From patchwork Fri May 14 17:22:44 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 12258445 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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,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 5669FC43460 for ; Fri, 14 May 2021 17:23:43 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 02D6A61177 for ; Fri, 14 May 2021 17:23:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 02D6A61177 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9C5758E0001; Fri, 14 May 2021 13:23:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 99BEE6B0071; Fri, 14 May 2021 13:23:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 81D1F8E0001; Fri, 14 May 2021 13:23:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0080.hostedemail.com [216.40.44.80]) by kanga.kvack.org (Postfix) with ESMTP id 4DCD66B0070 for ; Fri, 14 May 2021 13:23:42 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E8493BEF0 for ; Fri, 14 May 2021 17:23:41 +0000 (UTC) X-FDA: 78140508642.07.D1B0496 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf21.hostedemail.com (Postfix) with ESMTP id 8B85FE0001B2 for ; Fri, 14 May 2021 17:23:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1621013021; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JA+PCClAmI2hyPxGFUfyhxo4lFjoE4jDjkNgRG+Z0Zg=; b=OvIicmqrhJ4lKzmoyhH+qRtXpIqxDbVSfHxNrm3Zd8ACL3yYWmDkee21QR6UGI7Ik1n3UI aEh1Bn6kPsymDvXjkInZygO7BbeGfrVtKo9XLe7OO6qfx5/BDzGYwhbnox5U/fb6D1wsLf +jd7Wz3wqqpuJdYm/RbLzrzy0mnzGQ4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-331-mdTs41BmMbCEVUFq-BpX9A-1; Fri, 14 May 2021 13:23:39 -0400 X-MC-Unique: mdTs41BmMbCEVUFq-BpX9A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 01F25801817; Fri, 14 May 2021 17:23:36 +0000 (UTC) Received: from t480s.redhat.com (ovpn-114-113.ams2.redhat.com [10.36.114.113]) by smtp.corp.redhat.com (Postfix) with ESMTP id E98111A86D; Fri, 14 May 2021 17:23:26 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: David Hildenbrand , Andrew Morton , "Michael S. Tsirkin" , Jason Wang , Alexey Dobriyan , Mike Rapoport , "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, Mike Rapoport Subject: [PATCH v2 3/6] fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages Date: Fri, 14 May 2021 19:22:44 +0200 Message-Id: <20210514172247.176750-4-david@redhat.com> In-Reply-To: <20210514172247.176750-1-david@redhat.com> References: <20210514172247.176750-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Rspamd-Queue-Id: 8B85FE0001B2 Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OvIicmqr; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf21.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com X-Rspamd-Server: rspam03 X-Stat-Signature: e6ficz8e59xto6uzim5epiihega83i3s X-HE-Tag: 1621013021-748284 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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!" Introduce is_page_hwpoison(), adding a comment that it is inherently racy but best we can really do. 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. Reviewed-by: Mike Rapoport Signed-off-by: David Hildenbrand Reviewed-by: Oscar Salvador --- fs/proc/kcore.c | 14 +++++++++++++- include/linux/page-flags.h | 12 ++++++++++++ 2 files changed, 25 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; diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 04a34c08e0a6..daed82744f4b 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -694,6 +694,18 @@ PAGEFLAG_FALSE(DoubleMap) TESTSCFLAG_FALSE(DoubleMap) #endif +/* + * Check if a page is currently marked HWPoisoned. Note that this check is + * best effort only and inherently racy: there is no way to synchronize with + * failing hardware. + */ +static inline bool is_page_hwpoison(struct page *page) +{ + if (PageHWPoison(page)) + return true; + return PageHuge(page) && PageHWPoison(compound_head(page)); +} + /* * For pages that are never mapped to userspace (and aren't PageSlab), * page_type may be used. Because it is initialised to -1, we invert the