linux-kernel - Re: [PATCH] lib: test_ubsan: VLA no longer used in kernel

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Message-ID: <CAGXu5jLJF-uXFB5cVgc163VevYSUOGJNBOe8qb7rYFfs3xp+rw@mail.gmail.com>
Date:   Sun, 13 Jan 2019 16:16:10 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Olof Johansson <olof@...om.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jinbum Park <jinb.park7@...il.com>,
        Colin King <colin.king@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] lib: test_ubsan: VLA no longer used in kernel

On Sun, Jan 13, 2019 at 10:32 AM Olof Johansson <olof@...om.net> wrote:
>
> Since we now build with -Wvla, any use of VLA throws a warning.
> Including this test, so... maybe we should just remove the test?
>
> lib/test_ubsan.c: In function 'test_ubsan_vla_bound_not_positive':
> lib/test_ubsan.c:48:2: warning: ISO C90 forbids variable length array 'buf' [-Wvla]

I patched the Makefile to remove -Wvla for the *SAN tests. Something
recently seems to be stripping it from the build command line, though.
I haven't figured out what's going on...

-Kees

>
> For the out-of-bounds test, switch to non-VLA setup.
>
> lib/test_ubsan.c: In function 'test_ubsan_out_of_bounds':
> lib/test_ubsan.c:64:2: warning: ISO C90 forbids variable length array 'arr' [-Wvla]
>
> Cc: Colin Ian King <colin.king@...onical.com>
> Cc: Jinbum Park <jinb.park7@...il.com>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Signed-off-by: Olof Johansson <olof@...om.net>
>
> ---
>  lib/test_ubsan.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
>
> diff --git a/lib/test_ubsan.c b/lib/test_ubsan.c
> index 280f4979d00ed..9ea10adf7a66f 100644
> --- a/lib/test_ubsan.c
> +++ b/lib/test_ubsan.c
> @@ -42,14 +42,6 @@ static void test_ubsan_divrem_overflow(void)
>         val /= val2;
>  }
>
> -static void test_ubsan_vla_bound_not_positive(void)
> -{
> -       volatile int size = -1;
> -       char buf[size];
> -
> -       (void)buf;
> -}
> -
>  static void test_ubsan_shift_out_of_bounds(void)
>  {
>         volatile int val = -1;
> @@ -61,7 +53,7 @@ static void test_ubsan_shift_out_of_bounds(void)
>  static void test_ubsan_out_of_bounds(void)
>  {
>         volatile int i = 4, j = 5;
> -       volatile int arr[i];
> +       volatile int arr[4];
>
>         arr[j] = i;
>  }
> @@ -113,7 +105,6 @@ static const test_ubsan_fp test_ubsan_array[] = {
>         test_ubsan_mul_overflow,
>         test_ubsan_negate_overflow,
>         test_ubsan_divrem_overflow,
> -       test_ubsan_vla_bound_not_positive,
>         test_ubsan_shift_out_of_bounds,
>         test_ubsan_out_of_bounds,
>         test_ubsan_load_invalid_value,
> --
> 2.11.0
>


-- 
Kees Cook