From patchwork Wed Oct 9 14:24:34 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 11181283 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 62E891668 for ; Wed, 9 Oct 2019 14:24:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 458F021A4A for ; Wed, 9 Oct 2019 14:24:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731454AbfJIOYr (ORCPT ); Wed, 9 Oct 2019 10:24:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38608 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729491AbfJIOYr (ORCPT ); Wed, 9 Oct 2019 10:24:47 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6047481DF1; Wed, 9 Oct 2019 14:24:46 +0000 (UTC) Received: from t460s.redhat.com (unknown [10.36.118.16]) by smtp.corp.redhat.com (Postfix) with ESMTP id 14C6460BF4; Wed, 9 Oct 2019 14:24:42 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, David Hildenbrand , Qian Cai , Dan Williams , Alexey Dobriyan , Andrew Morton , Stephen Rothwell , Toshiki Fukasawa , Pankaj gupta , Mike Rapoport , Anthony Yznaga , Michal Hocko , "Aneesh Kumar K.V" , linux-fsdevel@vger.kernel.org Subject: [PATCH v2 1/2] mm: Don't access uninitialized memmaps in fs/proc/page.c Date: Wed, 9 Oct 2019 16:24:34 +0200 Message-Id: <20191009142435.3975-2-david@redhat.com> In-Reply-To: <20191009142435.3975-1-david@redhat.com> References: <20191009142435.3975-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Wed, 09 Oct 2019 14:24:46 +0000 (UTC) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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 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);