Linux and Memory Corruption: Deep-Dive into Kernel Exploitation & Defense

Introduction to Virtual Memory Layout

Modern operating systems isolate processes in their own virtual address spaces. In 64-bit Linux architectures, memory is typically divided between user space and kernel space, preventing rogue user processes from corrupting fundamental system state.

Memory corruption bugs occur when a program writes data outside the memory boundaries allocated for a given buffer. The consequences range from benign segmentation faults to arbitrary kernel privilege escalation.

Memory safety is not just a language feature; it is an architectural contract between the compiler, operating system, and microarchitecture.

Buffer Overflows: The Classic Stack Vector

When an unbounded memory copy routine such as strcpy() or gets() operates on user-controlled inputs, excess bytes spill beyond the allocated stack frame, overwriting the saved frame pointer (RBP) and the saved instruction pointer (RIP).

// Vulnerable snippet demonstrating lack of bounds check
void handle_client_packet(const char *input, size_t len) {
    char stack_buf[256];
    // Dangerous: does not bound check against 256 bytes
    memcpy(stack_buf, input, len);
    process_payload(stack_buf);
}

Modern Mitigations: ASLR, Stack Canaries, and CFI

To combat these vectors, modern Linux kernels implement multiple defensive rings:

• Address Space Layout Randomization (ASLR): Randomizes the base addresses of stack, heap, and shared libraries on process execution.
• Stack Canaries: Compiler-injected random canary values placed immediately before the saved return address.
• Control Flow Integrity (CFI): Ensures forward and backward call transfers adhere to strict control flow graphs.

Understanding these defensive rings is essential for security researchers auditing systems for resilience.