I read somewhere (3.1.3) that there's a high ring (supervisor mode) and a low ring (user mode) and that some things can be run only from the highest ring.What do they mean by things? I'd guess that includes what syscalls (read/write/open... ) do but is that it? Do they think of something lower level like the eventual ASM instruction(s)?Is there a list somewhere of what is authorized in user-mode and what is not?
What is not accessible from userspace?
security;linux kernel;hardware;assembly