Integers form a closed group (in the group theory sense) under multiplication and addition, so if you were concerned about specific calculations being compromised you could verify the answer via alternative calculations and testing for consistency.

Faking consistency is likely impossible without causing a huge amount other calculations (which the CPU will do as part of day-to-day operations) to fail.

Not an expert, but in theory the CPU can detect specific contexts and change its behavior. If side-channel attacks can detect AES operations, the CPU can do an even a better job.