RISC-V Global Forum 2020

Although Trusted Execution Environments (TEEs) can be built using the standard RISC-V machine mode as the trusted state this approach has some limitations:
- Machine mode must manage the lower privilege tasks, exceptions/interrupts and device drivers as well as managing secret data and providing trusted services. This dual use violates the security Principle of Least Privilege.
- Supporting all these mechanisms make the code large, increasing the risk of security loopholes appearing and providing more opportunity to create gadgets for ROP/JOP style attacks.
- Transitions between insecure and secure domains is inevitablly heavyweight as it must be syscall based.
This extension addresses these issues by adding a new Trusted Execution State which provides stronger protection and quicker handling of secret data.