[PATCH 4.9 021/218] mm/pages_alloc.c: dont create ZONE_MOVABLE beyond the end of a node

Greg Kroah-Hartman
2022-04-18T14:08:47Z

From: Alistair Popple <apopple@nvidia.com>

commit ddbc84f3f595cf1fc8234a191193b5d20ad43938 upstream.

ZONE_MOVABLE uses the remaining memory in each node. Its starting pfn
is also aligned to MAX_ORDER_NR_PAGES. It is possible for the remaining
memory in a node to be less than MAX_ORDER_NR_PAGES, meaning there is
not enough room for ZONE_MOVABLE on that node.

Unfortunately this condition is not checked for. This leads to
zone_movable_pfn[] getting set to a pfn greater than the last pfn in a
node.

calculate_node_totalpages() then sets zone->present_pages to be greater
than zone->spanned_pages which is invalid, as spanned_pages represents
the maximum number of pages in a zone assuming no holes.

Subsequently it is possible free_area_init_core() will observe a zone of
size zero with present pages. In this case it will skip setting up the
zone, including the initialisation of free_lists[].

However populated_zone() checks zone->present_pages to see if a zone has
memory available. This is used by iterators such as
walk_zones_in_node(). pagetypeinfo_showfree() uses this to walk the
free_list of each zone in each node, which are assumed to be initialised
due to the zone not being empty.

As free_area_init_core() never initialised the free_lists[] this results
in the following kernel crash when trying to read /proc/pagetypeinfo:

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI
CPU: 0 PID: 456 Comm: cat Not tainted 5.16.0 #461
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
RIP: 0010:pagetypeinfo_show+0x163/0x460
Code: 9e 82 e8 80 57 0e 00 49 8b 06 b9 01 00 00 00 4c 39 f0 75 16 e9 65 02 00 00 48 83 c1 01 48 81 f9 a0 86 01 00 0f 84 48 02 00 00 <48> 8b 00 4c 39 f0 75 e7 48 c7 c2 80 a2 e2 82 48 c7 c6 79 ef e3 82
RSP: 0018:ffffc90001c4bd10 EFLAGS: 00010003
RAX: 0000000000000000 RBX: ffff88801105f638 RCX: 0000000000000001
RDX: 0000000000000001 RSI: 000000000000068b RDI: ffff8880163dc68b
RBP: ffffc90001c4bd90 R08: 0000000000000001 R09: ffff8880163dc67e
R10: 656c6261766f6d6e R11: 6c6261766f6d6e55 R12: ffff88807ffb4a00
R13: ffff88807ffb49f8 R14: ffff88807ffb4580 R15: ffff88807ffb3000
FS: 00007f9c83eff5c0(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000013c8e000 CR4: 0000000000350ef0
Call Trace:
seq_read_iter+0x128/0x460
proc_reg_read_iter+0x51/0x80
new_sync_read+0x113/0x1a0
vfs_read+0x136/0x1d0
ksys_read+0x70/0xf0
__x64_sys_read+0x1a/0x20
do_syscall_64+0x3b/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix this by checking that the aligned zone_movable_pfn[] does not exceed
the end of the node, and if it does skip creating a movable zone on this
node.

Link: https://lkml.kernel.org/r/20220215025831.2113067-1-apopple@nvidia.com
Fixes: 2a1e274acf0b ("Create the ZONE_MOVABLE zone")
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/page_alloc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6267,10 +6267,17 @@ restart:

out2:
/* Align start of ZONE_MOVABLE on all nids to MAX_ORDER_NR_PAGES */
- for (nid = 0; nid < MAX_NUMNODES; nid++)
+ for (nid = 0; nid < MAX_NUMNODES; nid++) {
+ unsigned long start_pfn, end_pfn;
+
zone_movable_pfn[nid] =
roundup(zone_movable_pfn[nid], MAX_ORDER_NR_PAGES);

+ get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
+ if (zone_movable_pfn[nid] >= end_pfn)
+ zone_movable_pfn[nid] = 0;
+ }
+
out:
/* restore the node_state */
node_states[N_MEMORY] = saved_node_state;