This paper introduces a formal workflow for modeling software/hardware systems in order to explore the effects of fault injections and evaluate the robustness to fault injection attacks. We illustrate this workflow on four versions of a PIN authentication code, embedding different software countermeasures. The code is symbolically evaluated on two implementations of the RISC-V CV32E40P core: the original implementation from the OpenHW group and an implementation that integrates protection of the pipeline control signals. On the original, unprotected core, our formal workflow exposes various vulnerabilities, including previously unknown ones, whereas, on the protected core, it confirms the effectiveness of the proposed countermeasures.