On 30/06/25 8:49 am, Sasha Levin wrote:

When handling non-swap entries in move_pages_pte(), the error handling for entries that are NOT migration entries fails to unmap the page table entries before jumping to the error handling label.

This results in a kmap/kunmap imbalance which on CONFIG_HIGHPTE systems triggers a WARNING in kunmap_local_indexed() because the kmap stack is corrupted.

Example call trace on ARM32 (CONFIG_HIGHPTE enabled): WARNING: CPU: 1 PID: 633 at mm/highmem.c:622 kunmap_local_indexed+0x178/0x17c Call trace: kunmap_local_indexed from move_pages+0x964/0x19f4 move_pages from userfaultfd_ioctl+0x129c/0x2144 userfaultfd_ioctl from sys_ioctl+0x558/0xd24

The issue was introduced with the UFFDIO_MOVE feature but became more frequent with the addition of guard pages (commit 7c53dfbdb024 ("mm: add PTE_MARKER_GUARD PTE marker")) which made the non-migration entry code path more commonly executed during userfaultfd operations.

Fix this by ensuring PTEs are properly unmapped in all non-swap entry paths before jumping to the error handling label, not just for migration entries.

Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Cc: stable@vger.kernel.org Signed-off-by: Sasha Levin sashal@kernel.org

---

mm/userfaultfd.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 8253978ee0fb1..7c298e9cbc18f 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1384,14 +1384,15 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, entry = pte_to_swp_entry(orig_src_pte); if (non_swap_entry(entry)) {

• 	pte_unmap(src_pte);
  

• 	pte_unmap(dst_pte);
  

• 	src_pte = dst_pte = NULL;
  if (is_migration_entry(entry)) {
  

• 		pte_unmap(src_pte);
  

• 		pte_unmap(dst_pte);
  

• 		src_pte = dst_pte = NULL;
  	migration_entry_wait(mm, src_pmd, src_addr);
  	err = -EAGAIN;
  

• 	} else
  

• 	} else {
  	err = -EFAULT;
  

• 	}
  goto out;
  

Won't the out label take care of the unmapping? I think CONFIG_HIGHPTE is involved in the explanation.

}