Messages in this thread | | | Date | Fri, 12 Jan 2024 09:57:12 +0100 | Subject | Re: [PATCH 1/1] userfaultfd: avoid huge_zero_page in UFFDIO_MOVE | From | David Hildenbrand <> |
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On 12.01.24 02:39, Suren Baghdasaryan wrote: > While testing UFFDIO_MOVE ioctl, syzbot triggered VM_BUG_ON_PAGE caused > by a call to PageAnonExclusive() with a huge_zero_page as a parameter. > UFFDIO_MOVE does not yet handle zeropages and returns EBUSY when one is > encountered. Add an early huge_zero_page check in the PMD move path > to avoid this situation. > > Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > --- > Applies cleanly over linux-next, mm-stable and mm-unstable branches > > mm/userfaultfd.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 216ab4c8621f..20e3b0d9cf7e 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -1393,6 +1393,12 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, > err = -ENOENT; > break; > } > + /* Avoid moving zeropages for now */ > + if (is_huge_zero_pmd(*src_pmd)) { > + spin_unlock(ptl); > + err = -EBUSY; > + break; > + }
As an alternative (and more future proof?) just reject anything that is not an anon folio as well?
Anyhow, this should handle the issue at hand.
Acked-by: David Hildenbrand <david@redhat.com>
-- Cheers,
David / dhildenb
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