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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 6C949C433ED for ; Mon, 17 May 2021 15:05:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CDCB611B0 for ; Mon, 17 May 2021 15:05:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241522AbhEQPHC (ORCPT ); Mon, 17 May 2021 11:07:02 -0400 Received: from foss.arm.com ([217.140.110.172]:54446 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239476AbhEQO5y (ORCPT ); Mon, 17 May 2021 10:57:54 -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 19BD2106F; Mon, 17 May 2021 07:56:36 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 815AE3F73B; Mon, 17 May 2021 07:56:33 -0700 (PDT) Subject: Re: [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags To: Marc Zyngier Cc: Catalin Marinas , Will Deacon , James Morse , Julien Thierry , Suzuki K Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Martin , Mark Rutland , Thomas Gleixner , qemu-devel@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , Richard Henderson , Peter Maydell , Haibo Xu , Andrew Jones References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-2-steven.price@arm.com> <87cztpv4mo.wl-maz@kernel.org> From: Steven Price Message-ID: <37fe19b5-6494-41c5-e541-ddc873a82be0@arm.com> Date: Mon, 17 May 2021 15:56:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <87cztpv4mo.wl-maz@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/05/2021 15:03, Marc Zyngier wrote: > Hi Steven, Hi Marc, > On Mon, 17 May 2021 13:32:32 +0100, > Steven Price wrote: >> >> mte_sync_tags() used test_and_set_bit() to set the PG_mte_tagged flag >> before restoring/zeroing the MTE tags. However if another thread were to >> race and attempt to sync the tags on the same page before the first >> thread had completed restoring/zeroing then it would see the flag is >> already set and continue without waiting. This would potentially expose >> the previous contents of the tags to user space, and cause any updates >> that user space makes before the restoring/zeroing has completed to >> potentially be lost. >> >> Since this code is run from atomic contexts we can't just lock the page >> during the process. Instead implement a new (global) spinlock to protect >> the mte_sync_page_tags() function. >> >> Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") >> Signed-off-by: Steven Price >> --- >> --- >> arch/arm64/kernel/mte.c | 21 ++++++++++++++++++--- >> 1 file changed, 18 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c >> index 125a10e413e9..c88e778c2fa9 100644 >> --- a/arch/arm64/kernel/mte.c >> +++ b/arch/arm64/kernel/mte.c >> @@ -25,6 +25,7 @@ >> u64 gcr_kernel_excl __ro_after_init; >> >> static bool report_fault_once = true; >> +static spinlock_t tag_sync_lock; > > What initialises this spinlock? Have you tried this with lockdep? I'd > expect it to be defined with DEFINE_SPINLOCK(), which always does the > right thing. You of course are absolute right, and this will blow up with lockdep. Sorry about that. DEFINE_SPINLOCK() solves the problem. Thanks, Steve