[PATCH 5.3 153/197] hugetlbfs: dont access uninitialized memmaps in pfn_range_valid_gigantic()

[Greg Kroah-Hartman]

From: David Hildenbrand <david@xxxxxxxxxx>

commit f231fe4235e22e18d847e05cbe705deaca56580a upstream.

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

Let's make sure that we only consider online memory (managed by the
buddy) that has initialized memmaps.  ZONE_DEVICE is not applicable.

page_zone() will call page_to_nid(), which will trigger
VM_BUG_ON_PGFLAGS(PagePoisoned(page), page) with CONFIG_PAGE_POISONING
and CONFIG_DEBUG_VM_PGFLAGS when called on uninitialized memmaps.  This
can be the case when an offline memory block (e.g., never onlined) is
spanned by a zone.

Note: As explained by Michal in [1], alloc_contig_range() will verify
the range.  So it boils down to the wrong access in this function.

[1] http://lkml.kernel.org/r/20180423000943.GO17484@xxxxxxxxxxxxxx

Link: http://lkml.kernel.org/r/20191015120717.4858-1-david@xxxxxxxxxx
Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online")	[visible after d0dc12e86b319]
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reported-by: Michal Hocko <mhocko@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>	[4.13+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/hugetlb.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1084,11 +1084,10 @@ static bool pfn_range_valid_gigantic(str
 	struct page *page;
 
 	for (i = start_pfn; i < end_pfn; i++) {
-		if (!pfn_valid(i))
+		page = pfn_to_online_page(i);
+		if (!page)
 			return false;
 
-		page = pfn_to_page(i);
-
 		if (page_zone(page) != z)
 			return false;