Comment by twoodfin

What I’m looking for is a way for a process to de/re-escalate its privileges to access memory, without an expensive context switch being required at the transition. The CPU would simply enforce different rules based on (say) the high-order bits of the instruction pointer.

Imagine a server process that wants to run some elaborate third-party content parser. It’d be great to be sure that no matter how buggy or malicious that code, it can’t leak the TLS keys.

Today, high-security architectures must use process isolation to achieve this kind of architectural guarantee, but even finely tuned IPC like L4’s is an order of magnitude slower than a predictable jump.