Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Thu, 11 Jan 2024 17:39:35 -0800 | Subject | [PATCH 1/1] userfaultfd: avoid huge_zero_page in UFFDIO_MOVE | From | Suren Baghdasaryan <> |
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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; + } /* Check if we can move the pmd without splitting it. */ if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || -- 2.43.0.275.g3460e3d667-goog
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