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=-10.2 required=3.0 tests=BAYES_00, 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 A45D2C49EA2 for ; Fri, 18 Jun 2021 14:40:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8AB7161154 for ; Fri, 18 Jun 2021 14:40:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234616AbhFROme (ORCPT ); Fri, 18 Jun 2021 10:42:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:39244 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234595AbhFROm2 (ORCPT ); Fri, 18 Jun 2021 10:42:28 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id EF63061260; Fri, 18 Jun 2021 14:40:15 +0000 (UTC) Date: Fri, 18 Jun 2021 15:40:13 +0100 From: Catalin Marinas To: Steven Price Cc: Marc Zyngier , 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 , Andrew Jones Subject: Re: [PATCH v16 1/7] arm64: mte: Handle race when synchronising tags Message-ID: <20210618144013.GE16116@arm.com> References: <20210618132826.54670-1-steven.price@arm.com> <20210618132826.54670-2-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210618132826.54670-2-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 18, 2021 at 02:28:20PM +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") > Reviewed-by: Catalin Marinas > Signed-off-by: Steven Price Although I reviewed this patch, I think we should drop it from this series and restart the discussion with the Chromium guys on what/if they need PROT_MTE with MAP_SHARED. It currently breaks if you have two PROT_MTE mappings but if they are ok with only one of the mappings being PROT_MTE, I'm happy to just document it. Not sure whether subsequent patches depend on it though. -- Catalin