Protecting the Stack with Metadata Policies and Tagged Hardware

The program call stack is a major source of exploitable security vulnerabilities in low-level, unsafe languages like C. In conventional runtime implementations, the underlying stack data is exposed and unprotected, allowing programming errors to turn into security violations. In this work, we design novel metadata-tag based, stack-protection security policies for a general-purpose tagged architecture. Our policies specifically exploit the natural locality of dynamic program call graphs to achieve cacheability of the metadata rules that they require. Our simple Return Address Protection policy has a performance overhead of 1.2% but just protects return addresses. The two richer policies we present, Static Authorities and Depth Isolation, provide object-level protection for all stack objects. When enforcing memory safety, our Static Authorities policy has a performance overhead of 5.7% and our Depth Isolation policy has a performance overhead of 4.5%. When enforcing data-flow integrity (DFI), in which we only detect a violation when a corrupted value is read, our Static Authorities policy has a performance overhead of 3.6% and our Depth Isolation policy has a performance overhead of 2.4%. To characterize our policies, we provide a stack threat taxonomy and show which threats are prevented by both prior work protection mechanisms and our policies.