> our proposed attacker has the ability to embed malicious hardware and/or microcode in your CPU which can access to the full contents of RAM and all CPU regist

> our proposed attacker has the ability to embed malicious hardware and/or microcode in your CPU which can access to the full contents of RAM and all CPU registers If the threat model under which rdrand can achieve cancelling XORs is one which requires the threat to have access to RAM and CPU registers, combating it by removing rdrand is like demanding the removal of a front gate that's breakable using teleportation. If the attacker has teleportation, forget the gate, they can teleport straight into your house. As Ted Ts'o points out elsewhere in thread, "if the microcode can figure out where the entropy pool is and figure out what it's being XOR'ed with and adjust accordingly, you're toast anyway. No matter what you can do, if the adversary has control of the cpu microcode at that level, the adversary can just modify the returned entropy value in memory".