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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 4D9F7ECE58D for ; Wed, 9 Oct 2019 14:41:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 18F3320B7C for ; Wed, 9 Oct 2019 14:41:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570632105; bh=jc71WNpC3MZfHvf5s+XbA13mLFopbjxF2T5tg1XYETc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=fBv4T5BPAfnwJWZFvRYNCGyYPS8SUYbLP7UQ3zXDt12K9Ov0MkxV7LH7Xb7gsRwTY rENPMHPELuqEHuF9ddDjUXbr1e8YzF98HW/lo9BrfTw+24oCyATK84EABVUGgoSap+ C5axhsvDgi2rWf1tdpsyHulqbPslnC1mPKhxXXO4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731611AbfJIOln (ORCPT ); Wed, 9 Oct 2019 10:41:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:33988 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731597AbfJIOlm (ORCPT ); Wed, 9 Oct 2019 10:41:42 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id EFE1AAD12; Wed, 9 Oct 2019 14:41:38 +0000 (UTC) Date: Wed, 9 Oct 2019 16:41:37 +0200 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Qian Cai , Dan Williams , Alexey Dobriyan , Andrew Morton , Stephen Rothwell , Toshiki Fukasawa , Pankaj gupta , Mike Rapoport , Anthony Yznaga , "Aneesh Kumar K.V" , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v2 1/2] mm: Don't access uninitialized memmaps in fs/proc/page.c Message-ID: <20191009144137.GG6681@dhcp22.suse.cz> References: <20191009142435.3975-1-david@redhat.com> <20191009142435.3975-2-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191009142435.3975-2-david@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 09-10-19 16:24:34, David Hildenbrand wrote: > There are three places where we access uninitialized memmaps, namely: > - /proc/kpagecount > - /proc/kpageflags > - /proc/kpagecgroup > > 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 > > For now, let's drop support for ZONE_DEVICE from the three pseudo files > in order to fix this. To distinguish offline memory (with garbage memmap) > from ZONE_DEVICE memory with properly initialized memmaps, we would have to > check get_dev_pagemap() and pfn_zone_device_reserved() right now. The usage > of both (especially, special casing devmem) is frowned upon and needs to > be reworked. The fundamental issue we have is: > > if (pfn_to_online_page(pfn)) { > /* memmap initialized */ > } else if (pfn_valid(pfn)) { > /* > * ??? > * a) offline memory. memmap garbage. > * b) devmem: memmap initialized to ZONE_DEVICE. > * c) devmem: reserved for driver. memmap garbage. > * (d) devmem: memmap currently initializing - garbage) > */ > } > > We'll leave the pfn_zone_device_reserved() check in stable_page_flags() > in place as that function is also used from memory failure. We now > no longer dump information about pages that are not in use anymore - > offline. > > Reported-by: Qian Cai > Cc: Dan Williams > Cc: Alexey Dobriyan > Cc: Andrew Morton > Cc: Stephen Rothwell > Cc: Toshiki Fukasawa > Cc: Pankaj gupta > Cc: Mike Rapoport > Cc: Anthony Yznaga > Cc: Michal Hocko > Cc: "Aneesh Kumar K.V" > Cc: linux-fsdevel@vger.kernel.org > Signed-off-by: David Hildenbrand Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319 usage of pfn_to_online_page is the right way to dereference the pfn here. My understanding of the zone device internals is limited to see whether this fixes it as well. Acked-by: Michal Hocko > --- > fs/proc/page.c | 28 ++++++++++++++++------------ > 1 file changed, 16 insertions(+), 12 deletions(-) > > diff --git a/fs/proc/page.c b/fs/proc/page.c > index decd3fe39674..e40dbfe1168e 100644 > --- a/fs/proc/page.c > +++ b/fs/proc/page.c > @@ -42,10 +42,12 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, > return -EINVAL; > > while (count > 0) { > - if (pfn_valid(pfn)) > - ppage = pfn_to_page(pfn); > - else > - ppage = NULL; > + /* > + * TODO: ZONE_DEVICE support requires to identify > + * memmaps that were actually initialized. > + */ > + ppage = pfn_to_online_page(pfn); > + > if (!ppage || PageSlab(ppage) || page_has_type(ppage)) > pcount = 0; > else > @@ -218,10 +220,11 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf, > return -EINVAL; > > while (count > 0) { > - if (pfn_valid(pfn)) > - ppage = pfn_to_page(pfn); > - else > - ppage = NULL; > + /* > + * TODO: ZONE_DEVICE support requires to identify > + * memmaps that were actually initialized. > + */ > + ppage = pfn_to_online_page(pfn); > > if (put_user(stable_page_flags(ppage), out)) { > ret = -EFAULT; > @@ -263,10 +266,11 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf, > return -EINVAL; > > while (count > 0) { > - if (pfn_valid(pfn)) > - ppage = pfn_to_page(pfn); > - else > - ppage = NULL; > + /* > + * TODO: ZONE_DEVICE support requires to identify > + * memmaps that were actually initialized. > + */ > + ppage = pfn_to_online_page(pfn); > > if (ppage) > ino = page_cgroup_ino(ppage); > -- > 2.21.0 -- Michal Hocko SUSE Labs