Baremetal Rasberry Pi Zero CTF Challenges

Motivation

• Develop unique CTF Challenges
• Give myself a challenge
• Realistic view of how ARM is used in microcontrollers

Key Differences (from reversing Linux binaries)

• No Operating System 
  • No Security Features
  • No File System
  • No Heap (needs to be implemented)
  • Code + Data in same memory section
     
• No Standard Libraries by Default
   
• No Symbols/Not an ELF file
   
• No Virtual Memory by Default

What that means for Developers?

Really, really weird things...

Malloc Implenetation Example

Linux Implementation

• https://code.woboq.org/userspace/glibc/malloc/malloc.c.html
• Over 5500 lines to ensure that it is writing in heap correctly
• Virtual Memory

What that means for Exploiters/Reverse Engineers? 

Resources

• https://github.com/bztsrc/raspi3-tutorial
  • Learning Baremetal Firmware Development
     
• https://medium.com/codex/reverse-engineering-bare-metal-low-level-kernel-images-with-qemu-getting-started-c705b7b14d35
  • Full Walkthrough of Solving Furor
     
• https://ctftime.org/writeup/27578