From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755418AbdK2O4b convert rfc822-to-8bit (ORCPT ); Wed, 29 Nov 2017 09:56:31 -0500 Received: from smtp-out4.electric.net ([192.162.216.194]:51381 "EHLO smtp-out4.electric.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751929AbdK2O43 (ORCPT ); Wed, 29 Nov 2017 09:56:29 -0500 From: David Laight To: "'Andy Lutomirski'" , Peter Zijlstra CC: Ingo Molnar , Jarkko Nikula , linux-kernel , Andy Lutomirski , Thomas Gleixner , Linus Torvalds , Borislav Petkov Subject: RE: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled Thread-Topic: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled Thread-Index: AQHTaR8fKskq+GLGsUC5ju1OFMHHkKMrb/rw Date: Wed, 29 Nov 2017 14:56:43 +0000 Message-ID: <4f2c1cf45fd04e83a7d360d0d602830e@AcuMS.aculab.com> References: <0fede9f9-88b0-a6e7-1027-dfb2019b8ef2@linux.intel.com> <20171129070951.hjjjpbyilzaak4ig@gmail.com> <20171129124711.slmq5emx4f26c4zp@hirez.programming.kicks-ass.net> In-Reply-To: Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [fd9f:af1c:a25b:0:43c:695e:880f:8750] Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-Outbound-IP: 156.67.243.126 X-Env-From: David.Laight@ACULAB.COM X-Proto: esmtps X-Revdns: X-HELO: AcuMS.aculab.com X-TLS: TLSv1.2:ECDHE-RSA-AES256-SHA384:256 X-Authenticated_ID: X-PolicySMART: 3396946, 3397078 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. David