Salus: Non-hierarchical Memory Access Rights to Enforce the Principle of Least Privilege

Consumer devices are increasingly being used to perform security and privacy critical tasks. The software used to perform these tasks is often vulnerable to attacks, due to bugs in the application itself or in included software libraries. Recent work proposes the isolation of security-sensitive parts of applications into protected modules, each of which can only be accessed through a predefined public interface. But most parts of an application can be considered security-sensitive at some level, and an attacker that is able to gain in-application level access may be able to abuse services from protected modules. We propose Salus, a Linux kernel modification that provides a novel approach for partitioning processes into isolated compartments. By enabling compartments to restrict the system calls they are allowed to perform and to authenticate their callers and callees, the impact of unsafe interfaces and vulnerable compartments is significantly reduced. We describe the design of Salus, report on a prototype implementation and evaluate it in terms of security and performance. We show that Salus provides a significant security improvement with a low performance overhead, without relying on any non-standard hardware support.