AMD pitfalls

Many of these are a few years out of date.

Nowadays there’s openSIL - it’s AMD’s attempt to provide some source code again, that projects like coreboot can use, but AMD is still problematic; the PSP for example (see below) cannot be “neutered” (nothing like me_cleaner, or psp_cleaner) exists yet.

AMD Platform Security Processor

This is basically AMD’s own version of the Intel Management Engine. It has all of the same basic security and freedom issues, although the implementation is wildly different.

The Platform Security Processor (PSP) is built in on the AMD CPUs whose architecture is Late Family 16h (Puma), Zen 17h or later (and also on the AMD GPUs which are GCN 5th gen (Vega) or later). On the CPUs, a PSP controls the main x86 core startup. PSP firmware is cryptographically signed with a strong key similar to the Intel ME. If the PSP firmware is not present, or if the AMD signing key is not present, the x86 cores will not be released from reset, rendering the system inoperable.

The PSP is an ARM core with TrustZone technology, built onto the main CPU die. As such, it has the ability to hide its own program code, scratch RAM, and any data it may have taken and stored from the lesser-privileged x86 system RAM (kernel encryption keys, login data, browsing history, keystrokes, who knows!). To make matters worse, the PSP theoretically has access to the entire system memory space (AMD either will not or cannot deny this, and it would seem to be required to allow the DRM “features” to work as intended), which means that it has at minimum MMIO-based access to the network controllers and any other PCI/PCIe peripherals installed on the system.

In theory any malicious entity with access to the AMD signing key would be able to install persistent malware that could not be eradicated without an external flasher and a known good PSP image. Furthermore, multiple security vulnerabilities have been demonstrated in AMD firmware in the past, and there is every reason to assume one or more zero day vulnerabilities are lurking in the PSP firmware. Given the extreme privilege level (ring -2 or ring -3) of the PSP, said vulnerabilities would have the ability to remotely monitor and control any PSP enabled machine completely outside of the user’s knowledge.

Much like with the Intel Boot Guard (an application of the Intel Management Engine), AMD’s PSP can also act as a tyrant by checking signatures on any boot firmware that you flash, making replacement boot firmware (e.g. libreboot, coreboot) impossible on some boards. Early anecdotal reports indicate that AMD’s boot guard counterpart will be used on most OEM hardware, disabled only on so-called “enthusiast” CPUs.

AMD IMC firmware

Read coreboot documentation on AMD IMC.

AMD SMU firmware

Handles some power management for PCIe devices (without this, your laptop will not work properly) and several other power management related features.

The firmware is signed, although on older AMD hardware it is a symmetric key, which means that with access to the key (if leaked) you could sign your own modified version and run it. Rudolf Marek (coreboot hacker) found out how to extract this key in this video demonstration, and based on this work, Damien Zammit (another coreboot hacker) partially replaced it with free firmware, but on the relevant system (ASUS F2A85-M) there were still other such files present (Video BIOS, and others).

AMD AGESA firmware

This is responsible for virtually all core hardware initialization on modern AMD systems. In 2011, AMD started cooperating with the coreboot project, releasing this as source code under a free license. In 2014, they stopped releasing source code and started releasing AGESA as vendor blobs instead. This makes AGESA now equivalent to Intel FSP.