  Cyber-physical systems (CPS) have experienced rapid growth in recent decades.
However, like any other computer-based systems, malicious attacks evolve
mutually, driving CPS to undesirable physical states and potentially causing
catastrophes. Although the current state-of-the-art is well aware of this
issue, the majority of researchers have not focused on CPS recovery, the
procedure we defined as restoring a CPS's physical state back to a target
condition under adversarial attacks. To call for attention on CPS recovery and
identify existing efforts, we have surveyed a total of 30 relevant papers. We
identify a major partition of the proposed recovery strategies: shallow
recovery vs. deep recovery, where the former does not use a dedicated recovery
controller while the latter does. Additionally, we surveyed exploratory
research on topics that facilitate recovery. From these publications, we
discuss the current state-of-the-art of CPS recovery, with respect to
applications, attack type, attack surfaces and system dynamics. Then, we
identify untouched sub-domains in this field and suggest possible future
directions for researchers.
