From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933803AbdK2QwJ (ORCPT ); Wed, 29 Nov 2017 11:52:09 -0500 Received: from mail.kernel.org ([198.145.29.99]:44966 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932149AbdK2QwH (ORCPT ); Wed, 29 Nov 2017 11:52:07 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F90B21998 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org X-Google-Smtp-Source: AGs4zMY8n5pVhZgiq4fYpMYxkPPQQHcsHXIna2vVuSfZORnNCkemNOMJFX4LgKKsLkdaIW54+pwKVVsVuX/Wj6xVwqI= MIME-Version: 1.0 In-Reply-To: References: <0fede9f9-88b0-a6e7-1027-dfb2019b8ef2@linux.intel.com> <20171129070951.hjjjpbyilzaak4ig@gmail.com> <20171129124711.slmq5emx4f26c4zp@hirez.programming.kicks-ass.net> <4f2c1cf45fd04e83a7d360d0d602830e@AcuMS.aculab.com> From: Andy Lutomirski Date: Wed, 29 Nov 2017 08:51:45 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled To: Andy Lutomirski Cc: David Laight , Peter Zijlstra , Ingo Molnar , Jarkko Nikula , linux-kernel , Thomas Gleixner , Linus Torvalds , Borislav Petkov 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 Wed, Nov 29, 2017 at 8:22 AM, Andy Lutomirski wrote: > On Wed, Nov 29, 2017 at 6:56 AM, David Laight wrote: >> From: Andy Lutomirski >>> Sent: 29 November 2017 14:34 >>> > On Nov 29, 2017, at 4:47 AM, Peter Zijlstra wrote: >>> > >>> >> On Wed, Nov 29, 2017 at 08:09:51AM +0100, Ingo Molnar wrote: >>> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >>> >> index f81d50d7ceac..c0b52df8ee4f 100644 >>> >> --- a/arch/x86/entry/entry_64.S >>> >> +++ b/arch/x86/entry/entry_64.S >>> >> @@ -945,16 +945,16 @@ idtentry simd_coprocessor_error do_simd_coprocessor_error >>> has_error_code=0 >>> >> */ >>> >> ENTRY(native_load_gs_index) >>> >> FRAME_BEGIN >>> >> + SWAPGS /* switch from user GS to kernel GS */ >>> >> pushfq >>> >> DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI) >>> >> TRACE_IRQS_OFF >>> >> - SWAPGS >>> > >>> > I'm thinking those moves it too far back; we should at least have >>> > interrupts disabled when we do SWAPGS, no? Also, curse paravirt. >>> > >>> >>> I'll look in a few hours. >>> >>> But we definitely can't have irqs on when running with user gs. >> >> I can't remember what happens when swapgs itself faults. >> I'm pretty sure it can, restoring %ds %es and %fs can definitely fault >> (especially for 32 bit apps) if the restored values are invalid. >> With user LDT I think it is possible for a valid segment register >> to become invalid while a process is sleeping. >> The debugger (and possible a signal handler) can set the segment >> registers to arbitrary values - so loading them faults. >> >> I fixed NetBSD a few years ago so that all these faults were handled >> correctly. > > SWAPGS never faults. > > I did test my patch, and I'm wondering how I missed the problem. Looking now... I think my patch was entirely correct and Jarkko's problem is some other bug. Lemme see if I can find it.