new helper: uaccess_kernel()

BugLink: https://bugs.launchpad.net/bugs/1810958

commit db68ce10 upstream.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[only take the include/linux/uaccess.h portion - gregkh]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

include/linux/uaccess.h

@@ -2,6 +2,9 @@
 #define __LINUX_UACCESS_H__
 
 #include <linux/sched.h>
+
+#define uaccess_kernel() segment_eq(get_fs(), KERNEL_DS)
+
 #include <asm/uaccess.h>
 
 static __always_inline void pagefault_disabled_inc(void)