The patch titled Subject: userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry has been added to the -mm mm-hotfixes-unstable branch. Its filename is userfaultfd-fix-a-crash-in-uffdio_move-when-pmd-is-a-migration-entry.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Suren Baghdasaryan surenb@google.com Subject: userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry Date: Wed, 6 Aug 2025 15:00:22 -0700

When UFFDIO_MOVE encounters a migration PMD entry, it proceeds with obtaining a folio and accessing it even though the entry is swp_entry_t. Add the missing check and let split_huge_pmd() handle migration entries.

Link: https://lkml.kernel.org/r/20250806220022.926763-1-surenb@google.com Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Peter Xu peterx@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: David Hildenbrand david@redhat.com Cc: Lokesh Gidra lokeshgidra@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/userfaultfd.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)

--- a/mm/userfaultfd.c~userfaultfd-fix-a-crash-in-uffdio_move-when-pmd-is-a-migration-entry +++ a/mm/userfaultfd.c @@ -1821,13 +1821,16 @@ ssize_t move_pages(struct userfaultfd_ct /* Check if we can move the pmd without splitting it. */ if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || !pmd_none(dst_pmdval)) { - struct folio *folio = pmd_folio(*src_pmd); + /* Can be a migration entry */ + if (pmd_present(*src_pmd)) { + struct folio *folio = pmd_folio(*src_pmd);

- if (!folio || (!is_huge_zero_folio(folio) && - !PageAnonExclusive(&folio->page))) { - spin_unlock(ptl); - err = -EBUSY; - break; + if (!folio || (!is_huge_zero_folio(folio) && + !PageAnonExclusive(&folio->page))) { + spin_unlock(ptl); + err = -EBUSY; + break; + } }

spin_unlock(ptl); _

Patches currently in -mm which might be from surenb@google.com are

userfaultfd-fix-a-crash-in-uffdio_move-when-pmd-is-a-migration-entry.patch mm-limit-the-scope-of-vma_start_read.patch mm-change-vma_start_read-to-drop-rcu-lock-on-failure.patch