linux-kernel - Re: [PATCH] x86-64: don't leak kernel register values to 32-bit processes

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: <4ACE364E.8090000@zytor.com>
Date:	Thu, 08 Oct 2009 11:58:22 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pavel Machek <pavel@....cz>
CC:	Jan Beulich <JBeulich@...ell.com>, mingo@...e.hu,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64: don't leak kernel register values to 32-bit	processes

On 10/07/2009 02:44 AM, Pavel Machek wrote:
> Hi!
> 
>> While 32-bit processes can't directly access R8...R15, they can gain
>> access to these registers by temporarily switching themselves into
>> 64-bit mode. Therefore, registers not preserved anyway by called C
>> functions (i.e. R8...R11) must be cleared prior to returning to user
>> mode.
> 
> How can userspace "temporarily switch itself" to 64bit mode?
> 
> Such ability would lead to very interesting behaviour on 32-bit
> kernel, I'd say...

You can only do so with a 64-bit kernel, but on a 64-bit kernel you can
do it by executing a far jump to segment USER_CS (0x33).

	-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/