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=-10.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 106D3C433ED for ; Wed, 5 May 2021 00:23:50 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7FDCB613CB for ; Wed, 5 May 2021 00:23:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7FDCB613CB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=yGCY44PzO+t0sR0eE9C5PFzZdQpNdTSFOoa/SDU9CoI=; b=NESZ1/7cR67R2OHip814ZlPLR aHNI0ABKGUQXW0+siuWjYY7ncCQJCjRU2Onp1nxHV0Gw1WwZoGmVvydtP3bZ0S0LKkv+/ZB9w72Qy 7GH6So2/eo43UaQRfN8Ky1+9N2qTFqKk6llEIZqNtoTJYBhIkLgAUrOFS3JW14IRHU0gVUz6m7GrP JyUVUOEfw7F3JlieW8sGvl+luelNnKpqWNAntMpTrF1Z+gTskyEwNBcr/+nWxjV7OCTelNb8xeW4g u7O2tU1dyOHlvRjzRbfozIPksA4Ny8feBCwZGZxrqWNPrJumUfjIRU0RqY8Jqfihr7F3Wz9NWZ8DM O2kHPnoHw==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1le5IQ-00HRGH-Ip; Wed, 05 May 2021 00:21:47 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1le5IM-00HREf-Ux for linux-arm-kernel@desiato.infradead.org; Wed, 05 May 2021 00:21:44 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To: Subject:Sender:Reply-To:Content-ID:Content-Description; bh=67pUuO9NPGqjJ/qDqrzzpbBgFlanoF6KUFDz7lH6P00=; b=1TXzlf5v9MD4b7LvOgayE0wHhr TJM1YtGgSEypXFBEdoTPRBPDFeQ0sKrmCBfGuqNC5YTZ/wDCaDwwZ+80igAPVpJ65hKzegi1swbV8 yFyXExgmRqAaRpZ2vi1eF4vaz1s5ff9v1sM+iySuFjPdejcHdvgWnqd3EBe1q7nA20A6sUIiCu5bh 6RW6cH6RYWtZxcj6kFkYfsxo3+CA1TXjFg/AZqsBeLdtAhxiapZ+S9JmXa4gUsnmMB7dl7h4Jp1iV ic9UEg70WaTpO3DN2YuBBUbrz/6Lz9yeCM/u4SGHRGm0dGpiUaTv1y6S4mx660AloJcL9eYZaDjp1 gGxF80yQ==; Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1le5IK-004Lvi-DJ for linux-arm-kernel@lists.infradead.org; Wed, 05 May 2021 00:21:41 +0000 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-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210504_172140_507987_96E22616 X-CRM114-Status: GOOD ( 18.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel