From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05507C43381 for ; Tue, 12 Mar 2019 12:05:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CAA5F206BA for ; Tue, 12 Mar 2019 12:05:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726452AbfCLMFj (ORCPT ); Tue, 12 Mar 2019 08:05:39 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:41218 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725873AbfCLMFj (ORCPT ); Tue, 12 Mar 2019 08:05:39 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4EB62374; Tue, 12 Mar 2019 05:05:38 -0700 (PDT) Received: from e107155-lin (e107155-lin.cambridge.arm.com [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 59EDC3F59C; Tue, 12 Mar 2019 05:05:35 -0700 (PDT) Date: Tue, 12 Mar 2019 12:05:29 +0000 From: Sudeep Holla To: "Haibo Xu (Arm Technology China)" Cc: "x86@kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , Catalin Marinas , Will Deacon , Oleg Nesterov , Paul Mackerras , Michael Ellerman , Thomas Gleixner , Ingo Molnar , Richard Weinberger , "jdike@addtoit.com" , Steve Capper , "Bin Lu (Arm Technology China)" , Andy Lutomirski , Borislav Petkov Subject: Re: [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall_enter hook Message-ID: <20190312120529.GA13825@e107155-lin> References: <20190228183220.15626-1-sudeep.holla@arm.com> <20190228183220.15626-4-sudeep.holla@arm.com> <20190304101205.GA1504@e107155-lin> <96d59a68-e5e2-86d9-c707-a79aad438b76@arm.com> <20190311183403.GA31062@e107155-lin> <65b00ea1-f784-4fb4-2a98-49fa44d9fa8f@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <65b00ea1-f784-4fb4-2a98-49fa44d9fa8f@arm.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 12, 2019 at 01:34:44AM +0000, Haibo Xu (Arm Technology China) wrote: > On 2019/3/12 2:34, Sudeep Holla wrote: > > (I thought I had sent this email, last Tuesday itself, but saw this in my > > draft today, something went wrong, sorry for the delay) > > > > On Tue, Mar 05, 2019 at 02:14:47AM +0000, Haibo Xu (Arm Technology China) wrote: > >> On 2019/3/4 18:12, Sudeep Holla wrote: > >>> On Mon, Mar 04, 2019 at 08:25:28AM +0000, Haibo Xu (Arm Technology China) wrote: > >>>> On 2019/3/1 2:32, Sudeep Holla wrote: > >>>>> Now that we have a new hook ptrace_syscall_enter that can be called from > >>>>> syscall entry code and it handles PTRACE_SYSEMU in generic code, we > >>>>> can do some cleanup using the same in syscall_trace_enter. > >>>>> > >>>>> Further the extra logic to find single stepping PTRACE_SYSEMU_SINGLESTEP > >>>>> in syscall_slow_exit_work seems unnecessary. Let's remove the same. > >>>> > >>>> I think we should not change the logic here. Is so, it will double the report of syscall > >>>> when PTRACE_SYSEMU_SINGLESTEP is enabled. > >>>> > >>> > >>> I don't think that should happen, but I may be missing something. > >>> Can you explain how ? > >>> > >> > >> When PTRACE_SYSEMU_SINGLESTEP is enabled, both the _TIF_SYSCALL_EMU and > >> _TIF_SINGLESTEP flags are set, but ptrace only need to report(send SIGTRAP) > >> at the entry of a system call, no need to report at the exit of a system > >> call. > >> > > Sorry, but I still not get it, we have: > > > > step = ((flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) == _TIF_SINGLESTEP); > > > > For me, this is same as: > > step = ((flags & _TIF_SINGLESTEP) == _TIF_SINGLESTEP) > > or > > if (flags & _TIF_SINGLESTEP) > > step = true; > > > > I don't think so! As I mentioned in the last email loop, when > PTRACE_SYSEMU_SINGLESTE is enabled, both the _TIF_SYSCALL_EMU and > _TIF_SINGLESTEP flags are set, in which case the step should be "false" for > the old logic. But with the new logic, the step is "true". > Ah right, sorry I missed that. > > So when PTRACE_SYSEMU_SINGLESTEP, _TIF_SYSCALL_EMU and _TIF_SINGLESTEP > > are set and step evaluates to true. > > > > So dropping _TIF_SYSCALL_EMU here should be fine. Am I still missing > > something ? > > > > -- > > Regards, > > Sudeep > > > > For the PTRACE_SYSEMU_SINGLESTEP request, ptrace only need to report(send > SIGTRAP) at the entry of a system call, no need to report at the exit of a > system call.That's why the old logic-{step = ((flags & (_TIF_SINGLESTEP | > _TIF_SYSCALL_EMU)) == _TIF_SINGLESTEP)} here try to filter out the special > case(PTRACE_SYSEMU_SINGLESTEP). > Understood > Another way to make sure the logic is fine, you can run some tests with > respect to both logic, and to check whether they have the same behavior. > I did run selftests after Andy Lutomirski pointed out. Nothing got flagged, I haven't looked at the tests themselves yet, but it clearly misses this case. -- Regards, Sudeep