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,URIBL_BLOCKED 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 14CF9C433B4 for ; Mon, 17 May 2021 14:04:17 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 8905261209 for ; Mon, 17 May 2021 14:04:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8905261209 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 044D84B54D; Mon, 17 May 2021 10:04:16 -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 m9Tr7eMZ21Ln; Mon, 17 May 2021 10:04:10 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id E26CC4B572; Mon, 17 May 2021 10:04:10 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 8D1F64B4A6 for ; Mon, 17 May 2021 10:04:09 -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 6Sagx36OSQP5 for ; Mon, 17 May 2021 10:04:05 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 4AE244B24E for ; Mon, 17 May 2021 10:04:05 -0400 (EDT) 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 4AB6561074; Mon, 17 May 2021 14:04:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] 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 1lidqj-001ouz-3j; Mon, 17 May 2021 15:04:01 +0100 Date: Mon, 17 May 2021 15:03:59 +0100 Message-ID: <87cztpv4mo.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price Subject: Re: [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags In-Reply-To: <20210517123239.8025-2-steven.price@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-2-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") X-SA-Exim-Connect-IP: 62.31.163.78 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 Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Catalin Marinas , 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 Hi Steven, 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. > > #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); > + > + /* Recheck with the lock held */ > + if (test_bit(PG_mte_tagged, &page->flags)) > + goto out; > + > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > - return; > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > + goto out; > + } > } > > page_kasan_tag_reset(page); > @@ -53,6 +63,10 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > */ > smp_wmb(); > mte_clear_page_tags(page_address(page)); > + set_bit(PG_mte_tagged, &page->flags); > + > +out: > + spin_unlock_irqrestore(&tag_sync_lock, flags); > } > > void mte_sync_tags(pte_t *ptep, pte_t pte) > @@ -60,10 +74,11 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > + if (!test_bit(PG_mte_tagged, &page->flags)) > mte_sync_page_tags(page, ptep, check_swap); > } > } Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-14.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 43AA9C433B4 for ; Mon, 17 May 2021 14:13:27 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 BD2516157E for ; Mon, 17 May 2021 14:13:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BD2516157E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To:Subject:Cc:To: From:Message-ID:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9m5xqTi0z+/OAS6emgwUx50gf8WjrrASPwSkM9XRMDw=; b=dx1B9NYBJNyDla8QLqEcz0b+N ePX9hCQIsZR1BxOO+N5LW+XhkN/3SQ6O2vbf4Wzg51xMwSbNYkmb4JPCL2OW92rkxpEWRgcGl/CmM bItTQY5Kx+57AfCu31LEoFTv2DW7wjQzl9Y4tqbln+0YkFKZESmrlamu8vJWOfOBh+F/ctEVSvapN QbpB2iDqJWwhMwWRpEW0E4Ao86kfJxXKbZGLME/VUZrwL7nW+X1egY90vr4yinf8rIrhbU7CEYJAb fcY70kvzhvvQYEC9sPsgD7V5hmy/9Iu2OvLLSCdfgYmFoCtKBz512AN6azX7XAmMbEtXNttQ/buK4 hEMMXHCBg==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lidxp-00FBfs-3D; Mon, 17 May 2021 14:11:21 +0000 Received: from bombadil.infradead.org ([198.137.202.133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lidrA-00FAYL-Nb for linux-arm-kernel@desiato.infradead.org; Mon, 17 May 2021 14:05:10 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Type:MIME-Version:References: In-Reply-To:Subject:Cc:To:From:Message-ID:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=QilfV3N7B2/mBZ5jiLY/GHMegnDBhr17qmrrGxZE0SQ=; b=e+8wL0wVC6VIfdgPuMHTgRMn/L jzAN/3d5cFf32Znaz3McsbVRLy1+j7PYzaqgxZwGSOQRIWgjZAUuLpxFwsR/mXSBRe1LXTCAvD4mu QIPm+i4rRi0fzbipg7nQj2OVon8wF7sEc1qvSARHdh6dixvb8HQ2OVmiZxK6uAtswvtccoAg/CgfR JF/xNBE6j89AYd0atof9nw93DjB1aTCSRlLd1BAy7V4YtfgApjdkl7P7twQNmHVPnPN/n5S0t+pud 6xFZ4wHZJs9KzXCZ79TA3tLDiIDUk9eMQPnk6f5xhnIe8lxIKYLD+MsDee+ITs2sOyELCr+nIdniO SIBxzveg==; Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lidqm-00DpEL-KJ for linux-arm-kernel@lists.infradead.org; Mon, 17 May 2021 14:04:20 +0000 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 4AB6561074; Mon, 17 May 2021 14:04:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] 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 1lidqj-001ouz-3j; Mon, 17 May 2021 15:04:01 +0100 Date: Mon, 17 May 2021 15:03:59 +0100 Message-ID: <87cztpv4mo.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price 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 Subject: Re: [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags In-Reply-To: <20210517123239.8025-2-steven.price@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-2-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") X-SA-Exim-Connect-IP: 62.31.163.78 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210517_070404_834684_913A47CA X-CRM114-Status: GOOD ( 32.57 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Hi Steven, 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. > > #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); > + > + /* Recheck with the lock held */ > + if (test_bit(PG_mte_tagged, &page->flags)) > + goto out; > + > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > - return; > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > + goto out; > + } > } > > page_kasan_tag_reset(page); > @@ -53,6 +63,10 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > */ > smp_wmb(); > mte_clear_page_tags(page_address(page)); > + set_bit(PG_mte_tagged, &page->flags); > + > +out: > + spin_unlock_irqrestore(&tag_sync_lock, flags); > } > > void mte_sync_tags(pte_t *ptep, pte_t pte) > @@ -60,10 +74,11 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > + if (!test_bit(PG_mte_tagged, &page->flags)) > mte_sync_page_tags(page, ptep, check_swap); > } > } Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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,URIBL_BLOCKED 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 35819C433B4 for ; Mon, 17 May 2021 14:04:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0EAAF61241 for ; Mon, 17 May 2021 14:04:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237822AbhEQOF4 (ORCPT ); Mon, 17 May 2021 10:05:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:55446 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237810AbhEQOFU (ORCPT ); Mon, 17 May 2021 10:05:20 -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 4AB6561074; Mon, 17 May 2021 14:04:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] 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 1lidqj-001ouz-3j; Mon, 17 May 2021 15:04:01 +0100 Date: Mon, 17 May 2021 15:03:59 +0100 Message-ID: <87cztpv4mo.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price 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 Subject: Re: [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags In-Reply-To: <20210517123239.8025-2-steven.price@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-2-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: 62.31.163.78 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steven, 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. > > #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); > + > + /* Recheck with the lock held */ > + if (test_bit(PG_mte_tagged, &page->flags)) > + goto out; > + > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > - return; > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > + goto out; > + } > } > > page_kasan_tag_reset(page); > @@ -53,6 +63,10 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > */ > smp_wmb(); > mte_clear_page_tags(page_address(page)); > + set_bit(PG_mte_tagged, &page->flags); > + > +out: > + spin_unlock_irqrestore(&tag_sync_lock, flags); > } > > void mte_sync_tags(pte_t *ptep, pte_t pte) > @@ -60,10 +74,11 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > + if (!test_bit(PG_mte_tagged, &page->flags)) > mte_sync_page_tags(page, ptep, check_swap); > } > } Thanks, M. -- Without deviation from the norm, progress is not possible. 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,URIBL_BLOCKED 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 B63C0C433B4 for ; Mon, 17 May 2021 14:05:46 +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 34B2361221 for ; Mon, 17 May 2021 14:05:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 34B2361221 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]:39830 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lidsP-0000Me-2F for qemu-devel@archiver.kernel.org; Mon, 17 May 2021 10:05:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51404) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lidqq-0007sb-S4 for qemu-devel@nongnu.org; Mon, 17 May 2021 10:04:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:44160) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lidqo-00083O-Q2 for qemu-devel@nongnu.org; Mon, 17 May 2021 10:04:08 -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 4AB6561074; Mon, 17 May 2021 14:04:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] 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 1lidqj-001ouz-3j; Mon, 17 May 2021 15:04:01 +0100 Date: Mon, 17 May 2021 15:03:59 +0100 Message-ID: <87cztpv4mo.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price Subject: Re: [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags In-Reply-To: <20210517123239.8025-2-steven.price@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-2-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: 62.31.163.78 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" Hi Steven, 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. > > #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); > + > + /* Recheck with the lock held */ > + if (test_bit(PG_mte_tagged, &page->flags)) > + goto out; > + > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > - return; > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > + goto out; > + } > } > > page_kasan_tag_reset(page); > @@ -53,6 +63,10 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > */ > smp_wmb(); > mte_clear_page_tags(page_address(page)); > + set_bit(PG_mte_tagged, &page->flags); > + > +out: > + spin_unlock_irqrestore(&tag_sync_lock, flags); > } > > void mte_sync_tags(pte_t *ptep, pte_t pte) > @@ -60,10 +74,11 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > + if (!test_bit(PG_mte_tagged, &page->flags)) > mte_sync_page_tags(page, ptep, check_swap); > } > } Thanks, M. -- Without deviation from the norm, progress is not possible.