Comment by kbolino

Even though sshd must run as root (in the usual case), it doesn't need unfettered access to kernel memory, most of the filesystem, most other processes, etc. However, you could only really sandbox sshd-as-root. In order for sshd to do its job, it does need to be able to masquerade as arbitrary non-root users. That's still pretty bad but generally not "undetectably alter the operating system or firmware" bad.