KPAC: Efficient Emulation of the ARM Pointer Authentication Instructions

ARMv8.3-A has introduced the pointer authentication (PA) feature, a new set of measures and instructions to sign and validate pointers. PA is already used and supported by the major compilers to protect the return addresses on the stack as a measure against memory corruption attacks. As more and more SoCs implement ARMv8.3-A and code compiled with PA is even fully backwards compatible on CPUs without (where the new instructions are just ignored), we can expect PA-enabled binaries to become standard in the near future. This gives rise to the question, if and how also systems without the native PA could benefit from the extra security provided by the return address protection. In this article, we explore KPAC, a set of efficient software-based approaches to bring the PA-based return-address protection onto the platforms without the hardware support in an easily adoptable (binary-compatible) and scalable manner. Technically, KPAC achieves this by either a synchronous trap-based emulation inside the kernel or an asynchronous novel memory-based invocation of a dedicated CPU core. Our experiments with the CortexSuite benchmarks, Chromium, and Memcached on a variety of platforms running Linux ranging from a Xilinx ZCU102 board over a Raspberry Pi 4 up to an 80-core Ampere Altra demonstrate the broad applicability and scalability of our approach. Furthermore, we discuss how the principles of KPAC can be generalized to the other suited problem areas.