From nobody Mon Feb 9 21:12:28 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=arm.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1623661793701225.52981148307288; Mon, 14 Jun 2021 02:09:53 -0700 (PDT) Received: from localhost ([::1]:38802 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lsibQ-0001HU-JS for importer@patchew.org; Mon, 14 Jun 2021 05:09:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50620) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lsiXU-0000y8-Du for qemu-devel@nongnu.org; Mon, 14 Jun 2021 05:05:48 -0400 Received: from foss.arm.com ([217.140.110.172]:50886) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lsiXQ-0005mw-ME for qemu-devel@nongnu.org; Mon, 14 Jun 2021 05:05:48 -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 CA644113E; Mon, 14 Jun 2021 02:05:43 -0700 (PDT) Received: from e112269-lin.arm.com (autoplooker.cambridge.arm.com [10.1.194.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0A8A33F694; Mon, 14 Jun 2021 02:05:40 -0700 (PDT) From: Steven Price To: Catalin Marinas , Marc Zyngier , Will Deacon Subject: [PATCH v15 1/7] arm64: mte: Handle race when synchronising tags Date: Mon, 14 Jun 2021 10:05:19 +0100 Message-Id: <20210614090525.4338-2-steven.price@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210614090525.4338-1-steven.price@arm.com> References: <20210614090525.4338-1-steven.price@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=217.140.110.172; envelope-from=steven.price@arm.com; helo=foss.arm.com 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, Dave Martin , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Steven Price , James Morse , Julien Thierry , Thomas Gleixner , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" 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 u= ser-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; =20 static bool report_fault_once =3D true; +static DEFINE_SPINLOCK(tag_sync_lock); =20 #ifdef CONFIG_KASAN_HW_TAGS /* Whether the MTE asynchronous mode is enabled. */ @@ -34,13 +35,22 @@ EXPORT_SYMBOL_GPL(mte_async_mode); =20 static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_= swap) { + unsigned long flags; pte_t old_pte =3D READ_ONCE(*ptep); =20 + 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 =3D pte_to_swp_entry(old_pte); =20 - 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; + } } =20 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); } =20 void mte_sync_tags(pte_t *ptep, pte_t pte) @@ -63,7 +77,7 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) =20 /* if PG_mte_tagged is set, tags have already been initialised */ for (i =3D 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); } } --=20 2.20.1