diff mbox series

[02/26] fs/proc/page.c: don't access uninitialized memmaps in fs/proc/page.c

Message ID 20191019031920.uYTou5ZN4%akpm@linux-foundation.org (mailing list archive)
State New, archived
Headers show
Series [01/26] drivers/base/memory.c: don't access uninitialized memmaps in soft_offline_page_store() | expand

Commit Message

Andrew Morton Oct. 19, 2019, 3:19 a.m. UTC 
From: David Hildenbrand <david@redhat.com>
Subject: fs/proc/page.c: don't access uninitialized memmaps in fs/proc/page.c

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.

Link: http://lkml.kernel.org/r/20191009142435.3975-2-david@redhat.com
Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online")	[visible after d0dc12e86b319]
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: Qian Cai <cai@lca.pw>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Toshiki Fukasawa <t-fukasawa@vx.jp.nec.com>
Cc: Pankaj gupta <pagupta@redhat.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Anthony Yznaga <anthony.yznaga@oracle.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: <stable@vger.kernel.org>	[4.13+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/page.c |   28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)
diff mbox series

Patch

--- a/fs/proc/page.c~mm-dont-access-uninitialized-memmaps-in-fs-proc-pagec
+++ a/fs/proc/page.c
@@ -42,10 +42,12 @@  static ssize_t kpagecount_read(struct fi
 		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
@@ -216,10 +218,11 @@  static ssize_t kpageflags_read(struct fi
 		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;
@@ -261,10 +264,11 @@  static ssize_t kpagecgroup_read(struct f
 		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);