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Buffer Overflow Attacks in RISC-V: A Hands-On Lab Guide for CDA 4205L

Learn how buffer overflow vulnerabilities work in RISC-V assembly with this step-by-step tutorial for CDA 4205L Lab #13. Understand stack memory, overwrite passwords, and explore prevention techniques.

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Introduction

Buffer overflow attacks remain a critical security vulnerability in low-level programming. In this tutorial, we explore the concepts behind buffer overflow attacks in the context of the RISC-V instruction set architecture, as covered in CDA 4205L Lab #13. By understanding how memory is organized on the stack and how buffers can overflow, you'll gain insight into both the attack mechanism and the defensive coding practices that prevent it. This knowledge is especially relevant today as cybersecurity threats evolve, and even modern AI systems can be vulnerable to similar memory corruption issues.

Understanding the Stack and Buffers

In computer architecture, the stack is a region of memory used for storing local variables, return addresses, and saved registers. When you allocate a buffer on the stack, you reserve a contiguous block of memory. In RISC-V assembly, you manage the stack pointer (sp) manually. A buffer overflow occurs when you write more data to a buffer than its allocated size, overwriting adjacent memory locations.

Memory Layout Example

Consider a program that declares an 8-byte input buffer followed by an 8-byte password buffer in the data segment. In memory, these are adjacent:

Address  Content
0x1000   InputBuffer[0..7]
0x1008   Password[0..7]

If you write 16 bytes of input, the second half overwrites the password. This is the core of a buffer overflow attack.

The Lab Scenario: Simulating an Attack in RISC-V

In CDA 4205L Lab #13, you are given a RISC-V assembly program that simulates a password check. The correct password is "cda4205L". Your goal is to bypass authentication by overflowing the input buffer.

Step-by-Step Attack

  1. Download and run the buffer_overflow.asm file from Canvas. Compile and execute it. A dialog box prompts for a password.
  2. Enter the correct password (cda4205L) – access granted.
  3. Enter an incorrect password (e.g., cda3201) – access denied.
  4. Observe the data memory view. Check the ASCII box to see stored characters. You'll see your input and the correct password stored in adjacent memory.
  5. Overflow the buffer: Enter a string of repeating characters like "aaaa...a" (more than 8 characters). Watch in the memory view as your input overwrites the password location.
  6. Repeat until access is granted – when your input completely overwrites the password with the same pattern, the comparison succeeds.

Key Questions

  • T1: How many characters to reach the password? How many to overwrite it? (Answer: 8 to reach, 16 to overwrite both buffers.)
  • T2: Screenshot the console output showing access with an incorrect password.
  • T3: How to prevent? Use bounds checking or a safer input function like fgets that limits input length.

Real-World Relevance: From Gaming to AI

Buffer overflows are not just academic; they appear in video game exploits, AI model vulnerabilities, and even finance apps. For example, a buffer overflow in an online game's chat system could allow arbitrary code execution. In AI systems, malformed inputs can cause memory corruption in inference engines. Understanding these attacks helps you write secure code in low-level programming and system security.

Defensive Coding Practices

Modern compilers use stack canaries, ASLR, and non-executable stacks to mitigate overflows. As a programmer, you should:

  • Always check buffer sizes before writing.
  • Use safe functions like strncpy instead of strcpy.
  • In assembly, explicitly check input length against allocated space.

Conclusion

Buffer overflow attacks exploit the lack of bounds checking in low-level languages. By understanding the RISC-V memory model and practicing with this lab, you develop a hacker mindset that is essential for cybersecurity and ethical hacking. Apply these principles to protect your own code from memory corruption vulnerabilities.