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

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Date:	Wed, 13 Nov 2013 12:57:13 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kees Cook <keescook@...omium.org>,
	Guenter Roeck <linux@...ck-us.net>
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 11/13/2013 10:39 AM, 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?
> 

It would be one thing to block it for, say, gcc 4.6 and 4.7 only, but
without an upper cap I don't think this is at all okay.

	-hpa


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