  Cyber Physical Systems (CPS) are characterized by their ability to integrate
the physical and information or cyber worlds. Their deployment in critical
infrastructure have demonstrated a potential to transform the world. However,
harnessing this potential is limited by their critical nature and the far
reaching effects of cyber attacks on human, infrastructure and the environment.
An attraction for cyber concerns in CPS rises from the process of sending
information from sensors to actuators over the wireless communication medium,
thereby widening the attack surface. Traditionally, CPS security has been
investigated from the perspective of preventing intruders from gaining access
to the system using cryptography and other access control techniques. Most
research work have therefore focused on the detection of attacks in CPS.
However, in a world of increasing adversaries, it is becoming more difficult to
totally prevent CPS from adversarial attacks, hence the need to focus on making
CPS resilient. Resilient CPS are designed to withstand disruptions and remain
functional despite the operation of adversaries. One of the dominant
methodologies explored for building resilient CPS is dependent on machine
learning (ML) algorithms. However, rising from recent research in adversarial
ML, we posit that ML algorithms for securing CPS must themselves be resilient.
This paper is therefore aimed at comprehensively surveying the interactions
between resilient CPS using ML and resilient ML when applied in CPS. The paper
concludes with a number of research trends and promising future research
directions. Furthermore, with this paper, readers can have a thorough
understanding of recent advances on ML-based security and securing ML for CPS
and countermeasures, as well as research trends in this active research area.
