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=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 12918C433DB for ; Thu, 11 Feb 2021 10:57:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0FCD64E2D for ; Thu, 11 Feb 2021 10:56:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229662AbhBKK4M (ORCPT ); Thu, 11 Feb 2021 05:56:12 -0500 Received: from foss.arm.com ([217.140.110.172]:49784 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230257AbhBKKxs (ORCPT ); Thu, 11 Feb 2021 05:53:48 -0500 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 7BD7E31B; Thu, 11 Feb 2021 02:52:43 -0800 (PST) Received: from [10.37.8.13] (unknown [10.37.8.13]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CE4FC3F73B; Thu, 11 Feb 2021 02:52:41 -0800 (PST) Subject: Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page To: Catalin Marinas , linux-arm-kernel@lists.infradead.org Cc: Luis Machado , Kevin Brodsky , Steven Price , stable@vger.kernel.org, Will Deacon References: <20210210180316.23654-1-catalin.marinas@arm.com> From: Vincenzo Frascino Message-ID: Date: Thu, 11 Feb 2021 10:56:46 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210210180316.23654-1-catalin.marinas@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 2/10/21 6:03 PM, Catalin Marinas wrote: > The ptrace(PTRACE_PEEKMTETAGS) implementation checks whether the user > page has valid tags (mapped with PROT_MTE) by testing the PG_mte_tagged > page flag. If this bit is cleared, ptrace(PTRACE_PEEKMTETAGS) returns > -EIO. > > A newly created (PROT_MTE) mapping points to the zero page which had its > tags zeroed during cpu_enable_mte(). If there were no prior writes to > this mapping, ptrace(PTRACE_PEEKMTETAGS) fails with -EIO since the zero > page does not have the PG_mte_tagged flag set. > > Set PG_mte_tagged on the zero page when its tags are cleared during > boot. In addition, to avoid ptrace(PTRACE_PEEKMTETAGS) succeeding on > !PROT_MTE mappings pointing to the zero page, change the > __access_remote_tags() check to (vm_flags & VM_MTE) instead of > PG_mte_tagged. > > Signed-off-by: Catalin Marinas > Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") > Cc: # 5.10.x > Cc: Will Deacon > Reported-by: Luis Machado > --- > > The fix is actually checking VM_MTE instead of PG_mte_tagged in > __access_remote_tags() but I added the WARN_ON(!PG_mte_tagged) and > setting the flag on the zero page in case we break this assumption in > the future. > > arch/arm64/kernel/cpufeature.c | 6 +----- > arch/arm64/kernel/mte.c | 3 ++- > 2 files changed, 3 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index e99eddec0a46..3e6331b64932 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1701,16 +1701,12 @@ static void bti_enable(const struct arm64_cpu_capabilities *__unused) > #ifdef CONFIG_ARM64_MTE > static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap) > { > - static bool cleared_zero_page = false; > - > /* > * Clear the tags in the zero page. This needs to be done via the > * linear map which has the Tagged attribute. > */ > - if (!cleared_zero_page) { > - cleared_zero_page = true; > + if (!test_and_set_bit(PG_mte_tagged, &ZERO_PAGE(0)->flags)) > mte_clear_page_tags(lm_alias(empty_zero_page)); > - } > > kasan_init_hw_tags_cpu(); > } > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index dc9ada64feed..80b62fe49dcf 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -329,11 +329,12 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr, > * would cause the existing tags to be cleared if the page > * was never mapped with PROT_MTE. > */ > - if (!test_bit(PG_mte_tagged, &page->flags)) { > + if (!(vma->vm_flags & VM_MTE)) { > ret = -EOPNOTSUPP; > put_page(page); > break; > } > + WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags)); > Nit: I would live a white line before WARN_ON_ONCE() to improve readability and maybe transform it in WARN_ONCE() with a message (alternatively a comment on top) based on what you are explaining in the commit message. Otherwise: Reviewed-by: Vincenzo Frascino > /* limit access to the end of the page */ > offset = offset_in_page(addr); > -- Regards, Vincenzo 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=-15.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,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 E173DC433E9 for ; Thu, 11 Feb 2021 10:55:28 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 90FF564E2D for ; Thu, 11 Feb 2021 10:55:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 90FF564E2D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com 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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=CzKr7yhC6HCaSLILqm44+iipBvF5wsEDFnDDt6LzKDM=; b=zwhjBu27T9NWkVjsHnVvZ9ZFU i1qUSYlTL9EDm/1AFczpOCrt3GtVcFIoByk3MfcfoC32CdE5Y98aOnjiA/vQLW/ndFyaswy9Z/Z6I DHkXeY2dP3/LcXijvc8lxbbC+0jZ69oLiG6SGW64dEhx/Yat1+wk4jYODapagJwx0bOvfeRUP3nSm c4PePkdLdrvrZNqXhIPMSO+xl/ko3pFyIkyebEROCMIoe3P6TZNfdjXIMcCdXf7hEWy2v4dQXXjCc nBYD5dMjc9XEb5YRpdQhbA/8HWcUm6YaJBRbCF39b8MkU5RQcDXWWzyirdst5ZhcJ5HyArqzOsCwF jAUAWY8Bw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1lA9ai-0007lu-Gn; Thu, 11 Feb 2021 10:52:56 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1lA9aY-0007iM-RS for linux-arm-kernel@lists.infradead.org; Thu, 11 Feb 2021 10:52:48 +0000 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 7BD7E31B; Thu, 11 Feb 2021 02:52:43 -0800 (PST) Received: from [10.37.8.13] (unknown [10.37.8.13]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CE4FC3F73B; Thu, 11 Feb 2021 02:52:41 -0800 (PST) Subject: Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page To: Catalin Marinas , linux-arm-kernel@lists.infradead.org References: <20210210180316.23654-1-catalin.marinas@arm.com> From: Vincenzo Frascino Message-ID: Date: Thu, 11 Feb 2021 10:56:46 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210210180316.23654-1-catalin.marinas@arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210211_055247_063623_03834C84 X-CRM114-Status: GOOD ( 30.12 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Will Deacon , Kevin Brodsky , Luis Machado , stable@vger.kernel.org, Steven Price 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 On 2/10/21 6:03 PM, Catalin Marinas wrote: > The ptrace(PTRACE_PEEKMTETAGS) implementation checks whether the user > page has valid tags (mapped with PROT_MTE) by testing the PG_mte_tagged > page flag. If this bit is cleared, ptrace(PTRACE_PEEKMTETAGS) returns > -EIO. > > A newly created (PROT_MTE) mapping points to the zero page which had its > tags zeroed during cpu_enable_mte(). If there were no prior writes to > this mapping, ptrace(PTRACE_PEEKMTETAGS) fails with -EIO since the zero > page does not have the PG_mte_tagged flag set. > > Set PG_mte_tagged on the zero page when its tags are cleared during > boot. In addition, to avoid ptrace(PTRACE_PEEKMTETAGS) succeeding on > !PROT_MTE mappings pointing to the zero page, change the > __access_remote_tags() check to (vm_flags & VM_MTE) instead of > PG_mte_tagged. > > Signed-off-by: Catalin Marinas > Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") > Cc: # 5.10.x > Cc: Will Deacon > Reported-by: Luis Machado > --- > > The fix is actually checking VM_MTE instead of PG_mte_tagged in > __access_remote_tags() but I added the WARN_ON(!PG_mte_tagged) and > setting the flag on the zero page in case we break this assumption in > the future. > > arch/arm64/kernel/cpufeature.c | 6 +----- > arch/arm64/kernel/mte.c | 3 ++- > 2 files changed, 3 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index e99eddec0a46..3e6331b64932 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1701,16 +1701,12 @@ static void bti_enable(const struct arm64_cpu_capabilities *__unused) > #ifdef CONFIG_ARM64_MTE > static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap) > { > - static bool cleared_zero_page = false; > - > /* > * Clear the tags in the zero page. This needs to be done via the > * linear map which has the Tagged attribute. > */ > - if (!cleared_zero_page) { > - cleared_zero_page = true; > + if (!test_and_set_bit(PG_mte_tagged, &ZERO_PAGE(0)->flags)) > mte_clear_page_tags(lm_alias(empty_zero_page)); > - } > > kasan_init_hw_tags_cpu(); > } > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index dc9ada64feed..80b62fe49dcf 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -329,11 +329,12 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr, > * would cause the existing tags to be cleared if the page > * was never mapped with PROT_MTE. > */ > - if (!test_bit(PG_mte_tagged, &page->flags)) { > + if (!(vma->vm_flags & VM_MTE)) { > ret = -EOPNOTSUPP; > put_page(page); > break; > } > + WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags)); > Nit: I would live a white line before WARN_ON_ONCE() to improve readability and maybe transform it in WARN_ONCE() with a message (alternatively a comment on top) based on what you are explaining in the commit message. Otherwise: Reviewed-by: Vincenzo Frascino > /* limit access to the end of the page */ > offset = offset_in_page(addr); > -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel