CPU Bugs, CPU Backdoors and Consequences on Security

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Abstract

In this paper, we present the consequences on the security of operating systems and virtual machine monitors of the presence of a bug or a backdoor in x86 processors. We will not try to determine whether the backdoor threat is realistic or not, but we will assume that a bug or a backdoor exists and analyse the consequences on systems. We will show how it is possible for an attacker to implement a simple and generic CPU backdoor to be later able to bypass mandatory security mechanisms with very limited initial privileges. We will explain practical difficulties and show proof of concept schemes using a modified Qemu CPU emulator. Backdoors studied in this paper are all usable from the software level without any physical access to the hardware.