Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752614AbaDVXJI (ORCPT ); Tue, 22 Apr 2014 19:09:08 -0400 Received: from mail-lb0-f170.google.com ([209.85.217.170]:54849 "EHLO mail-lb0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751034AbaDVXIu (ORCPT ); Tue, 22 Apr 2014 19:08:50 -0400 MIME-Version: 1.0 In-Reply-To: <5356CE58.1090502@zytor.com> References: <20140422144659.GF15882@pd.tnic> <53569467.1030809@zytor.com> <5356A70A.5090907@zytor.com> <5356AF9F.4010301@zytor.com> <5356BA2F.2030007@zytor.com> <5356CE58.1090502@zytor.com> Date: Tue, 22 Apr 2014 19:08:48 -0400 Message-ID: Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE* From: Brian Gerst To: "H. Peter Anvin" Cc: Andrew Lutomirski , Linus Torvalds , Borislav Petkov , "H. Peter Anvin" , Linux Kernel Mailing List , Ingo Molnar , Alexander van Heukelum , Konrad Rzeszutek Wilk , Boris Ostrovsky , Arjan van de Ven , Alexandre Julliard , Andi Kleen , Thomas Gleixner Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 22, 2014 at 4:17 PM, H. Peter Anvin wrote: > On 04/22/2014 12:55 PM, Brian Gerst wrote: >> On Tue, Apr 22, 2014 at 2:51 PM, H. Peter Anvin wrote: >>> On 04/22/2014 11:17 AM, Brian Gerst wrote: >>>>> >>>>> That is the entry condition that we have to deal with. The fact that >>>>> the switch to the IST is unconditional is what makes ISTs hard to deal with. >>>> >>>> Right, that is why you switch away from the IST as soon as possible, >>>> copying the data that is already pushed there to another stack so it >>>> won't be overwritten by a recursive fault. >>>> >>> >>> That simply will not work if you can take a #GP due to the "safe" MSR >>> functions from NMI and #MC context, which would be my main concern. >> >> In that case (#2 above), you would switch to the previous %rsp (in the >> NMI/MC stack), copy the exception frame from the IST, and continue >> with the #GP handler. That effectively is the same as it is today, >> where no stack switch occurs on the #GP fault. >> > > 1. You take #GP. This causes an IST stack switch. > 2. You immediately thereafter take an NMI. This switches stacks again. > 3. Now you take another #GP. This causes another IST stack, and now you > have clobbered your return information, and cannot resume. You are right. That will not work. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/