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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 5AF4DC48BCD for ; Wed, 9 Jun 2021 10:33:43 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 2D2D561375 for ; Wed, 9 Jun 2021 10:33:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2D2D561375 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58462 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lqvWo-00037B-Bf for qemu-devel@archiver.kernel.org; Wed, 09 Jun 2021 06:33:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46240) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lqvU9-0007ov-69 for qemu-devel@nongnu.org; Wed, 09 Jun 2021 06:31:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:57508) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lqvU6-0006Jx-QC for qemu-devel@nongnu.org; Wed, 09 Jun 2021 06:30:56 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 81C06601FC; Wed, 9 Jun 2021 10:30:52 +0000 (UTC) Received: from 82-132-234-177.dab.02.net ([82.132.234.177] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lqvU2-006SNj-7g; Wed, 09 Jun 2021 11:30:50 +0100 Date: Wed, 09 Jun 2021 11:30:46 +0100 Message-ID: <875yynz5wp.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price Subject: Re: [PATCH v14 1/8] arm64: mte: Handle race when synchronising tags In-Reply-To: <20210607110816.25762-2-steven.price@arm.com> References: <20210607110816.25762-1-steven.price@arm.com> <20210607110816.25762-2-steven.price@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 82.132.234.177 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave.Martin@arm.com, mark.rutland@arm.com, tglx@linutronix.de, qemu-devel@nongnu.org, quintela@redhat.com, dgilbert@redhat.com, richard.henderson@linaro.org, peter.maydell@linaro.org, Haibo.Xu@arm.com, drjones@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Received-SPF: pass client-ip=198.145.29.99; envelope-from=maz@kernel.org; helo=mail.kernel.org X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Peter Maydell , "Dr. David Alan Gilbert" , Andrew Jones , Haibo Xu , Suzuki K Poulose , qemu-devel@nongnu.org, Catalin Marinas , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , James Morse , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 07 Jun 2021 12:08:09 +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 > --- > arch/arm64/kernel/mte.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index 125a10e413e9..a3583a7fd400 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 DEFINE_SPINLOCK(tag_sync_lock); > > #ifdef CONFIG_KASAN_HW_TAGS > /* Whether the MTE asynchronous mode is enabled. */ > @@ -34,13 +35,22 @@ EXPORT_SYMBOL_GPL(mte_async_mode); > > static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > { > + unsigned long flags; > pte_t old_pte = READ_ONCE(*ptep); > > + spin_lock_irqsave(&tag_sync_lock, flags); having though a bit more about this after an offline discussion with Catalin: why can't this lock be made per mm? We can't really share tags across processes anyway, so this is limited to threads from the same process. I'd also like it to be documented that page sharing can only reliably work with tagging if only one of the mappings is using tags. Thanks, M. -- Without deviation from the norm, progress is not possible.