From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755497AbaD3E57 (ORCPT ); Wed, 30 Apr 2014 00:57:59 -0400 Received: from terminus.zytor.com ([198.137.202.10]:45517 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755146AbaD3E55 (ORCPT ); Wed, 30 Apr 2014 00:57:57 -0400 Message-ID: <536082CA.40905@zytor.com> Date: Tue, 29 Apr 2014 21:57:46 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Andi Kleen , Andy Lutomirski CC: x86@kernel.org, linux-kernel@vger.kernel.org, Andi Kleen Subject: Re: [PATCH 4/7] x86: Add support for rd/wr fs/gs base References: <1398723161-21968-1-git-send-email-andi@firstfloor.org> <1398723161-21968-5-git-send-email-andi@firstfloor.org> <535FED4D.5000703@amacapital.net> <20140429233950.GE2382@two.firstfloor.org> <53608180.5070800@zytor.com> In-Reply-To: <53608180.5070800@zytor.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/29/2014 09:52 PM, H. Peter Anvin wrote: > > It matters -- greatly -- if (and only if) we can enter the kernel with > usergs == kernelgs and then want to change usergs inside a paranoid > routine. At that point we risk being upside down, which basically means > we're rooted. > > However, I believe this patchset also means only IST entries can be > paranoid, which in turn means we can't sleep inside them. To the very > best of my knowledge the only times we change usergs is on context > switch or inside a system call. We need to make sure that is actually > the case, though. > > I'm at ELC for a few days, so I'll have limited decent-sized-monitor > time, but it shouldn't be too hard to convince ourselves of... mostly a > matter of making sure something like ptrace can't to stupid crap. > Just in case anyone is getting the wrong impression: this is a discussion about details. I'm glad to see this work getting done. -hpa