Re: Privilege Levels Below User

John Savard <quadibloc@servername.invalid> writes:

This may be a silly idea... but it seems to be the sort of thing that
current concerns about computer security may be calling for.
>
It is typical for computers to have a privileged mode of operation,
wherein I/O operations and certain special changes to the state of the
computer are allowed that are barred to normal computational  tasks.
>
For various reasons, miscreants have not been completely foiled by the
existence of this feature.
>
Some types of instruction that are required for normal computation are
still, to a certain extent, potentially harmful.
>
So I am thinking it might be useful to have, for example, two states
less privileged than the user state, and some mechanism for user
programs to call subroutines which are in that state until they return
- the return instruction being limited, sort of like a supervisor
call, so it can only return in a proper manner.

There are already more than five security rings in most
processors.

Intel:   Ring 3, Ring 2 (unused), Ring 1(unused), Ring 0, VMX, Enclave,
 SMM

AMD:     Ring 3, Ring 2 (unused), Ring 1(unused), Ring 0, SVM, SMM

ARM64:   Realm Monitor, EL3 (Secure monitor), EL2(Hypervisor), EL1
(Kernel), EL0 (user)

<snip description of useless feature>