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;

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