GHIDRA is a powerful software reverse engineering tool that can analyze binaries from various architectures and platforms. However, sometimes GHIDRA does not support a specific format or device out of the box, and you need to write your own loader to make it work. In this article, we will show you how to write a GHIDRA loader for STM32 microcontrollers, which are widely used in embedded systems and IoT devices.
STM32 microcontrollers use the ARM Cortex-M core, which is supported by GHIDRA. However, they also have a specific memory layout and flash programming algorithm that GHIDRA does not recognize by default. To write a GHIDRA loader for STM32, we need to do the following steps:
Create a new project in GHIDRA and import the binary file that we want to analyze.
Write a Java class that implements the Loader interface and overrides the load method.
Register the loader class in the loaders.lcs file in the ghidra/Ghidra/Features/Base/data directory.
Restart GHIDRA and select our custom loader when importing the binary file.
Use the GHIDRA API to map the memory regions, set the processor type, and load the symbols from the binary file.
Analyze the binary file using GHIDRA's features and tools.
In the following sections, we will explain each step in more detail and provide some code snippets to illustrate the process.
Create a new project and import the binary file
The first step is to create a new project in GHIDRA and import the binary file that we want to analyze. The binary file can be obtained from the STM32 device using a debugger or a flash programmer tool. For this example, we will use a binary file from an STM32F103C8T6 microcontroller, which has 64 KB of flash memory and 20 KB of RAM. The binary file contains a simple LED blinking program that toggles the state of an LED connected to pin PC13 every second.
To create a new project in GHIDRA, we need to launch GHIDRA and select File -> New Project. Then we need to choose a name and a location for the project, and select Non-Shared Project. After creating the project, we need to import the binary file by selecting File -> Import File. Then we need to browse to the location of the binary file and select it. At this point, GHIDRA will ask us to choose a loader for the file. We will see that there is no loader for STM32 available by default, so we need to write our own.
Write a Java class that implements the Loader interface
The next step is to write a Java class that implements the Loader interface and overrides the load method. The Loader interface defines how GHIDRA should load a binary file into its internal data structures. The load method takes four parameters: a String representing the name of the file, an Object representing the provider of the file data, a LoadSpec representing the specification of how to load the file, and a List<DomainObject> representing the list of domain objects that will be created by loading the file. The method returns a List<Message>, which contains any messages or errors that occurred during loading.
To write our custom loader class, we need to create a new Java project in an IDE of our choice (such as Eclipse or IntelliJ IDEA) and add the ghidra.jar file as a dependency. The ghidra.jar file can be found in the ghidra/Ghidra/Features/Base/lib directory. Then we need to create a new Java class named STM32Loader.java, which implements