RDRAND might not be the only place where an attacker can screw me over, but it's a much easier exploit than many others, and one that is by design impossible to detect.
It would probably not be possible to get away with an XOR instruction that doesn't behave as advertised. There is simply no way to determine if RDRAND is behaving as advertised or not.
> you have to trust someone
Well, yes. Intel specifically has to my mind demonstrated beyond a shadow of a doubt that they are not be trusted (that "entire x86 core running minix --- with security holes" thing you just mentioned, thought it was ARM though). So if the only difference is moving my root of trust from Intel to a random, unknown party that is not Intel, that is already something of an improvement.
It would probably not be possible to get away with an XOR instruction that doesn't behave as advertised. There is simply no way to determine if RDRAND is behaving as advertised or not.
> you have to trust someone
Well, yes. Intel specifically has to my mind demonstrated beyond a shadow of a doubt that they are not be trusted (that "entire x86 core running minix --- with security holes" thing you just mentioned, thought it was ARM though). So if the only difference is moving my root of trust from Intel to a random, unknown party that is not Intel, that is already something of an improvement.