Use the Ghidra Language Definition in this Pull Request: https://github.com/NationalSecurityAgency/ghidra/pull/1147 - it works for the rpi-eeprom images and using ghidra is a much better approach than using the results in this repository. Thanks @mumbel

Raspberry Pi 4 Bootloader Analysis

This repository contains my "processed" disassembly of the contents of the Raspberry Pi4 bootloader. This is the contents of the rpi-eeprom package, and the files are available on Github here.

I disassembled the various rpi-eeprom.bin files using vc4-toolchain. I also referenced an open-source project that aim{s,ed} for a libre firmware that can be flashed in place of the stock firmware. I referenced this firmware to get an understanding of the load addresses and some of the important memory locations, as well as to try to figure out when the VC4 code starts up the ARM core(s). rpi-open-firmware targets Raspberry Pi 3, meaning its a replacement for bootcode.bin and not rpi-eeprom.bin. Thus, there are surely some differences in the implementation that I am simply not aware of. I'll think about looking at bootcode.bin and doing some comparative analysis between it and rpi-eeprom.bin. Duplicates have been removed, in case you see some files that are in rpi-eeprom but not in this project.

Great?

The disassembly files have some super basic, fairly crappy "analysis" applied to them. Basically I wrote some scripts that compare the strings output to the objdump output and try to match things up. It is definitely prone to error and inaccuracy, but I was aiming for best effort. I also attempted to mark where addresses are branched from with the BREF annotation. This repository contains the original disassembly (*.disassembly.bin) as well as my mapped disassembly (*.map.bin) so you can reference both of them if you want to do some analysis.

Why?

I built these disassembly files and applied my "analysis" to them to help guide me in reverse engineering the RPi4 bootloader. I want to:

• Understand how the bootloader works, especially the new Secure Boot capabilities and the networking capabilities.
• Manually diff the various versions of the rpi-eeprom.bin releases to identify fixes from the release notes. This is a precursor for identifying silently patched security issues.
• Find new security issues, particularly in the Secure Boot capabilities and the networking capabilities.

This seems like a really bad solution?

You're right! The real solution is a Ghidra SLEIGH language definition so we can do real reverse engineering. I unfortunately cannot make the time commitment right now to learn both the ins and the outs of the VC4 assembly language (assuming enough details exist to even feasibly attempt to write a Ghidra language definition) and the process by which to create a new Ghidra language definition. If that wasn't enough, on top of that I'm just not very smart.

Your python and shell scripts are terribly written

Yep.

How can I learn VC4 assembly language?

You can start by reading everything in this wiki entry.

Can I Contribute?

Yes.

How?

Some of the STRING and XREF annotations in the *.map.txt files are invalid. Feel free to remove some of those from the results if you want and submit a PR. Also if you could update the scripts to ensure that a given false positive will not happen again, that would be swell.

Also, please do not create issues saying some part of my annotations are incorrect. If you know they are incorrect and it bothers you enough to want to create an issue, please just submit a pull request fixing the annotation.