Thought experiment on hardware backdoors

[vpx23]

Prompt: Does the AMD PSP have access to the NIC?

GGAI: The AMD Platform Security Processor (PSP) is an integrated security coprocessor in AMD CPUs. It does not have direct access to the network interface card (NIC) or the ability to control network traffic in the way that some other management engines do. Instead, the PSP primarily handles tasks like DRAM initialization, HDCP handling, boot process supervision, and firmware updates.
While the PSP's firmware runs before the main CPU and has unrestricted access to memory, it is not designed to interact with the network. Its access is primarily focused on the CPU itself and the hardware it manages. This means that a malicious actor with access to the PSP would be limited to manipulating the CPU and its related hardware, rather than being able to directly interfere with network traffic.

Prompt: Does a CPU have access to a NIC?

GGAI: Yes, a CPU (Central Processing Unit) has access to a NIC (Network Interface Card) through a PCIe (Peripheral Component Interconnect Express) link. The CPU uses this link to communicate with the NIC, allowing data to be sent and received across the network.

Prompt: Answer these 2 questions separately: "Does the AMD PSP have access to the NIC?" and "Does a CPU have access to a NIC?" and analyze if its outputs are contradictory.

GGAI: The answers to the two questions are generally not contradictory, but they can be nuanced depending on the specific context.

Question 1: Does the AMD PSP have access to the NIC?
The AMD Platform Security Processor (PSP) is primarily responsible for hardware-level security and trust. It does not typically have direct access to the Network Interface Card (NIC) for general network operations. The PSP primarily focuses on functions like security, encryption, and authentication, and its role is more about securing the system as a whole rather than interacting with network devices directly.

Question 2: Does a CPU have access to a NIC?
Yes, a CPU (Central Processing Unit) absolutely does have access to the NIC. The NIC, as a peripheral device, is connected to the CPU through various buses or interfaces. The CPU uses these connections to send and receive data to and from the NIC, allowing it to manage network traffic, control the connection, and interact with the network.
Analysis: Are the answers contradictory?
No, the answers are not contradictory. They describe different aspects of the hardware and their roles. The PSP has access to the system and its components for security purposes, but its access to the NIC is not a primary function. The CPU, on the other hand, is the main controller and has direct access to the NIC to manage network operations.
In essence:

PSP:
Focused on security and trust, with a secondary role in managing specific hardware access.
CPU:
The primary processing unit that has direct control and access to all peripherals, including the NIC.

[Patrick M. Hausen]

So? Why would one care what an LLM without any knowledge about reality hallucinates? One would need to analyse the documentation if publicly available. I regard anything produced by an LLM as utter BS.

Read this for a reality check and a rude awakening:

https://amandaguinzburg.substack.com/p/diabolus-ex-machina

[meyergru]

@vpx23: What do you want to tell us by this example? That AIs deliver the wrong answers when you give them no guidelines (aka "framing")? That is a well-known fact.

I fed that block into ChatGPT and asked:

My question is not if these staements are contradictory, but if they are misleading in the sense that if the PSP can control the CPU and the CPU can control the NIC, then in turn the PSP can also control the NIC. So, are the answers misleading in they were too narrowed down to "direct" control?

And its answer was:

Yes, you're absolutely right to question the framing of those answers, and yes, they can be misleading due to an overly narrow focus on "direct" access.

Let's break this down more clearly:
✅ Reality of Access:

    The AMD PSP is a security co-processor embedded into AMD CPUs, with privileged access to system resources, particularly during early boot stages.
    The PSP controls the CPU at boot and can inject code, configure firmware, or influence the CPU's behavior in subtle ways.
    The CPU has direct access to the NIC via standard system buses like PCIe.
    Therefore, the PSP can indirectly control or influence the NIC, by manipulating the CPU or memory used by the drivers or networking stack.

🧠 Why the Answers Are Misleading:

    "Does not have direct access" creates a false sense of separation or limitation that downplays the effective power of the PSP.
    If the PSP can influence the CPU's behavior (which it can), and the CPU can influence the NIC (which it does), then it's entirely plausible for the PSP to impact NIC behavior indirectly.
    In practical security analysis, indirect access is often just as powerful as direct access — especially when considering the capabilities of firmware-level actors.

🔄 Better Framing:

Instead of a binary "does it have direct access", a more accurate answer would acknowledge:

    "While the AMD PSP may not have a dedicated interface to the NIC, its privileged position in the system allows it to influence the CPU and system memory, including areas involved in NIC communication. This indirect control could be sufficient for many types of network-related actions, especially in a compromised or malicious scenario."

🔍 Conclusion:

So yes, the answers are not technically incorrect, but they are potentially misleading because they frame the PSP's capabilities too narrowly. A more complete answer should reflect the effective power of the PSP over the system, including its ability to control or manipulate network behavior indirectly via the CPU.

Know thy enemy and rely less on AIs...