Messages in this thread | | | Subject | Re: [PATCH] mm/hugetlb: Fix NULL-pointer dereference on 5-level paging machine | From | Vlastimil Babka <> | Date | Wed, 22 Nov 2017 13:36:43 +0100 |
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On 11/22/2017 01:19 PM, Kirill A. Shutemov wrote: > I've made 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. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging") > Cc: <stable@vger.kernel.org> # v4.11+
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> --- > mm/hugetlb.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 2d2ff5e8bf2b..94a4c0b63580 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4617,7 +4617,9 @@ 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) { >
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