[$] /dev/userfaultfd

The userfaultfd()system call allows one thread to handle page faults for another in userspace. It has a number of interesting use cases, including the livemigration of virtual machines. There are also some less appealing usecases, though, most of which are appreciated by attackers trying to takecontrol of a machine. Attempts have been made over the years to makeuserfaultfd() less useful as an exploit tool, but thispatch set from Axel Rasmussen takes a different approach bycircumventing the system call entirely.