Executing a firmware binary

Executing a firmware binary requires emulating or replicating the environment in which the binary was designed to run. Firmware binaries are often tightly coupled to specific hardware, so executing them directly on a general-purpose computer can be challenging. Below are the steps and methods to execute and analyze a firmware binary:

Steps to Perform Binary Execution

1. Analyze the Binary Format

• Use tools like file or binwalk to determine the firmware’s structure.
• Check for:
  • The architecture (e.g., ARM, MIPS, x86).
  • The format (e.g., ELF, raw binary, compressed).
• Example: file firmware.bin binwalk firmware.bin

2. Extract or Decompress the Firmware

• If the binary is part of a compressed archive or filesystem:
  • Use binwalk with extraction flags: binwalk -e firmware.bin
  • Identify and extract embedded filesystems (e.g., SquashFS, JFFS2).

3. Set Up an Emulator

• Firmware binaries are usually built for specific architectures, so you’ll need to emulate the appropriate hardware environment. Common emulators include:
  • QEMU: Supports multiple architectures like ARM, MIPS, x86, and more. qemu-system-ARCH -kernel firmware.bin
  • GDB: Debug and analyze the binary in a controlled environment.
• Identify the entry point or startup code using tools like Ghidra, Radare2, or IDA Pro.

4. Load the Binary in an Emulator

• Use the firmware’s architecture and peripheral configuration to set up QEMU or another emulator.
• For example, for an ARM-based binary: qemu-system-arm -M versatilepb -kernel firmware.bin -nographic

5. Simulate the Peripherals (Optional)

• Firmware often interacts with hardware peripherals like GPIO, I2C, or UART.
• Use tools like Peripheral Emulator Framework (PEF) to simulate hardware peripherals.

6. Run the Firmware in a Sandbox

• If you extracted the firmware’s filesystem:
  • Use chroot to simulate the environment: sudo chroot ./extracted_rootfs /bin/bash
  • Use QEMU user mode to execute binaries within the extracted filesystem: qemu-arm-static ./extracted_rootfs/bin/binary

7. Debug and Trace the Execution

• Attach a debugger like GDB to analyze the binary execution: gdb-multiarch -q firmware.elf
• Use dynamic analysis tools like:
  • strace: To trace system calls.
  • ltrace: To trace library calls.

Advanced Methods

1. Firmware-Specific Platforms

• Use specialized platforms like:
  • UNIFUZZ: For fuzzing embedded firmware.
  • Avatar²: To dynamically analyze firmware with emulated and real hardware.

2. Hardware Testing

• If emulation is not feasible, load the firmware onto the original device or a similar testbed device.

3. Recompile or Port the Firmware

• If the binary format allows it, modify the code and recompile it for your native platform.

Challenges and Mitigation

Hardware Dependencies

• Firmware binaries often rely on specific hardware peripherals.
• Mitigation: Simulate peripherals or bypass hardware-specific code using patching.

Encryption

• Firmware may be encrypted or obfuscated.
• Mitigation: Decrypt or reverse-engineer the encryption mechanism.

Unsupported Architectures

• The binary architecture may not be supported by the tools you have.
• Mitigation: Install the required architecture support in QEMU or other emulators.

Tools for Binary Execution

1. Binwalk: Analyze and extract firmware files.
2. QEMU: Emulator for various architectures.
3. GDB: Debugging firmware binaries.
4. Ghidra/IDA Pro: Static analysis and reverse engineering.
5. Firmadyne: Firmware analysis framework for Linux-based firmware.
6. Unicorn Engine: Lightweight CPU emulator for dynamic binary analysis.