The Art of Reverse Engineering: Demystifying the Stack [Part 16]

The stack is a fundamental concept in computer science and a critical component of reverse engineering. In this blog post, we will discuss what the stack is, how it works, and how it can be used in reverse engineering.

What is the stack?

The stack is a data structure that stores data in a last-in, first-out (LIFO) order. This means that the most recently added data is the first to be removed. The stack is used to store temporary data, such as function parameters and local variables.

How does the stack work?

The stack is implemented in hardware by the CPU. The CPU has a special register called the stack pointer (SP) that points to the top of the stack. When data is pushed onto the stack, the SP is decremented. When data is popped off the stack, the SP is incremented.

How can the stack be used in reverse engineering?

1. The stack can be used in reverse engineering to:
2. Analyze the flow of control in a program.
3. Identify function calls and returns.
4. Recover corrupted data.
5. Find buffer overflow vulnerabilities.

Example

Let's take a look at an example of how the stack can be used in reverse engineering. The following code shows a simple function that pushes two numbers onto the stack and then pops them off and prints them:

void foo(int a, int b) {

  int x = a;

  int y = b;

  push(x);

  push(y);

  x = pop();

  y = pop();

  printf("%d %d\n", x, y);

}

To analyze the flow of control in this function, we can use the stack to track the values of the variables x and y. When the function starts executing, the stack pointer will point to the top of the stack. The first instruction in the function pushes the value of a onto the stack. This will cause the stack pointer to be decremented by 4 bytes. The next instruction pushes the value of b onto the stack. This will cause the stack pointer to be decremented by another 4 bytes.

The next two instructions, x = pop() and y = pop(), pop the values off the stack and store them in the variables x and y. This will cause the stack pointer to be incremented by 8 bytes. The final instruction, printf("%d %d\n", x, y), prints the values of x and y.

By tracking the values of x and y on the stack, we can see that the function first pushes the values of a and b onto the stack. Then, it pops the values off the stack and stores them in x and y. Finally, it prints the values of x and y.

Conclusion

The stack is a powerful tool that can be used in reverse engineering. By understanding how the stack works, you can gain valuable insights into the flow of control in a program and identify potential vulnerabilities.

I hope this blog post has given you a better understanding of the stack in reverse engineering. If you have any questions, please feel free to leave a comment below.