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=-16.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2C25EC43460 for ; Sun, 2 May 2021 06:33:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 08F5561481 for ; Sun, 2 May 2021 06:33:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231529AbhEBGds (ORCPT ); Sun, 2 May 2021 02:33:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:60206 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229526AbhEBGds (ORCPT ); Sun, 2 May 2021 02:33:48 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 584A561466; Sun, 2 May 2021 06:32:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1619937177; bh=AamYV1zarM8XROObHow2GS9jtvK08e2YVaUvh7HsmvE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hfsCipSZ7Oat5Tih3ZX2Yr+KpqdTvvfdz3DnLfEWTQ+gdClichLYDIqAOtHuQ2ui/ Qm+PFOgyT8fEktmjbMUHa7UsJRxbTIUzMy7lJUA3ncrBKcZXW2P09S2aEMI6JXVt85 U7q5MJ5XHq2LtHOIQLvXIHTNPzFrUN+cIRZGdSiWyumhz5ZYq5ubze/C9xO8DIYOaU m9LVPv64fB7BQTYpJAZetDfAwBE5jznlNPm2E/4eCwILYszSpc6Fu7OIXd0hQDttLE 3yhzXWA7/Js/s9lT31k/6SVQNDlkRE4KDsF13L9LBfRG6tXxZ0KQUbFVVe/hirZA6t aFCUY99Y42pqA== Date: Sun, 2 May 2021 09:32:46 +0300 From: Mike Rapoport To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Andrew Morton , "Michael S. Tsirkin" , Jason Wang , Alexey Dobriyan , "Matthew Wilcox (Oracle)" , Oscar Salvador , Michal Hocko , Roman Gushchin , Alex Shi , Steven Price , Mike Kravetz , Aili Yao , Jiri Bohac , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Naoya Horiguchi , linux-hyperv@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v1 4/7] fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages Message-ID: References: <20210429122519.15183-1-david@redhat.com> <20210429122519.15183-5-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210429122519.15183-5-david@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Apr 29, 2021 at 02:25:16PM +0200, David Hildenbrand wrote: > Let's avoid reading: > > 1) Offline memory sections: the content of offline memory sections is stale > as the memory is effectively unused by the kernel. On s390x with standby > memory, offline memory sections (belonging to offline storage > increments) are not accessible. With virtio-mem and the hyper-v balloon, > we can have unavailable memory chunks that should not be accessed inside > offline memory sections. Last but not least, offline memory sections > might contain hwpoisoned pages which we can no longer identify > because the memmap is stale. > > 2) PG_offline pages: logically offline pages that are documented as > "The content of these pages is effectively stale. Such pages should not > be touched (read/write/dump/save) except by their owner.". > Examples include pages inflated in a balloon or unavailble memory > ranges inside hotplugged memory sections with virtio-mem or the hyper-v > balloon. > > 3) PG_hwpoison pages: Reading pages marked as hwpoisoned can be fatal. > As documented: "Accessing is not safe since it may cause another machine > check. Don't touch!" > > Reading /proc/kcore now performs similar checks as when reading > /proc/vmcore for kdump via makedumpfile: problematic pages are exclude. > It's also similar to hibernation code, however, we don't skip hwpoisoned > pages when processing pages in kernel/power/snapshot.c:saveable_page() yet. > > Note 1: we can race against memory offlining code, especially > memory going offline and getting unplugged: however, we will properly tear > down the identity mapping and handle faults gracefully when accessing > this memory from kcore code. > > Note 2: we can race against drivers setting PageOffline() and turning > memory inaccessible in the hypervisor. We'll handle this in a follow-up > patch. > > Signed-off-by: David Hildenbrand Reviewed-by: Mike Rapoport > --- > fs/proc/kcore.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > index ed6fbb3bd50c..92ff1e4436cb 100644 > --- a/fs/proc/kcore.c > +++ b/fs/proc/kcore.c > @@ -465,6 +465,9 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > m = NULL; > while (buflen) { > + struct page *page; > + unsigned long pfn; > + > /* > * If this is the first iteration or the address is not within > * the previous entry, search for a matching entry. > @@ -503,7 +506,16 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > } > break; > case KCORE_RAM: > - if (!pfn_is_ram(__pa(start) >> PAGE_SHIFT)) { > + pfn = __pa(start) >> PAGE_SHIFT; > + page = pfn_to_online_page(pfn); > + > + /* > + * Don't read offline sections, logically offline pages > + * (e.g., inflated in a balloon), hwpoisoned pages, > + * and explicitly excluded physical ranges. > + */ > + if (!page || PageOffline(page) || > + is_page_hwpoison(page) || !pfn_is_ram(pfn)) { > if (clear_user(buffer, tsz)) { > ret = -EFAULT; > goto out; > -- > 2.30.2 > -- Sincerely yours, Mike.