[patch 049/166] userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally

Andrew Morton
2020-04-07T03:06:32Z

From: Peter Xu <peterx@redhat.com>
Subject: userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally

Only declare _UFFDIO_WRITEPROTECT if the user specified
UFFDIO_REGISTER_MODE_WP and if all the checks passed. Then when the user
registers regions with shmem/hugetlbfs we won't expose the new ioctl to
them. Even with complete anonymous memory range, we'll only expose the
new WP ioctl bit if the register mode has MODE_WP.

Link: http://lkml.kernel.org/r/20200220163112.11409-18-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
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: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

fs/userfaultfd.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

--- a/fs/userfaultfd.c~userfaultfd-wp-declare-_uffdio_writeprotect-conditionally
+++ a/fs/userfaultfd.c
@@ -1495,14 +1495,24 @@ out_unlock:
up_write(&mm->mmap_sem);
mmput(mm);
if (!ret) {
+ __u64 ioctls_out;
+
+ ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
+ UFFD_API_RANGE_IOCTLS;
+
+ /*
+ * Declare the WP ioctl only if the WP mode is
+ * specified and all checks passed with the range
+ */
+ if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
+ ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
+
/*
* Now that we scanned all vmas we can already tell
* userland which ioctls methods are guaranteed to
* succeed on this range.
*/
- if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
- UFFD_API_RANGE_IOCTLS,
- &user_uffdio_register->ioctls))
+ if (put_user(ioctls_out, &user_uffdio_register->ioctls))
ret = -EFAULT;
}
out:
_