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=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 9B2CFC433DB for ; Thu, 11 Feb 2021 10:37:13 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 4C73864E95 for ; Thu, 11 Feb 2021 10:37:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4C73864E95 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=merlin.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=tYfeMIYc9DUiylEr0epyYeWSbtM01mn/KE/lcb5Cqgk=; b=O1SJBDRpWPxrrSVup/R1GxSW2 TxOMSWPbEV6KaZGRwm9HaDk1So5ws/m5LPnE1TMbcBGc/f9W02rRoh1ekvwQL+tOG4mrDNKe1P6/3 JpNn4gCtIOK9tlMVTh46uNTKKnS4P3EyPD4Z9RcVY8ykwW6L+CJ4guiJVYmTFpoaY8X7oVdNlpSfw dLG0gQikH4rc+SUzIti+2WRpW/khav0SVPsFr8EoWi8CQRkoZHEYplrYgaI6U4SJ0yhjqrNz/Acvr hLMq1Y4Mvfp9yU9w30IMRQuagdfSgym+1h/uUnxL6Dz1r0PhKwTEjq8B21KGgLTmIhzDBtw4tqg1F ebgqHqstw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1lA9Jw-0004QT-UK; Thu, 11 Feb 2021 10:35:36 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1lA9Ju-0004Ps-CB for linux-arm-kernel@lists.infradead.org; Thu, 11 Feb 2021 10:35:35 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id DCA6D64E8B; Thu, 11 Feb 2021 10:35:31 +0000 (UTC) Date: Thu, 11 Feb 2021 10:35:29 +0000 From: Catalin Marinas To: Luis Machado Subject: Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Message-ID: <20210211103528.GA12106@arm.com> References: <20210210180316.23654-1-catalin.marinas@arm.com> <0916e89e-46b5-6002-7f9d-5d1df9e3e205@linaro.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0916e89e-46b5-6002-7f9d-5d1df9e3e205@linaro.org> 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-20210211_053534_485527_EF72BFD8 X-CRM114-Status: GOOD ( 17.23 ) 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: Kevin Brodsky , stable@vger.kernel.org, Steven Price , David Spickett , Vincenzo Frascino , Will Deacon , linux-arm-kernel@lists.infradead.org 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 Wed, Feb 10, 2021 at 03:52:18PM -0300, Luis Machado wrote: > On 2/10/21 3:03 PM, Catalin Marinas wrote: > > The ptrace(PTRACE_PEEKMTETAGS) implementation checks whether the user > > page has valid tags (mapped with PROT_MTE) by testing the PG_mte_tagged > > page flag. If this bit is cleared, ptrace(PTRACE_PEEKMTETAGS) returns > > -EIO. > > > > A newly created (PROT_MTE) mapping points to the zero page which had its > > tags zeroed during cpu_enable_mte(). If there were no prior writes to > > this mapping, ptrace(PTRACE_PEEKMTETAGS) fails with -EIO since the zero > > page does not have the PG_mte_tagged flag set. > > > > Set PG_mte_tagged on the zero page when its tags are cleared during > > boot. In addition, to avoid ptrace(PTRACE_PEEKMTETAGS) succeeding on > > !PROT_MTE mappings pointing to the zero page, change the > > __access_remote_tags() check to (vm_flags & VM_MTE) instead of > > PG_mte_tagged. > > > > Signed-off-by: Catalin Marinas > > Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") > > Cc: # 5.10.x > > Cc: Will Deacon > > Reported-by: Luis Machado [...] > Thanks. I gave this a try and it works as expected. So memory that is > PROT_MTE but has not been accessed yet can be inspected with PEEKMTETAGS > without getting an EIO back. Thanks. I assume I can add your tested-by. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel