From 70ccb92fdd90b35bb6f9200093d4ffd6cb38156b Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Thu, 9 Mar 2017 16:17:11 -0800 Subject: userfaultfd: non-cooperative: userfaultfd_remove revalidate vma in MADV_DONTNEED userfaultfd_remove() has to be execute before zapping the pagetables or UFFDIO_COPY could keep filling pages after zap_page_range returned, which would result in non zero data after a MADV_DONTNEED. However userfaultfd_remove() may have to release the mmap_sem. This was handled correctly in MADV_REMOVE, but MADV_DONTNEED accessed a potentially stale vma (the very vma passed to zap_page_range(vma, ...)). The fix consists in revalidating the vma in case userfaultfd_remove() had to release the mmap_sem. This also optimizes away an unnecessary down_read/up_read in the MADV_REMOVE case if UFFD_EVENT_FORK had to be delivered. It all remains zero runtime cost in case CONFIG_USERFAULTFD=n as userfaultfd_remove() will be defined as "true" at build time. Link: http://lkml.kernel.org/r/20170302173738.18994-3-aarcange@redhat.com Signed-off-by: Andrea Arcangeli Acked-by: Mike Rapoport Cc: "Dr. David Alan Gilbert" Cc: Mike Kravetz Cc: Pavel Emelyanov Cc: Hillf Danton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/madvise.c | 44 +++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 41 insertions(+), 3 deletions(-) (limited to 'mm') diff --git a/mm/madvise.c b/mm/madvise.c index dc5927c812d3..7a2abf0127ae 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -513,7 +513,43 @@ static long madvise_dontneed(struct vm_area_struct *vma, if (!can_madv_dontneed_vma(vma)) return -EINVAL; - userfaultfd_remove(vma, prev, start, end); + if (!userfaultfd_remove(vma, start, end)) { + *prev = NULL; /* mmap_sem has been dropped, prev is stale */ + + down_read(¤t->mm->mmap_sem); + vma = find_vma(current->mm, start); + if (!vma) + return -ENOMEM; + if (start < vma->vm_start) { + /* + * This "vma" under revalidation is the one + * with the lowest vma->vm_start where start + * is also < vma->vm_end. If start < + * vma->vm_start it means an hole materialized + * in the user address space within the + * virtual range passed to MADV_DONTNEED. + */ + return -ENOMEM; + } + if (!can_madv_dontneed_vma(vma)) + return -EINVAL; + if (end > vma->vm_end) { + /* + * Don't fail if end > vma->vm_end. If the old + * vma was splitted while the mmap_sem was + * released the effect of the concurrent + * operation may not cause MADV_DONTNEED to + * have an undefined result. There may be an + * adjacent next vma that we'll walk + * next. userfaultfd_remove() will generate an + * UFFD_EVENT_REMOVE repetition on the + * end-vma->vm_end range, but the manager can + * handle a repetition fine. + */ + end = vma->vm_end; + } + VM_WARN_ON(start >= end); + } zap_page_range(vma, start, end - start); return 0; } @@ -554,8 +590,10 @@ static long madvise_remove(struct vm_area_struct *vma, * mmap_sem. */ get_file(f); - userfaultfd_remove(vma, prev, start, end); - up_read(¤t->mm->mmap_sem); + if (userfaultfd_remove(vma, start, end)) { + /* mmap_sem was not released by userfaultfd_remove() */ + up_read(¤t->mm->mmap_sem); + } error = vfs_fallocate(f, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, offset, end - start); -- cgit v1.2.3