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=-19.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1, USER_IN_DEF_DKIM_WL 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 AF6A6C433ED for ; Wed, 5 May 2021 00:21:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 84411610A0 for ; Wed, 5 May 2021 00:21:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231134AbhEEAWe (ORCPT ); Tue, 4 May 2021 20:22:34 -0400 Received: from linux.microsoft.com ([13.77.154.182]:40700 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230505AbhEEAWe (ORCPT ); Tue, 4 May 2021 20:22:34 -0400 Received: from [192.168.254.32] (unknown [47.187.223.33]) by linux.microsoft.com (Postfix) with ESMTPSA id 0759C20B7178; Tue, 4 May 2021 17:21:37 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 0759C20B7178 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1620174098; bh=67pUuO9NPGqjJ/qDqrzzpbBgFlanoF6KUFDz7lH6P00=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=Cj/GF5no1DMzZUaaja0KNhnaQ6g3J95YGLHwQk/gdXf2RUxB/JCXv9g2OPWrRXuCl qM0WHBHB7DMIG/wVEbyC7+bwFsEZLYSxsIUgYznkroXl4AlWjKTZR3y4rv5wsai5+v vYXrukyB/VmQEH7FF4WOakI6azOsc9SeGD8nx0xA= Subject: Re: [RFC PATCH v3 1/4] arm64: Introduce stack trace reliability checks in the unwinder To: Josh Poimboeuf Cc: broonie@kernel.org, mark.rutland@arm.com, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <65cf4dfbc439b010b50a0c46ec500432acde86d6> <20210503173615.21576-1-madvenka@linux.microsoft.com> <20210503173615.21576-2-madvenka@linux.microsoft.com> <20210504215248.oi3zay3memgqri33@treble> <20210505000728.yxg3xbwa3emcu2wi@treble> From: "Madhavan T. Venkataraman" Message-ID: <2fc9a77a-ddf5-812a-0681-ece94b433d71@linux.microsoft.com> Date: Tue, 4 May 2021 19:21:37 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210505000728.yxg3xbwa3emcu2wi@treble> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 5/4/21 7:07 PM, Josh Poimboeuf wrote: > On Tue, May 04, 2021 at 06:13:39PM -0500, Madhavan T. Venkataraman wrote: >> >> >> On 5/4/21 4:52 PM, Josh Poimboeuf wrote: >>> On Mon, May 03, 2021 at 12:36:12PM -0500, madvenka@linux.microsoft.com wrote: >>>> @@ -44,6 +44,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) >>>> unsigned long fp = frame->fp; >>>> struct stack_info info; >>>> >>>> + frame->reliable = true; >>>> + >>> >>> Why set 'reliable' to true on every invocation of unwind_frame()? >>> Shouldn't it be remembered across frames? >>> >> >> This is mainly for debug purposes in case a caller wants to print the whole stack and also >> print which functions are unreliable. For livepatch, it does not make any difference. It will >> quit as soon as it encounters an unreliable frame. > > Hm, ok. So 'frame->reliable' refers to the current frame, not the > entire stack. > Yes. >>> Also, it looks like there are several error scenarios where it returns >>> -EINVAL but doesn't set 'reliable' to false. >>> >> >> I wanted to make a distinction between an error situation (like stack corruption where unwinding >> has to stop) and an unreliable situation (where unwinding can still proceed). E.g., when a >> stack trace is taken for informational purposes or debug purposes, the unwinding will try to >> proceed until either the stack trace ends or an error happens. > > Ok, but I don't understand how that relates to my comment. > > Why wouldn't a stack corruption like !on_accessible_stack() set > 'frame->reliable' to false? > I do see your point. If an error has been hit, then the stack trace is essentially unreliable regardless of anything else. So, I accept your comment. I will mark the stack trace as unreliable if any kind of error is encountered. Thanks! Madhavan