Not all Faster Than Light (FTL) drives violate causality. Alcubierre drive does not since this spacetime is Lorentzian and does not allow for closed timelike curves (CTC). Allen E. Everett and Thomas A. Roman 1 demonstrated that with two non-overlapping Krasnikov tubes 2, it is possible to construct a time machine.
The Krasnikov tube is a FTL drive proposed by S.V. Krasnikov with metric $$ds^2 = - dt^2 + (1 - k) dx dt + k dx^2 \,,$$ where k = k(t,x) can be determined in terms of step functions, describing a junction of three regions in spacetime resembling a tube. The outside region is flat, with two simple killing fields determined by time and space translations defining lightcones. The transition region is the only one that is curved. The interior region is also flat, with killing fields that are linear combinations of space and time translations. Still, one of these fields carries a proportionality factor that can be taken arbitrarily small, giving the lightcones a 'wider' opening. This interior lightcone does not possess an event horizon like the Alcubierre warp drive metric.
Everett and Roman demonstrated that one Krasnikov tube does not possess issues with causality, but two Krasnikov tubes can create a time machine with causality violation, causing CTC. This time machine can only allow going backward in time, though. This CTC can be avoided with boundary conditions on the Krasnikov metric. imposing limitations on the direction of movement for the observers inside the tube. Sort of like a 'one-way tube'; once the observers start moving, they can never return to the departure point.
[1] A Superluminal Subway: The Krasnikov Tube
[2] Hyperfast Interstellar Travel in General Relativity