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

Commit Message

Andrew Morton April 7, 2020, 3:06 a.m. UTC

From: Peter Xu <[e-mail]>
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/[e-mail]
Signed-off-by: Peter Xu <[e-mail]>
Reviewed-by: Mike Rapoport <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Bobby Powers <[e-mail]>
Cc: Brian Geffon <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Denis Plotnikov <[e-mail]>
Cc: "Dr . David Alan Gilbert" <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Jerome Glisse <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: "Kirill A . Shutemov" <[e-mail]>
Cc: Martin Cracauer <[e-mail]>
Cc: Marty McFadden <[e-mail]>
Cc: Maya Gokhale <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Cc: Pavel Emelyanov <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Shaohua Li <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- 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: