Yes, exactly. Multics actually tried, here's a memo from 1974 discussing the issue: https://multicians.org/mtbs/mtb696.html https://multicians.org/mtbs/mtb696.h

Yes, exactly. Multics actually tried, here's a memo from 1974 discussing the issue: https://multicians.org/mtbs/mtb696.html https://multicians.org/mtbs/mtb696.html Paged shared libraries, signalling by ramping up and down CPU usage, there are an enormous number of possible covert channels.