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

Commit Message

Andrew Morton Oct. 19, 2019, 3:20 a.m. UTC

From: David Hildenbrand <[e-mail]>
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/[e-mail]

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online")	[visible after d0dc12e86b319]
Signed-off-by: David Hildenbrand <[e-mail]>
Reported-by: Michal Hocko <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Reviewed-by: Mike Kravetz <[e-mail]>
Cc: Anshuman Khandual <[e-mail]>
Cc: <[e-mail]>	[4.13+]
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- 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;