CVE-2025-21696mm: clear uffd-wp PTE/PMD state on mremap()

Official description

In the Linux kernel, the following vulnerability has been resolved: mm: clear uffd-wp PTE/PMD state on mremap() When mremap()ing a memory region previously registered with userfaultfd as write-protected but without UFFD_FEATURE_EVENT_REMAP, an inconsistency in flag clearing leads to a mismatch between the vma flags (which have uffd-wp cleared) and the pte/pmd flags (which do not have uffd-wp cleared). This mismatch causes a subsequent mprotect(PROT_WRITE) to trigger a warning in page_table_check_pte_flags() due to setting the pte to writable while uffd-wp is still set. Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any such mremap() so that the values are consistent with the existing clearing of VM_UFFD_WP. Be careful to clear the logical flag regardless of its physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover PTE, huge PMD and hugetlb paths.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/96fed9f20481d07eba8a7fe93bc77abef178198c
• https://git.kernel.org/stable/c/8e2f6ba256dd1e590addc48e6e9577bf39c482f2
• https://git.kernel.org/stable/c/310ac886d68de661c3a334198d8604b722d7fdf8
• https://git.kernel.org/stable/c/0cef0bb836e3cfe00f08f9606c72abd72fe78ca3