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 05AA5C48BDF for ; Fri, 18 Jun 2021 14:40:25 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 79D4961351 for ; Fri, 18 Jun 2021 14:40:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 79D4961351 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 091B54B0BD; Fri, 18 Jun 2021 10:40:24 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 5mk7y7ap3skS; Fri, 18 Jun 2021 10:40:22 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id BF85C4B085; Fri, 18 Jun 2021 10:40:22 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 0DEF84B085 for ; Fri, 18 Jun 2021 10:40:21 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id yPQMRYy0sdT9 for ; Fri, 18 Jun 2021 10:40:20 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 020BD407E7 for ; Fri, 18 Jun 2021 10:40:19 -0400 (EDT) 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 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-Disposition: inline In-Reply-To: <20210618132826.54670-2-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm