Commit a26ee565 authored Oct 18, 2019 by Qian Cai Committed by Linus Torvalds Oct 19, 2019

mm/page_owner: don't access uninitialized memmaps when reading /proc/pagetypeinfo

Uninitialized memmaps contain garbage and in the worst case trigger
kernel BUGs, especially with CONFIG_PAGE_POISONING.  They should not get
touched.

For example, when not onlining a memory block that is spanned by a zone
and reading /proc/pagetypeinfo with CONFIG_DEBUG_VM_PGFLAGS and
CONFIG_PAGE_POISONING, we can trigger a kernel BUG:

  :/# echo 1 > /sys/devices/system/memory/memory40/online
  :/# echo 1 > /sys/devices/system/memory/memory42/online
  :/# cat /proc/pagetypeinfo > test.file
   page:fffff2c585200000 is uninitialized and poisoned
   raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
   raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
   page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
   There is not page extension available.
   ------------[ cut here ]------------
   kernel BUG at include/linux/mm.h:1107!
   invalid opcode: 0000 [#1] SMP NOPTI

Please note that this change does not affect ZONE_DEVICE, because
pagetypeinfo_showmixedcount_print() is called from
mm/vmstat.c:pagetypeinfo_showmixedcount() only for populated zones, and
ZONE_DEVICE is never populated (zone->present_pages always 0).

[david@redhat.com: move check to outer loop, add comment, rephrase description]
Link: http://lkml.kernel.org/r/20191011140638.8160-1-david@redhat.com


Fixes: f1dd2cd1 ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e8
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Miles Chen <miles.chen@mediatek.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <stable@vger.kernel.org>	[4.13+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ca210ba3

mm/page_owner.c

+3 −2

Original line number	Original line	Diff line number	Diff line
	@@ -271,7 +271,8 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
	* not matter as the mixed block count will still be correct		* not matter as the mixed block count will still be correct
	*/		*/
	for (; pfn < end_pfn; ) {		for (; pfn < end_pfn; ) {
	if (!pfn_valid(pfn)) {		page = pfn_to_online_page(pfn);
			if (!page) {
	pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES);		pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES);
	continue;		continue;
	}		}
	@@ -279,13 +280,13 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
	block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);		block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
	block_end_pfn = min(block_end_pfn, end_pfn);		block_end_pfn = min(block_end_pfn, end_pfn);

	page = pfn_to_page(pfn);
	pageblock_mt = get_pageblock_migratetype(page);		pageblock_mt = get_pageblock_migratetype(page);

	for (; pfn < block_end_pfn; pfn++) {		for (; pfn < block_end_pfn; pfn++) {
	if (!pfn_valid_within(pfn))		if (!pfn_valid_within(pfn))
	continue;		continue;

			/* The pageblock is online, no need to recheck. */
	page = pfn_to_page(pfn);		page = pfn_to_page(pfn);

	if (page_zone(page) != zone)		if (page_zone(page) != zone)