[patch 044/166] userfaultfd: wp: support write protection for userfault vma range

Andrew Morton
2020-04-07T03:06:12Z

From: Shaohua Li <shli@fb.com>
Subject: userfaultfd: wp: support write protection for userfault vma range

Add API to enable/disable writeprotect a vma range. Unlike mprotect, this
doesn't split/merge vmas.

[peterx@redhat.com:
- use the helper to find VMA;
- return -ENOENT if not found to match mcopy case;
- use the new MM_CP_UFFD_WP* flags for change_protection
- check against mmap_changing for failures
- replace find_dst_vma with vma_find_uffd]
Link: http://lkml.kernel.org/r/20200220163112.11409-13-peterx@redhat.com
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/userfaultfd_k.h | 3 +
mm/userfaultfd.c | 54 ++++++++++++++++++++++++++++++++
2 files changed, 57 insertions(+)

--- a/include/linux/userfaultfd_k.h~userfaultfd-wp-support-write-protection-for-userfault-vma-range
+++ a/include/linux/userfaultfd_k.h
@@ -41,6 +41,9 @@ extern ssize_t mfill_zeropage(struct mm_
unsigned long dst_start,
unsigned long len,
bool *mmap_changing);
+extern int mwriteprotect_range(struct mm_struct *dst_mm,
+ unsigned long start, unsigned long len,
+ bool enable_wp, bool *mmap_changing);

/* mm helpers */
static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma,
--- a/mm/userfaultfd.c~userfaultfd-wp-support-write-protection-for-userfault-vma-range
+++ a/mm/userfaultfd.c
@@ -638,3 +638,57 @@ ssize_t mfill_zeropage(struct mm_struct
{
return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing, 0);
}
+
+int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
+ unsigned long len, bool enable_wp, bool *mmap_changing)
+{
+ struct vm_area_struct *dst_vma;
+ pgprot_t newprot;
+ int err;
+
+ /*
+ * Sanitize the command parameters:
+ */
+ BUG_ON(start & ~PAGE_MASK);
+ BUG_ON(len & ~PAGE_MASK);
+
+ /* Does the address range wrap, or is the span zero-sized? */
+ BUG_ON(start + len <= start);
+
+ down_read(&dst_mm->mmap_sem);
+
+ /*
+ * If memory mappings are changing because of non-cooperative
+ * operation (e.g. mremap) running in parallel, bail out and
+ * request the user to retry later
+ */
+ err = -EAGAIN;
+ if (mmap_changing && READ_ONCE(*mmap_changing))
+ goto out_unlock;
+
+ err = -ENOENT;
+ dst_vma = find_dst_vma(dst_mm, start, len);
+ /*
+ * Make sure the vma is not shared, that the dst range is
+ * both valid and fully within a single existing vma.
+ */
+ if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
+ goto out_unlock;
+ if (!userfaultfd_wp(dst_vma))
+ goto out_unlock;
+ if (!vma_is_anonymous(dst_vma))
+ goto out_unlock;
+
+ if (enable_wp)
+ newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
+ else
+ newprot = vm_get_page_prot(dst_vma->vm_flags);
+
+ change_protection(dst_vma, start, start + len, newprot,
+ enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE);
+
+ err = 0;
+out_unlock:
+ up_read(&dst_mm->mmap_sem);
+ return err;
+}
_