Hazardous Behavior Analysis for Complex Pre-Existing Software in Safety-Critical Context: Approach and Application to the Linux Dynamic Memory Allocator

As system designers are transitioning to the usage of pre-existing software architectural elements to reduce time-to-market and costs, they face challenges in safety-critical applications. Pre-existing software may have been implemented without following any safety and/or quality standard, and its documentation may be incomplete or unclear. As recommended by part 6 of the functional safety standard ISO 26262 (product development at the software level), stringent rules and guidelines must be followed during the implementation of a new software. The qualification of a pre-existing software according to ISO 26262 may hence be very time consuming and expensive if not addressed in a structured way. This work presents STPA for Pre-existing Software (STPA-PES), a new software hazardous behavior analysis approach designed to identify criticalities or abnormal conditions in complex pre-existing software to be mitigated with adequate safety measures. The major challenge in such a process consists in the definition of a model that correctly represents the system under analysis when the architectural design of pre-existing software is not available. As a relevant example, the proposed approach is finally applied to dynamic memory allocator (DynMA) in Linux kernel to show how STPA-PES is able to derive safety requirements of this software architectural element.