You are right, I was not aware of that!

This way may actually have advantages over vDSO. Maybe you can set up IV and key with the kernel and then let the kernel do the crypto without having to have them in user space memory anymore. That would be a way to reduce risk in crypto applications, as long as you can prevent an attacker who has taken over the crypto app to retrieve the keys from the kernel. Maybe seccomp can help here.

Very exciting!