7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Josef Bacik [ Upstream commit f61e1cf15fb44f9cf89d43d8ef01f926322bb1c4 ] hugetlb_fault() resolves the uffd bit on a write fault only if the VMA is registered for userfaultfd write protection, and hugetlb_wp() bails out for any entry with the uffd bit set assuming hugetlb_fault() has already resolved it. When a read-only hugetlb entry with the uffd bit set is mapped in a VMA that is not registered for uffd-wp, a write fault to it never makes progress. If the access comes from the kernel, e.g. read(2) from /dev/zero into such page, the task spins in the page fault handler, ignores SIGKILL and keeps holding the locks taken by the system call. Such entries should not exist, but an unprivileged user can create them, for example with MADV_DONTNEED of a page protected with UFFDIO_RWPROTECT or with UFFDIO_COPY in MODE_WP racing with UFFDIO_UNREGISTER. Clear the uffd bit when the VMA is not registered for uffd-wp and let the fault proceed to hugetlb_wp(), like do_wp_page() does for regular pages. Note that a FOLL_FORCE write to a page protected with UFFDIO_RWPROTECT in a private VMA that was made PROT_NONE now drops the RWP protection of that page. Original fix generated by an LLM and sent in private by Josef. [rppt@kernel.org: massage commit message] [david@kernel.org: convert comment into a TODO] Link: https://lore.kernel.org/20261015-urgent_fixes-v1-6-42796911043b@kernel.org Fixes: 60d5b473d61b ("mm/hugetlb: fix uffd wr-protection for CoW optimization path") Signed-off-by: Josef Bacik Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Mike Rapoport (Microsoft) Signed-off-by: Andrew Morton Reported-by: Chris Mason Acked-by: Lorenzo Stoakes (ARM) Reviewed-by: Lance Yang Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Jann Horn Cc: Pedro Falcato Cc: Muchun Song Cc: Oscar Salvador Cc: Miaohe Lin Cc: Naoya Horiguchi Cc: Adam Litke Cc: Mel Gorman Cc: Rik van Riel Cc: Peter Xu Cc: Kiryl Shutsemau Cc: Signed-off-by: Sasha Levin --- mm/hugetlb.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index fb7205c703b3f..81e6c98d21a4e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6190,15 +6190,19 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, goto out_ptl; /* Handle userfault-wp first, before trying to lock more pages */ - if (userfaultfd_wp(vma) && huge_pte_uffd(huge_ptep_get(mm, vmf.address, vmf.pte)) && + if (huge_pte_uffd(huge_ptep_get(mm, vmf.address, vmf.pte)) && (flags & FAULT_FLAG_WRITE) && !huge_pte_write(vmf.orig_pte)) { - if (!userfaultfd_wp_async(vma)) { + if (userfaultfd_wp(vma) && !userfaultfd_wp_async(vma)) { spin_unlock(vmf.ptl); hugetlb_vma_unlock_read(vma); mutex_unlock(&hugetlb_fault_mutex_table[hash]); return handle_userfault(&vmf, VM_UFFD_WP); } + /* + * TODO: fix all cases where uffd PTE bits remain in VMAs that + * are no longer registered with uffd. + */ vmf.orig_pte = huge_pte_clear_uffd(vmf.orig_pte); set_huge_pte_at(mm, vmf.address, vmf.pte, vmf.orig_pte, huge_page_size(hstate_vma(vma))); -- 2.53.0