From patchwork Mon May 17 12:32:32 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Price X-Patchwork-Id: 12261789 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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 370A4C433B4 for ; Mon, 17 May 2021 12:36:33 +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 EA47B61029 for ; Mon, 17 May 2021 12:36:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EA47B61029 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:47246 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1licU2-0005Sa-HC for qemu-devel@archiver.kernel.org; Mon, 17 May 2021 08:36:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54028) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1licQu-0006a7-7P for qemu-devel@nongnu.org; Mon, 17 May 2021 08:33:16 -0400 Received: from foss.arm.com ([217.140.110.172]:42718) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1licQr-0007mL-Th for qemu-devel@nongnu.org; Mon, 17 May 2021 08:33:15 -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 9433512FC; Mon, 17 May 2021 05:33:12 -0700 (PDT) Received: from e112269-lin.arm.com (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 057743F73B; Mon, 17 May 2021 05:33:08 -0700 (PDT) From: Steven Price To: Catalin Marinas , Marc Zyngier , Will Deacon Subject: [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags Date: Mon, 17 May 2021 13:32:32 +0100 Message-Id: <20210517123239.8025-2-steven.price@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210517123239.8025-1-steven.price@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> MIME-Version: 1.0 Received-SPF: pass client-ip=217.140.110.172; envelope-from=steven.price@arm.com; helo=foss.arm.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 Reviewed-by: Catalin Marinas --- --- 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; #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); } }