linux-kernel - Re: [PATCH] gcc4: Disable __compiletime_object

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Message-ID: <20131113202435.GB5322@roeck-us.net>
Date:	Wed, 13 Nov 2013 12:24:35 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Kees Cook <keescook@...omium.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gcc4: Disable __compiletime_object_size for GCC 4.6+

On Wed, Nov 13, 2013 at 10:39:13AM -0800, Kees Cook wrote:
> Hi Guenter,
> 
> On Fri, Apr 12, 2013 at 07:49:08PM -0700, Guenter Roeck wrote:
> > __builtin_object_size is known to be broken on gcc 4.6+.
> > See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48880 for details.
> > 
> > This causes unnecssary build warnings and errors such as
> > 
> > In function 'copy_from_user', inlined from 'sb16_copy_from_user'
> > 	at sound/oss/sb_audio.c:878:22:
> > arch/x86/include/asm/uaccess_32.h:211:26: error: call to 'copy_from_user_overflow'
> > 	declared with attribute error: copy_from_user() buffer size is not provably correct
> > make[3]: [sound/oss/sb_audio.o] Error 1 (ignored)
> > 
> > Disable it where broken.
> 
> Is there an alternative? This means that things like
> DEBUG_STRICT_USER_COPY_CHECKS are being rendered useless. I don't think
> this is _always_ broken, just under certain situations, right?
> 
There was a recent proposal to address the problem differently and then revert
this patch. Not sure what happened with it. I can try digging it up if necessary.

Guenter
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