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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 ACC27C433DB for ; Tue, 23 Mar 2021 16:48:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8786F619C0 for ; Tue, 23 Mar 2021 16:48:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233299AbhCWQsQ (ORCPT ); Tue, 23 Mar 2021 12:48:16 -0400 Received: from foss.arm.com ([217.140.110.172]:49154 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233216AbhCWQsH (ORCPT ); Tue, 23 Mar 2021 12:48:07 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A1B27D6E; Tue, 23 Mar 2021 09:48:06 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.24.204]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8B7063F718; Tue, 23 Mar 2021 09:48:04 -0700 (PDT) Date: Tue, 23 Mar 2021 16:48:01 +0000 From: Mark Rutland To: "Madhavan T. Venkataraman" Cc: broonie@kernel.org, jpoimboe@redhat.com, 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 Subject: Re: [RFC PATCH v2 5/8] arm64: Detect an FTRACE frame and mark a stack trace unreliable Message-ID: <20210323164801.GE98545@C02TD0UTHF1T.local> References: <5997dfe8d261a3a543667b83c902883c1e4bd270> <20210315165800.5948-1-madvenka@linux.microsoft.com> <20210315165800.5948-6-madvenka@linux.microsoft.com> <20210323105118.GE95840@C02TD0UTHF1T.local> <2167f3c5-e7d0-40c8-99e3-ae89ceb2d60e@linux.microsoft.com> <20210323133611.GB98545@C02TD0UTHF1T.local> <20210323145734.GD98545@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 23, 2021 at 10:26:50AM -0500, Madhavan T. Venkataraman wrote: > On 3/23/21 9:57 AM, Mark Rutland wrote: > Thanks for explaining the nesting. It is now clear to me. No problem! > So, my next question is - can we define a practical limit for the > nesting so that any nesting beyond that is fatal? The reason I ask is > - if there is a max, then we can allocate an array of stack frames out > of band for the special frames so they are not part of the stack and > will not likely get corrupted. I suspect we can't define such a fatal limit without introducing a local DoS vector on some otherwise legitimate workload, and I fear this will further complicate the entry/exit logic, so I'd prefer to avoid introducing a new limit. What exactly do you mean by a "special frame", and why do those need additional protection over regular frame records? > Also, we don't have to do any special detection. If the number of out > of band frames used is one or more then we have exceptions and the > stack trace is unreliable. What is expected to protect against? Thanks, Mark.