It is, however, in principle possible to prove that a processor implements the spec and only the spec; seach for "formal verification risc v" to find out more.
Of course if someone can sneak a backdoor into the spec, all bets are off.
Of course if someone can sneak a backdoor into the spec, all bets are off.
For example, even if everything was provably manufactured to spec, it could be laid out in a way that exposes side channels, enables rowhammer-like attacks, and so on.