From: Peter Xu peterx@redhat.com
commit 49d6d7fb631345b0f2957a7c4be24ad63903150f upstream.
Patch series "mm: Fixes on pte markers".
Patch 1 resolves the syzkiller report from Pengfei.
Patch 2 further harden pte markers when used with the recent swapin error markers. The major case is we should persist a swapin error marker after fork(), so child shouldn't read a corrupted page.
This patch (of 2):
When fork(), dst_vma is not guaranteed to have VM_UFFD_WP even if src may have it and has pte marker installed. The warning is improper along with the comment. The right thing is to inherit the pte marker when needed, or keep the dst pte empty.
A vague guess is this happened by an accident when there's the prior patch to introduce src/dst vma into this helper during the uffd-wp feature got developed and I probably messed up in the rebase, since if we replace dst_vma with src_vma the warning & comment it all makes sense too.
Hugetlb did exactly the right here (copy_hugetlb_page_range()). Fix the general path.
Reproducer:
https://github.com/xupengfe/syzkaller_logs/blob/main/221208_115556_copy_page...
Bugzilla report: https://bugzilla.kernel.org/show_bug.cgi?id=216808
Link: https://lkml.kernel.org/r/20221214200453.1772655-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20221214200453.1772655-2-peterx@redhat.com Fixes: c56d1b62cce8 ("mm/shmem: handle uffd-wp during fork()") Signed-off-by: Peter Xu peterx@redhat.com Reported-by: Pengfei Xu pengfei.xu@intel.com Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Miaohe Lin linmiaohe@huawei.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: "Huang, Ying" ying.huang@intel.com Cc: Nadav Amit nadav.amit@gmail.com Cc: stable@vger.kernel.org # 5.19+ Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/memory.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
--- a/mm/memory.c +++ b/mm/memory.c @@ -875,12 +875,8 @@ copy_nonpresent_pte(struct mm_struct *ds return -EBUSY; return -ENOENT; } else if (is_pte_marker_entry(entry)) { - /* - * We're copying the pgtable should only because dst_vma has - * uffd-wp enabled, do sanity check. - */ - WARN_ON_ONCE(!userfaultfd_wp(dst_vma)); - set_pte_at(dst_mm, addr, dst_pte, pte); + if (userfaultfd_wp(dst_vma)) + set_pte_at(dst_mm, addr, dst_pte, pte); return 0; } if (!userfaultfd_wp(dst_vma))