linux-kernel - Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc

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Date:   Tue, 23 Aug 2016 22:37:43 -0400
From:   Kees Cook <keescook@...omium.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern
 versions of gcc

On Tue, Aug 23, 2016 at 3:28 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> This is a revert of:
>
>   2fb0815c9ee6 ("gcc4: disable __compiletime_object_size for GCC 4.6+")
>
> The goal of that commit was to silence the "provably correct" gcc
> warnings.  But it went too far: it also disabled the runtime warnings.
>
> Now that the pretty much useless gcc warnings have been properly
> disposed of with the previous patch, re-enable this checking on modern
> versions of gcc so we can get the runtime warnings again.

As far as I know, this will still be broken since it's
__builtin_object_size() that is buggy. Maybe I'm misunderstanding
which piece is busted, though?

-Kees

>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  include/linux/compiler-gcc.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index e294939..e7f7a68 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -158,7 +158,7 @@
>  #define __compiler_offsetof(a, b)                                      \
>         __builtin_offsetof(a, b)
>
> -#if GCC_VERSION >= 40100 && GCC_VERSION < 40600
> +#if GCC_VERSION >= 40100
>  # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
>  #endif
>
> --
> 2.7.4
>



-- 
Kees Cook
Nexus Security