From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757586AbZJHLFA (ORCPT ); Thu, 8 Oct 2009 07:05:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757545AbZJHLFA (ORCPT ); Thu, 8 Oct 2009 07:05:00 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:41274 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757216AbZJHLE7 (ORCPT ); Thu, 8 Oct 2009 07:04:59 -0400 Date: Wed, 7 Oct 2009 11:44:19 +0200 From: Pavel Machek To: Jan Beulich Cc: mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86-64: don't leak kernel register values to 32-bit processes Message-ID: <20091007094248.GA1425@ucw.cz> References: <4AC34D73020000780001744A@vpn.id2.novell.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AC34D73020000780001744A@vpn.id2.novell.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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... -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html