linux-kernel - Re: Fw: asm-x86/byteorder.h, CONFIG_X86

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <488B555F.4090709@zytor.com>
Date:	Sat, 26 Jul 2008 12:48:31 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Harvey Harrison <harvey.harrison@...il.com>
CC:	Olaf Hering <olaf@...fle.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Fw: asm-x86/byteorder.h, CONFIG_X86_BSWAP leaks to userland

Harvey Harrison wrote:
>>
>> An undefined CONFIG_foo defaults to 0 (I think), so bswap is never used.
>> Is this done on purpose, or can the CONFIG_ foo be moved inside
>> __KERNEL__ somehow?
> 
> I believe it's there to prevent the bswap instruction from being used on
> early x86_32 models (i386/i486).  As this will be 0 in userspace it is
> effectively never using the bswap instruction for these routines.
> 

i386, specifically.

However, you shouldn't leak these symbols to userspace; there is a 
warning option in gcc for undefined macros, and it's a *good thing* to 
use it.  Causing warnings in user space is not nice.

> I'm not sure if it's time yet to make the bswap ones be exported, as they
> would no longer be usable for those early machines.  X86 guys CC:d.

On i386 we still default to i386-compatible binaries; I *think* gcc has 
macros telling you if the user has used -march=i486 etc.

	-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/