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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 1EFE0C433B4 for ; Wed, 5 May 2021 00:07:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBDB0613CD for ; Wed, 5 May 2021 00:07:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231182AbhEEAIe (ORCPT ); Tue, 4 May 2021 20:08:34 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:50434 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231147AbhEEAId (ORCPT ); Tue, 4 May 2021 20:08:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620173257; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=WLuhQI1mHvbvNctH59ASrVI5S/Q5ccQ6XIJwhLh2EGQ=; b=a6r02xRcuu5O6RUuXZJrjW6miPc5j3A+JrpHe9U+WuPt+aWkM2MOt0hYGxdpv3kfE/BiaG eI/OsI6cOuWdvibvBEotkPlbgMTU6jwKiZUeh/1lM2M1D1vu39tAOPZZEnbS0NXbruwG0l jYNpYMz+rq7yC75xA6cuh0H5YVHNkSc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-442-axtACvBCMI65Emy9o77H0g-1; Tue, 04 May 2021 20:07:35 -0400 X-MC-Unique: axtACvBCMI65Emy9o77H0g-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EF2E5801817; Wed, 5 May 2021 00:07:33 +0000 (UTC) Received: from treble (ovpn-115-93.rdu2.redhat.com [10.10.115.93]) by smtp.corp.redhat.com (Postfix) with SMTP id DF02560C4A; Wed, 5 May 2021 00:07:28 +0000 (UTC) Date: Tue, 4 May 2021 19:07:28 -0500 From: Josh Poimboeuf To: "Madhavan T. Venkataraman" 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 Subject: Re: [RFC PATCH v3 1/4] arm64: Introduce stack trace reliability checks in the unwinder Message-ID: <20210505000728.yxg3xbwa3emcu2wi@treble> References: <65cf4dfbc439b010b50a0c46ec500432acde86d6> <20210503173615.21576-1-madvenka@linux.microsoft.com> <20210503173615.21576-2-madvenka@linux.microsoft.com> <20210504215248.oi3zay3memgqri33@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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? In other words: for livepatch purposes, how does the caller tell the difference between hitting the final stack record -- which returns an error with reliable 'true' -- and a stack corruption like !on_accessible_stack(), which also returns an error with reliable 'true'? Surely the latter should be considered unreliable? -- Josh