Reverse tracing

Reverse tracing is the process of analyzing a program to understand which path in the code led to a particular state or action. This method is widely used in software debugging and vulnerability analysis, as well as in anti-cheat systems to detect manipulations with the game code or memory.

How Reverse Tracing Works

• State Capture: The initial stage involves capturing the state of the program at a specific point in time. This could be a particular point where an anomaly, unauthorized memory change, or suspicious API call is detected.
• Call Stack Analysis: Reverse tracing includes analyzing the program's call stack to identify the sequence of function calls that led to the current state. The call stack stores information about which functions were called and in what order, starting from the current function back to the program's entry point.
• Step-by-Step Debugging: Using debugging tools such as GDB (GNU Debugger) or WinDbg, a developer or anti-cheat system can step through the program's execution process, starting from the current state and moving backward through the function calls. This helps understand which changes were made and how.
• Register and Memory Analysis: During reverse tracing, CPU registers and the state of the operational memory can be analyzed to understand data changes and their source. This is especially useful for detecting code injections or the use of exploits.
• Identifying the Malicious Code: Reverse tracing helps identify specific areas of the code that were changed or used by a cheat. This can reveal where a third-party tool interfered with the normal execution of the program.

Application in Anti-Cheat Systems

In anti-cheat systems, reverse tracing can be used to:

1. Detect Injections and Modifications: Reverse tracing helps determine where an unexpected modification in memory or game code originated from, allowing the identification of the tool or method used.
2. Analyze Player Behavior: If a player exhibits unusual behavior (e.g., super-accurate aiming), the system can use reverse tracing to analyze the executed code and identify potential interference.
3. Debug Anti-Cheat Algorithms: Anti-cheat developers use reverse tracing to analyze and improve their detection algorithms, identifying unforeseen issues and enhancing detection accuracy.

Usage Example

Game Decompilation and Code Injection:

1. Initiation: The anti-cheat detects that data in the operational memory was modified at a specific point in time, which does not correspond to normal behavior.
2. Call Stack Capture: Reverse tracing is initiated, capturing all function calls performed up to the point where the anomaly was detected.
3. Analysis: The sequence of function calls and registers is analyzed. It is found that the code responsible for changing the data was injected from an external process.
4. Identifying the Culprit: Reverse tracing reveals that an external program injecting its code used a specific system call to make its changes.
5. Action: The anti-cheat can block the identified process, notify the player, and send information to the developers for further analysis and signature updates.

Reverse tracing is a powerful tool not only for software debugging but also for ensuring the security and integrity of gaming applications, allowing unauthorized interventions to be detected and blocked.