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From:   Marco Elver <elver@google.com>
Date:   Wed, 17 Nov 2021 08:00:00 +0100
Message-ID: <CANpmjNMdUJj3YZ6Bb-pDmcwe73axzuVpvQs_WNcQLnKBE-0Agw@mail.gmail.com>
Subject: Re: [PATCH] kasan: test: Silence intentional read overflow warnings
To:     Kees Cook <keescook@chromium.org>
Cc:     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
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Precedence: bulk

On Tue, 16 Nov 2021 at 01:41, Kees Cook <keescook@chromium.org> wrote:
> 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>

Acked-by: Marco Elver <elver@google.com>

Thanks for the quick fix!

> ---
>  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
>
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