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=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=no 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 0A954C43460 for ; Sun, 11 Apr 2021 17:54:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D4AF66108B for ; Sun, 11 Apr 2021 17:54:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236061AbhDKRyf (ORCPT ); Sun, 11 Apr 2021 13:54:35 -0400 Received: from linux.microsoft.com ([13.77.154.182]:59662 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233822AbhDKRyd (ORCPT ); Sun, 11 Apr 2021 13:54:33 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id 3744A20BCFB3; Sun, 11 Apr 2021 10:54:16 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 3744A20BCFB3 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1618163656; bh=MLtBefkHmjSmdpfbhYpvt4YGwNCxEie/Zvb95gWk5ZE=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=fujDV8OeM1T22IT97/wOcNnL1wdw/Nw2777lmGyZsnTrOqwx8PoSG7U1cVCZh+/bn Au7ugxlJ/Dtl6Q4ax/hesnnUSBn4RB1jjp4rNQTwWIEzzfdsNudvnl/ISWCQ4bUINk 0O+skF0BuBp2lmR/elC8XNenrzRFlJRmJ2nRqQj4= Subject: Re: [RFC PATCH v2 0/4] arm64: Implement stack trace reliability checks To: Josh Poimboeuf Cc: Mark Rutland , broonie@kernel.org, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra References: <705993ccb34a611c75cdae0a8cb1b40f9b218ebd> <20210405204313.21346-1-madvenka@linux.microsoft.com> <20210409120859.GA51636@C02TD0UTHF1T.local> <20210409213741.kqmwyajoppuqrkge@treble> <8c30ec5f-b51e-494f-5f6c-d2f012135f69@linux.microsoft.com> <20210409223227.rvf6tfhvgnpzmabn@treble> <20210409225321.2czbawz6p2aquf5m@treble> From: "Madhavan T. Venkataraman" Message-ID: <1be20ada-6b52-c6e8-508c-7572c438d2b7@linux.microsoft.com> Date: Sun, 11 Apr 2021 12:54:15 -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: <20210409225321.2czbawz6p2aquf5m@treble> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/9/21 5:53 PM, Josh Poimboeuf wrote: > On Fri, Apr 09, 2021 at 05:32:27PM -0500, Josh Poimboeuf wrote: >> On Fri, Apr 09, 2021 at 05:05:58PM -0500, Madhavan T. Venkataraman wrote: >>>> FWIW, over the years we've had zero issues with encoding the frame >>>> pointer on x86. After you save pt_regs, you encode the frame pointer to >>>> point to it. Ideally in the same macro so it's hard to overlook. >>>> >>> >>> I had the same opinion. In fact, in my encoding scheme, I have additional >>> checks to make absolutely sure that it is a true encoding and not stack >>> corruption. The chances of all of those values accidentally matching are, >>> well, null. >> >> Right, stack corruption -- which is already exceedingly rare -- would >> have to be combined with a miracle or two in order to come out of the >> whole thing marked as 'reliable' :-) >> >> And really, we already take a similar risk today by "trusting" the frame >> pointer value on the stack to a certain extent. > > Oh yeah, I forgot to mention some more benefits of encoding the frame > pointer (or marking pt_regs in some other way): > > a) Stack addresses can be printed properly: '%pS' for printing regs->pc > and '%pB' for printing call returns. > > Using '%pS' for call returns (as arm64 seems to do today) will result > in printing the wrong function when you have tail calls to noreturn > functions on the stack (which is actually quite common for calls to > panic(), die(), etc). > > More details: > > https://lkml.kernel.org/r/20210403155948.ubbgtwmlsdyar7yp@treble > > b) Stack dumps to the console can dump the exception registers they find > along the way. This is actually quite nice for debugging. > > Great. I am preparing version 3 taking into account comments from yourself, Mark Rutland and Mark Brown. Stay tuned. Madhavan