[patch 14/26] hugetlbfs: don't access uninitialized memmaps in pfn_range_valid_gigantic()

[akpm@linux-foundation.org]

From: David Hildenbrand <david@redhat.com>
Subject: hugetlbfs: don't access uninitialized memmaps in pfn_range_valid_gigantic()

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@dhcp22.suse.cz

Link: http://lkml.kernel.org/r/20191015120717.4858-1-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: Michal Hocko <mhocko@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: <stable@vger.kernel.org>	[4.13+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/mm/hugetlb.c~hugetlbfs-dont-access-uninitialized-memmaps-in-pfn_range_valid_gigantic
+++ a/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;
 
_