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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 CFE6DC433DB for ; Tue, 23 Mar 2021 17:11:19 +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 52AAD619B2 for ; Tue, 23 Mar 2021 17:11:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 52AAD619B2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.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:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Vtoi4EnEWy+V/Q8ea+YCegty5SppGSkznAJRd7D8fF8=; b=g+8PopRkbSetKMKs1VrnjT7J/ VRDaoGpVmjUINAwHB86ykTkp/pXP3CH+ltc6+IuGnIrS7ctplU4C3R6+d2zW/sQBSK6U592+OhzjD A6ZmJXYeD4QtdKskzxlOW8l2P5gyo9IwqqZuiLfYkkA+PyPZ+8ZAvVhI/T5+EvoXM6XZyuiG65B// mgDNARltu92j/fUDmGyWOcJTJSZqSHBgJfHhiMxHJOyjl1+abNiJtjHsjm8w9bhMqAgoTHRUmhrNk i6VW204eNM6ea91dX39avGxP7NJQ6Bw+am8s5WI1Apl0mvxhXgfZN0moL1Z0FnLsQQf2vGEY7wwMp zx+OCsT8g==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lOkXA-00FMsD-3u; Tue, 23 Mar 2021 17:09:36 +0000 Received: from foss.arm.com ([217.140.110.172]) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lOkX6-00FMrj-Ey for linux-arm-kernel@lists.infradead.org; Tue, 23 Mar 2021 17:09:34 +0000 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 228B51042; Tue, 23 Mar 2021 10:09:30 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.24.204]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 103A53F718; Tue, 23 Mar 2021 10:09:27 -0700 (PDT) Date: Tue, 23 Mar 2021 17:09:25 +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: <20210323170925.GG98545@C02TD0UTHF1T.local> References: <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> <20210323164801.GE98545@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210323_170932_717034_C1947315 X-CRM114-Status: GOOD ( 18.33 ) 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 Tue, Mar 23, 2021 at 11:53:04AM -0500, Madhavan T. Venkataraman wrote: > On 3/23/21 11:48 AM, Mark Rutland wrote: > > On Tue, Mar 23, 2021 at 10:26:50AM -0500, Madhavan T. Venkataraman wrote: > >> 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. > >> 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? > > It is not a protection thing. I just wanted a reliable way to tell that there > is an exception without having to unwind the stack up to the exception frame. > That is all. I see. Given that's an optimization, we can consider doing something like that that after we have the functional bits in place, where we'll be in a position to see whether this is even a measureable concern in practice. I suspect that longer-term we'll end up trying to use metadata to unwind across exception boundaries, since it's possible to get blocked within those for long periods (e.g. for a uaccess fault), and the larger scale optimization for patching is to not block the patch. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel