Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 8 Apr 2024 20:59:03 +0200 | Subject | Re: [PATCH] mm/userfaultfd: Allow hugetlb change protection upon poison entry | From | David Hildenbrand <> |
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On 06.04.24 01:19, peterx@redhat.com wrote: > From: Peter Xu <peterx@redhat.com> > > After UFFDIO_POISON, there can be two kinds of hugetlb pte markers, either > the POISON one or UFFD_WP one. > > Allow change protection to run on a poisoned marker just like !hugetlb > cases, ignoring the marker irrelevant of the permission. > > Here the two bits are mutual exclusive. For example, when install a > poisoned entry it must not be UFFD_WP already (by checking pte_none() > before such install). And it also means if UFFD_WP is set there must have > no POISON bit set. It makes sense because UFFD_WP is a bit to reflect > permission, and permissions do not apply if the pte is poisoned and > destined to sigbus. > > So here we simply check uffd_wp bit set first, do nothing otherwise. > > Attach the Fixes to UFFDIO_POISON work, as before that it should not be > possible to have poison entry for hugetlb (e.g., hugetlb doesn't do swap, > so no chance of swapin errors). > > Cc: Axel Rasmussen <axelrasmussen@google.com> > Cc: David Hildenbrand <david@redhat.com> > Cc: linux-stable <stable@vger.kernel.org> # 6.6+ > Link: https://lore.kernel.org/r/000000000000920d5e0615602dd1@google.com > Reported-by: syzbot+b07c8ac8eee3d4d8440f@syzkaller.appspotmail.com > Fixes: fc71884a5f59 ("mm: userfaultfd: add new UFFDIO_POISON ioctl") > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > mm/hugetlb.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 8267e221ca5d..ba7162441adf 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -6960,9 +6960,13 @@ long hugetlb_change_protection(struct vm_area_struct *vma, > if (!pte_same(pte, newpte)) > set_huge_pte_at(mm, address, ptep, newpte, psize); > } else if (unlikely(is_pte_marker(pte))) { > - /* No other markers apply for now. */ > - WARN_ON_ONCE(!pte_marker_uffd_wp(pte)); > - if (uffd_wp_resolve) > + /* > + * Do nothing on a poison marker; page is > + * corrupted, permissons do not apply. Here > + * pte_marker_uffd_wp()==true implies !poison > + * because they're mutual exclusive. > + */ > + if (pte_marker_uffd_wp(pte) && uffd_wp_resolve) > /* Safe to modify directly (non-present->none). */ > huge_pte_clear(mm, address, ptep, psize); > } else if (!huge_pte_none(pte)) {
Reviewed-by: David Hildenbrand <david@redhat.com>
-- Cheers,
David / dhildenb
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