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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 651C7ECE58C for ; Fri, 11 Oct 2019 09:54:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 34ED220679 for ; Fri, 11 Oct 2019 09:54:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727695AbfJKJyD (ORCPT ); Fri, 11 Oct 2019 05:54:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50948 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726585AbfJKJyD (ORCPT ); Fri, 11 Oct 2019 05:54:03 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5D19618C8902; Fri, 11 Oct 2019 09:54:02 +0000 (UTC) Received: from [10.36.118.168] (unknown [10.36.118.168]) by smtp.corp.redhat.com (Postfix) with ESMTP id 84D1A6092F; Fri, 11 Oct 2019 09:53:58 +0000 (UTC) Subject: Re: [PATCH v1] mm: Fix access of uninitialized memmaps in fs/proc/page.c To: Naoya Horiguchi Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Qian Cai , Alexey Dobriyan , Andrew Morton , Stephen Rothwell , Michal Hocko , Toshiki Fukasawa , Konstantin Khlebnikov , Mike Rapoport , Anthony Yznaga , Jason Gunthorpe , Dan Williams , Logan Gunthorpe , Ira Weiny , "Aneesh Kumar K.V" , "linux-fsdevel@vger.kernel.org" References: <20191009091205.11753-1-david@redhat.com> <20191009095721.GC20971@hori.linux.bs1.fc.nec.co.jp> <20191011001124.GA17127@hori.linux.bs1.fc.nec.co.jp> <20191011005042.GB18881@hori.linux.bs1.fc.nec.co.jp> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <21d97a65-aa66-75ee-9c63-b5a3dad13b43@redhat.com> Date: Fri, 11 Oct 2019 11:53:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <20191011005042.GB18881@hori.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset=iso-2022-jp; format=flowed; delsp=yes Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.70]); Fri, 11 Oct 2019 09:54:02 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11.10.19 02:50, Naoya Horiguchi wrote: > On Fri, Oct 11, 2019 at 12:11:25AM +0000, Horiguchi Naoya(堀口 直也) wrote: >> On Thu, Oct 10, 2019 at 09:30:01AM +0200, David Hildenbrand wrote: >>> On 09.10.19 11:57, Naoya Horiguchi wrote: >>>> Hi David, >>>> >>>> On Wed, Oct 09, 2019 at 11:12:04AM +0200, David Hildenbrand wrote: >>>>> There are various places where we access uninitialized memmaps, namely: >>>>> - /proc/kpagecount >>>>> - /proc/kpageflags >>>>> - /proc/kpagecgroup >>>>> - memory_failure() - which reuses stable_page_flags() from fs/proc/page.c >>>> >>>> Ah right, memory_failure is another victim of this bug. >>>> >>>>> >>>>> We have initialized memmaps either when the section is online or when >>>>> the page was initialized to the ZONE_DEVICE. Uninitialized memmaps contain >>>>> garbage and in the worst case trigger kernel BUGs, especially with >>>>> CONFIG_PAGE_POISONING. >>>>> >>>>> For example, not onlining a DIMM during boot and calling /proc/kpagecount >>>>> with CONFIG_PAGE_POISONING: >>>>> :/# cat /proc/kpagecount > tmp.test >>>>> [ 95.600592] BUG: unable to handle page fault for address: fffffffffffffffe >>>>> [ 95.601238] #PF: supervisor read access in kernel mode >>>>> [ 95.601675] #PF: error_code(0x0000) - not-present page >>>>> [ 95.602116] PGD 114616067 P4D 114616067 PUD 114618067 PMD 0 >>>>> [ 95.602596] Oops: 0000 [#1] SMP NOPTI >>>>> [ 95.602920] CPU: 0 PID: 469 Comm: cat Not tainted 5.4.0-rc1-next-20191004+ #11 >>>>> [ 95.603547] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 >>>>> [ 95.604521] RIP: 0010:kpagecount_read+0xce/0x1e0 >>>>> [ 95.604917] Code: e8 09 83 e0 3f 48 0f a3 02 73 2d 4c 89 e7 48 c1 e7 06 48 03 3d ab 51 01 01 74 1d 48 8b 57 08 480 >>>>> [ 95.606450] RSP: 0018:ffffa14e409b7e78 EFLAGS: 00010202 >>>>> [ 95.606904] RAX: fffffffffffffffe RBX: 0000000000020000 RCX: 0000000000000000 >>>>> [ 95.607519] RDX: 0000000000000001 RSI: 00007f76b5595000 RDI: fffff35645000000 >>>>> [ 95.608128] RBP: 00007f76b5595000 R08: 0000000000000001 R09: 0000000000000000 >>>>> [ 95.608731] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000 >>>>> [ 95.609327] R13: 0000000000020000 R14: 00007f76b5595000 R15: ffffa14e409b7f08 >>>>> [ 95.609924] FS: 00007f76b577d580(0000) GS:ffff8f41bd400000(0000) knlGS:0000000000000000 >>>>> [ 95.610599] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>>> [ 95.611083] CR2: fffffffffffffffe CR3: 0000000078960000 CR4: 00000000000006f0 >>>>> [ 95.611686] Call Trace: >>>>> [ 95.611906] proc_reg_read+0x3c/0x60 >>>>> [ 95.612228] vfs_read+0xc5/0x180 >>>>> [ 95.612505] ksys_read+0x68/0xe0 >>>>> [ 95.612785] do_syscall_64+0x5c/0xa0 >>>>> [ 95.613092] entry_SYSCALL_64_after_hwframe+0x49/0xbe >>>>> >>>>> Note that there are still two possible races as far as I can see: >>>>> - pfn_to_online_page() succeeding but the memory getting offlined and >>>>> removed. get_online_mems() could help once we run into this. >>>>> - pfn_zone_device() succeeding but the memmap not being fully >>>>> initialized yet. As the memmap is initialized outside of the memory >>>>> hoptlug lock, get_online_mems() can't help. >>>>> >>>>> Let's keep the existing interfaces working with ZONE_DEVICE memory. We >>>>> can later come back and fix these rare races and eventually speed-up the >>>>> ZONE_DEVICE detection. >>>> >>>> Actually, Toshiki is writing code to refactor and optimize the pfn walking >>>> part, where we find the pfn ranges covered by zone devices by running over >>>> xarray pgmap_array and use the range info to reduce pointer dereferences >>>> to speed up pfn walk. I hope he will share it soon. >>> >>> AFAIKT, Michal is not a friend of special-casing PFN walkers in that >>> way. We should have a mechanism to detect if a memmap was initialized >>> without having to go via pgmap, special-casing. See my other mail where >>> I draft one basic approach. >> >> OK, so considering your v2 approach, we could have another pfn_to_page() >> variant like pfn_to_zone_device_page(), where we check that a given pfn >> belongs to the memory section backed by zone memory, then another check if >> the pfn has initialized memmap or not, and return NULL if memmap not >> initialied. We'll try this approach then, but if you find problems/concerns, >> please let me know. > > Sorry, you already mentioned detail here, > https://lore.kernel.org/lkml/c6198acd-8ff7-c40c-cb4e-f0f12f841b38@redhat.com/ > I'm planning on sending a proper writeup of the overall approach and pitfalls maybe next week. Feel free to ping me in case I forget. -- Thanks, David / dhildenb