We consider quasi one-dimensional RKKY systems in proximity to an s-wave superconductor. We show that a \(2k_F\)-peak in the spin susceptibility of the superconductor in the one-dimensional limit supports helical order of localized magnetic moments via RKKY interaction, where \(k_F\) is the Fermi wavevector. The magnetic helix is equivalent to a uniform magnetic field and very strong spin-orbit interaction (SOI) with an effective SOI length \(1/2k_F\). We find the conditions to establish such a magnetic state in atomic chains and semiconducting nanowires with magnetic atoms or nuclear spins. Generically, these systems are in a topological phase with Majorana fermions. The inherent self-tuning of the helix to \(2k_F\) eliminates the need to tune the chemical potential.