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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 A39ABC43603 for ; Tue, 17 Dec 2019 17:56:20 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 7498E206EC for ; Tue, 17 Dec 2019 17:56:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Ue7hRuw8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7498E206EC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject: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=OP8sprhz4BPPuvKL0RykgHYjixq5IkmuAcqRTJgNNM0=; b=Ue7hRuw8XqoRZC RtiOUHmSFWv+WwJeur/mzLBI+I4nkCTHz8Uks0GY3hrvbOvCY6Tp7mePB/anwgFieYKjHoUD9/9vA J8tPu0uJj4WmlshnNtW1Ha2BcOIw54DiMEe2Y9nNL0ifztXaKkbHdpiYRVECRUOVSz+zc8TWQrbP3 N4jNRaQpelGtD+JF7PfrGdfJtwDYMMBae5H5RJ16JOdKWq84CPXAjDJr9aU5IhZIlpyPiD58niR9W ny3qh935u0bqwcUGf0EWV9hSelw4VqBkUsJ/WkgABj+SvmCAW4hTgY+dCdgCLb4veYFrIDqzFKQka DsuPbnAsyxxl0vNs9ipQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1ihH50-0001dJ-5v; Tue, 17 Dec 2019 17:56:18 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1ihH4x-0001ci-Fy for linux-arm-kernel@lists.infradead.org; Tue, 17 Dec 2019 17:56:17 +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 BC65230E; Tue, 17 Dec 2019 09:56:14 -0800 (PST) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.197.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 37C283F67D; Tue, 17 Dec 2019 09:56:13 -0800 (PST) Date: Tue, 17 Dec 2019 17:56:11 +0000 From: Catalin Marinas To: Peter Collingbourne Subject: Re: [PATCH 20/22] arm64: mte: Allow user control of the excluded tags via prctl() Message-ID: <20191217175610.GN5624@arrakis.emea.arm.com> References: <20191211184027.20130-1-catalin.marinas@arm.com> <20191211184027.20130-21-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191217_095615_579666_9203EA5D X-CRM114-Status: GOOD ( 21.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Richard Earnshaw , Branislav Rankov , Szabolcs Nagy , Marc Zyngier , Kevin Brodsky , linux-mm@kvack.org, Andrey Konovalov , Vincenzo Frascino , Will Deacon , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Dec 16, 2019 at 09:30:36AM -0800, Peter Collingbourne wrote: > On Mon, Dec 16, 2019 at 6:20 AM Kevin Brodsky wrote: > > In this patch, the default exclusion mask remains 0 (i.e. all tags can be generated). > > After some more discussions, Branislav and I think that it would be better to start > > with the reverse, i.e. all tags but 0 excluded (mask = 0xfe or 0xff). So with mask 0xff, IRG generates only tag 0? This seems to be the case reading the pseudocode in the ARM ARM. > > This should simplify the MTE setup in the early C runtime quite a bit. Indeed, if all > > tags can be generated, doing any heap or stack tagging before the > > PR_SET_TAGGED_ADDR_CTRL prctl() is issued can cause problems, notably because tagged > > addresses could end up being passed to syscalls. Conversely, if IRG and ADDG never > > set the top byte by default, then tagging operations should be no-ops until the > > prctl() is issued. This would be particularly useful given that it may not be > > straightforward for the C runtime to issue the prctl() before doing anything else. > > > > Additionally, since the default tag checking mode is PR_MTE_TCF_NONE, it would make > > perfect sense not to generate tags by default. > > > > Any thoughts? > > This would indeed allow the early C runtime startup code to pass > tagged addresses to syscalls, but I don't think it would entirely free > the code from the burden of worrying about stack tagging. Either way, > any stack frames that are active at the point when the prctl() is > issued would need to be compiled without stack tagging, because > otherwise those stack frames may use ADDG to rematerialize a stack > object address, which may produce a different address post-prctl. > Setting the exclude mask to 0xffff would at least make it more likely > for this problem to be detected, though. > > If we change the default in this way, maybe it would be worth > considering flipping the meaning of the tag mask and have it be a mask > of tags to allow. That would be consistent with the existing behaviour > where userspace sets bits in tagged_addr_ctrl in order to enable > tagging features. Either option works for me. It's really for the libc people to decide what they need. I think an "include" rather than "exclude" mask makes sense with the default 0 meaning only generate tag 0. Thanks. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel