linux-kernel - Re: [PATCH 1/2] build_bug.h: remove negative-array fallback for BUILD_BUG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAGXu5jJn5xRW6EqnULVESy1UZKjzxrxRAcHb412smtjoTVmsEQ@mail.gmail.com>
Date:   Fri, 16 Nov 2018 13:01:01 -0600
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] build_bug.h: remove negative-array fallback for BUILD_BUG_ON()

On Fri, Nov 16, 2018 at 12:19 AM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> The kernel can only be compiled with an optimization option (-O2, -Os,
> or the currently proposed -Og). Hence, __OPTIMIZE__ is always defined
> in the kernel source.
>
> A fallback for -O0 case is just hypothetical and pointless. Moreover,
> commit 0bb95f80a38f ("Makefile: Globally enable VLA warning") enabled
> -Wvla warning. The use of variable length arrays is banned.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>
>  include/linux/build_bug.h | 14 --------------
>  1 file changed, 14 deletions(-)
>
> diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
> index 43d1fd5..d415c64 100644
> --- a/include/linux/build_bug.h
> +++ b/include/linux/build_bug.h
> @@ -51,23 +51,9 @@
>   * If you have some code which relies on certain constants being equal, or
>   * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
>   * detect if someone changes it.
> - *
> - * The implementation uses gcc's reluctance to create a negative array, but gcc
> - * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to
> - * inline functions).  Luckily, in 4.3 they added the "error" function
> - * attribute just for this type of case.  Thus, we use a negative sized array
> - * (should always create an error on gcc versions older than 4.4) and then call
> - * an undefined function with the error attribute (should always create an
> - * error on gcc 4.3 and later).  If for some reason, neither creates a
> - * compile-time error, we'll still have a link-time error, which is harder to
> - * track down.
>   */
> -#ifndef __OPTIMIZE__
> -#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
> -#else
>  #define BUILD_BUG_ON(condition) \
>         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
> -#endif
>
>  /**
>   * BUILD_BUG - break compile if used.
> --
> 2.7.4
>



-- 
Kees Cook