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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 D89FFC3A5A3 for ; Sun, 25 Aug 2019 16:38:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B133C2082F for ; Sun, 25 Aug 2019 16:38:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728511AbfHYQig (ORCPT ); Sun, 25 Aug 2019 12:38:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47016 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726182AbfHYQif (ORCPT ); Sun, 25 Aug 2019 12:38:35 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2ECD437E79; Sun, 25 Aug 2019 16:38:35 +0000 (UTC) Received: from llong.com (ovpn-120-143.rdu2.redhat.com [10.10.120.143]) by smtp.corp.redhat.com (Postfix) with ESMTP id 37A4F1001958; Sun, 25 Aug 2019 16:38:27 +0000 (UTC) From: Waiman Long To: Alexey Dobriyan , Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Stephen Rothwell , "Michael S. Tsirkin" , Waiman Long Subject: [PATCH] fs/proc/page: Skip uninitialized page when iterating page structures Date: Sun, 25 Aug 2019 12:38:05 -0400 Message-Id: <20190825163805.3036-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Sun, 25 Aug 2019 16:38:35 +0000 (UTC) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org It was found that on a dual-socket x86-64 system with nvdimm, reading /proc/kpagecount may cause the system to panic: =================== [ 79.917682] BUG: unable to handle page fault for address: fffffffffffffffe [ 79.924558] #PF: supervisor read access in kernel mode [ 79.929696] #PF: error_code(0x0000) - not-present page [ 79.934834] PGD 87b60d067 P4D 87b60d067 PUD 87b60f067 PMD 0 [ 79.940494] Oops: 0000 [#1] SMP NOPTI [ 79.944157] CPU: 89 PID: 3455 Comm: cp Not tainted 5.3.0-rc5-test+ #14 [ 79.950682] Hardware name: Dell Inc. PowerEdge R740/07X9K0, BIOS 2.2.11 06/13/2019 [ 79.958246] RIP: 0010:kpagecount_read+0xdb/0x1a0 [ 79.962859] Code: e8 09 83 e0 3f 48 0f a3 02 73 2d 4c 89 f7 48 c1 e7 06 48 03 3d fe da de 00 74 1d 48 8b 57 08 48 8d 42 ff 83 e2 01 48 0f 44 c7 <48> 8b 00 f6 c4 02 75 06 83 7f 30 80 7d 62 31 c0 4c 89 f9 e8 5d c9 [ 79.981603] RSP: 0018:ffffb0d9c950fe70 EFLAGS: 00010202 [ 79.986830] RAX: fffffffffffffffe RBX: ffff8beebe5383c0 RCX: ffffb0d9c950ff00 [ 79.993963] RDX: 0000000000000001 RSI: 00007fd85b29e000 RDI: ffffe77a22000000 [ 80.001095] RBP: 0000000000020000 R08: 0000000000000001 R09: 0000000000000000 [ 80.008226] R10: 0000000000000000 R11: 0000000000000001 R12: 00007fd85b29e000 [ 80.015358] R13: ffffffff893f0480 R14: 0000000000880000 R15: 00007fd85b29e000 [ 80.022491] FS: 00007fd85b312800(0000) GS:ffff8c359fb00000(0000) knlGS:0000000000000000 [ 80.030576] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 80.036321] CR2: fffffffffffffffe CR3: 0000004f54a38001 CR4: 00000000007606e0 [ 80.043455] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 80.050586] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 80.057718] PKRU: 55555554 [ 80.060428] Call Trace: [ 80.062877] proc_reg_read+0x39/0x60 [ 80.066459] vfs_read+0x91/0x140 [ 80.069686] ksys_read+0x59/0xd0 [ 80.072922] do_syscall_64+0x59/0x1e0 [ 80.076588] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 80.081637] RIP: 0033:0x7fd85a7f5d75 =================== It turns out the panic was caused by the kpagecount_read() function hitting an uninitialized page structure at PFN 0x880000 where all its fields were set to -1. The compound_head value of -1 will mislead the kernel to treat -2 as a pointer to the head page of the compound page leading to the crash. The system have 12 GB of nvdimm ranging from PFN 0x880000-0xb7ffff. However, only PFN 0x88c200-0xb7ffff are released by the nvdimm driver to the kernel and initialized. IOW, PFN 0x880000-0x88c1ff remain uninitialized. Perhaps these 196 MB of nvdimm are reserved for internal use. To fix the panic, we need to find out if a page structure has been initialized. This is done now by checking if the PFN is in the range of a memory zone assuming that pages in a zone is either correctly marked as not present in the mem_section structure or have their page structures initialized. Signed-off-by: Waiman Long --- fs/proc/page.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 65 insertions(+), 3 deletions(-) diff --git a/fs/proc/page.c b/fs/proc/page.c index 544d1ee15aee..ef697eb42065 100644 --- a/fs/proc/page.c +++ b/fs/proc/page.c @@ -21,6 +21,64 @@ #define KPMMASK (KPMSIZE - 1) #define KPMBITS (KPMSIZE * BITS_PER_BYTE) +/* + * It is possible a page structure is contained in a mem_section that is + * regarded as valid but the page structure itself is not properly + * initialized. For example, portion of the device memory may be used + * internally by device driver or firmware without being managed by the + * kernel and hence their page structures may not be initialized. + * + * An uninitialized page structure may cause the PFN iteration code + * in this file to panic the system. To safe-guard against this + * possibility, an additional check of the PFN is done to make sure + * that it is in a valid range in one of the memory zones: + * + * [zone_start_pfn, zone_start_pfn + spanned_pages) + * + * It is possible that some of the PFNs within a zone is not present. + * In this case, it will have to rely on the current mem_section check + * as well as the affected page structures are still properly initialized. + */ +struct zone_range { + unsigned long pfn_start; + unsigned long pfn_end; +}; + +static void find_next_zone_range(struct zone_range *range) +{ + unsigned long start, end; + pg_data_t *pgdat; + struct zone *zone; + int i; + + /* + * Scan all the zone structures to find the next closest one. + */ + start = end = -1UL + for (pgdat = first_online_pgdat(); pgdat; + pgdat = next_online_pgdat(pgdat)) { + for (zone = pgdat->node_zones, i = 0; i < MAX_NR_ZONES; + zone++, i++) { + if (!zone->spanned_pages) + continue; + if ((zone->zone_start_pfn >= range->pfn_end) && + (zone->zone_start_pfn < start)) { + start = zone->zone_start_pfn; + end = start + zone->spanned_pages; + } + } + } + range->pfn_start = start; + range->pfn_end = end; +} + +static inline bool pfn_in_zone(unsigned long pfn, struct zone_range *range) +{ + if (pfn >= range->pfn_end) + find_next_zone_range(range); + return pfn >= range->start && pfn < range->end; +} + /* /proc/kpagecount - an array exposing page counts * * Each entry is a u64 representing the corresponding @@ -31,6 +89,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, { u64 __user *out = (u64 __user *)buf; struct page *ppage; + struct zone_range range = { 0, 0 }; unsigned long src = *ppos; unsigned long pfn; ssize_t ret = 0; @@ -42,10 +101,11 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, return -EINVAL; while (count > 0) { - if (pfn_valid(pfn)) + if (pfn_valid(pfn) && pfn_in_zone(pfn, &range)) ppage = pfn_to_page(pfn); else ppage = NULL; + if (!ppage || PageSlab(ppage) || page_has_type(ppage)) pcount = 0; else @@ -206,6 +266,7 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf, { u64 __user *out = (u64 __user *)buf; struct page *ppage; + struct zone_range range = { 0, 0 }; unsigned long src = *ppos; unsigned long pfn; ssize_t ret = 0; @@ -216,7 +277,7 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf, return -EINVAL; while (count > 0) { - if (pfn_valid(pfn)) + if (pfn_valid(pfn) && pfn_in_zone(pfn, &range)) ppage = pfn_to_page(pfn); else ppage = NULL; @@ -250,6 +311,7 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf, { u64 __user *out = (u64 __user *)buf; struct page *ppage; + struct zone_range range = { 0, 0 }; unsigned long src = *ppos; unsigned long pfn; ssize_t ret = 0; @@ -261,7 +323,7 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf, return -EINVAL; while (count > 0) { - if (pfn_valid(pfn)) + if (pfn_valid(pfn) && pfn_in_zone(pfn, &range)) ppage = pfn_to_page(pfn); else ppage = NULL; -- 2.18.1