Swarm of drones can be affected by cyber-physical attacks. Adversaries can get control over the individual drones, and disrupt the swarm from succeeding its mission. We present a path planning algorithm for drone swarms. None of the drones have to know in advance the entire path and final destination. However, together they collectively determine and unravel step-by-step the path and final destination, resolving a localization problem at each step. The algorithm presented allows for shared-information path planning through waypoints and is fault-tolerant and resilient to drones whose GPS may be malfunctioning due to cyber-physical hack attacks. We have validated our algorithm with appropriate simulations, implemented over OMNeT++, OS3 and GNSSim, which allow building network simulations including GPS attacks (e.g., jamming and spoofing attacks). The OMNeT++ models and the GNSSim functions are linked together, to validate our work.