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=-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 44F68C2B9F7 for ; Wed, 26 May 2021 09:32:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E69DF613D6 for ; Wed, 26 May 2021 09:32:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E69DF613D6 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 8D6E26B0074; Wed, 26 May 2021 05:32:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8850F6B0075; Wed, 26 May 2021 05:32:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6D7896B0078; Wed, 26 May 2021 05:32:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0102.hostedemail.com [216.40.44.102]) by kanga.kvack.org (Postfix) with ESMTP id 388AD6B0074 for ; Wed, 26 May 2021 05:32:09 -0400 (EDT) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id D1470181AF5C4 for ; Wed, 26 May 2021 09:32:08 +0000 (UTC) X-FDA: 78182865936.13.BFB1BF3 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf23.hostedemail.com (Postfix) with ESMTP id 984BCA0001CB for ; Wed, 26 May 2021 09:32:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622021528; 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=HpQl70FCJrKzkRws/ycp8B14QnuETKoEKh3YFLooSpk=; b=gqiObnwYZBPS9mVSMmPBvXlbdA/lVJynS9Kl15KUOiCLT9XWSndR7bDmW9krIqLejnBxjL hDErOrWJrRSo0Nb/74Iimiox0jl8LP6C0fCtPQossoFesT7O1zVjHbOV4MZjmxIFyauL4Q oycehSI7QW88FB6R4T+F92hRnSqe7So= 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-273-bVRoSnEGNimMg5ofHHzOIg-1; Wed, 26 May 2021 05:31:26 -0400 X-MC-Unique: bVRoSnEGNimMg5ofHHzOIg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2C4F0106BB2B; Wed, 26 May 2021 09:31:23 +0000 (UTC) Received: from t480s.redhat.com (ovpn-113-99.ams2.redhat.com [10.36.113.99]) by smtp.corp.redhat.com (Postfix) with ESMTP id 668435D9CC; Wed, 26 May 2021 09:31:17 +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 v3 3/6] fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages Date: Wed, 26 May 2021 11:30:38 +0200 Message-Id: <20210526093041.8800-4-david@redhat.com> In-Reply-To: <20210526093041.8800-1-david@redhat.com> References: <20210526093041.8800-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Rspamd-Queue-Id: 984BCA0001CB Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=gqiObnwY; spf=none (imf23.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam04 X-Stat-Signature: cgdpgpf79mq6cb5nj9txiqz1qyzztuic X-HE-Tag: 1622021522-617335 Content-Transfer-Encoding: quoted-printable 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 sta= le as the memory is effectively unused by the kernel. On s390x with stand= by memory, offline memory sections (belonging to offline storage increments) are not accessible. With virtio-mem and the hyper-v balloo= n, we can have unavailable memory chunks that should not be accessed insi= de 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 no= t 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 machi= ne 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() ye= t. Note 1: we can race against memory offlining code, especially memory going offline and getting unplugged: however, we will properly tea= r 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 Reviewed-by: Oscar Salvador Signed-off-by: David Hildenbrand --- 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, si= ze_t buflen, loff_t *fpos) =20 m =3D 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, s= ize_t buflen, loff_t *fpos) } break; case KCORE_RAM: - if (!pfn_is_ram(__pa(start) >> PAGE_SHIFT)) { + pfn =3D __pa(start) >> PAGE_SHIFT; + page =3D 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 =3D -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 =20 +/* + * 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 th= e --=20 2.31.1