From f4f0a3d85b50a65a348e2b8635041d6b30f01deb Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Wed, 29 Nov 2017 16:11:30 -0800 Subject: mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine I made a mistake during converting hugetlb code to 5-level paging: in huge_pte_alloc() we have to use p4d_alloc(), not p4d_offset(). Otherwise it leads to crash -- NULL-pointer dereference in pud_alloc() if p4d table is not yet allocated. It only can happen in 5-level paging mode. In 4-level paging mode p4d_offset() always returns pgd, so we are fine. Link: http://lkml.kernel.org/r/20171122121921.64822-1-kirill.shutemov@linux.intel.com Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging") Signed-off-by: Kirill A. Shutemov Acked-by: Vlastimil Babka Acked-by: Michal Hocko Cc: [4.11+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'mm') diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 698e8fb34031..9a334f5fb730 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4635,7 +4635,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, pte_t *pte = NULL; pgd = pgd_offset(mm, addr); - p4d = p4d_offset(pgd, addr); + p4d = p4d_alloc(mm, pgd, addr); + if (!p4d) + return NULL; pud = pud_alloc(mm, p4d, addr); if (pud) { if (sz == PUD_SIZE) { -- cgit v1.2.3