[PATCH 4/6] mm/userfaultfd: Fail uffd-wp registeration if not supported

[Peter Xu <peterx@redhat.com>]

We should fail uffd-wp registration immediately if the arch does not even have
CONFIG_HAVE_ARCH_USERFAULTFD_WP defined.  That'll block also relevant ioctls on
e.g. UFFDIO_WRITEPROTECT because that'll check against VM_UFFD_WP, which can
only be applied with a success registration.

Remove the WP feature bit too for those archs when handling UFFDIO_API ioctl.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 fs/userfaultfd.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 14f92285d04f8..5dd78238cc156 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1304,8 +1304,12 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	vm_flags = 0;
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
 		vm_flags |= VM_UFFD_MISSING;
-	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)
+	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
+#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+		goto out;
+#endif
 		vm_flags |= VM_UFFD_WP;
+	}
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
 		goto out;
@@ -1942,6 +1946,9 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 	uffdio_api.features = UFFD_API_FEATURES;
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
 	uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS;
+#endif
+#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+	uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
 #endif
 	uffdio_api.ioctls = UFFD_API_IOCTLS;
 	ret = -EFAULT;
-- 
2.26.2