 15:00 ` [PATCH 2/2] kasan: use fortified strings for hwaddress sanitizer Arnd Bergmann
2021-10-18 19:57 ` Kees Cook
2021-10-18 20:09 ` Arnd Bergmann
2021-10-14 8:12 ` [PATCH 1/2] kasan: test: use underlying string helpers Vincenzo Frascino
2021-10-15 2:40 ` Kees Cook
2021-10-28 20:15 ` Andrew Morton
2021-10-28 20:42 ` Kees Cook
2021-10-18 19:47 ` Kees Cook [this message]
2021-10-18 19:55 ` Arnd Bergmann
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