Securing the Serverless OS: Lightweight Kernel Hardening for Function-as-a-Service

Serverless computing, particularly Function-as-a-Service (FaaS), offers significant advantages in terms of scalability and cost-effectiveness. However, the shared nature of the underlying infrastructure raises security concerns. Hardening the serverless operating system (OS) kernel is crucial to mitigating these risks. This post explores lightweight kernel hardening techniques specifically tailored for FaaS environments.

Understanding the Serverless Security Landscape

FaaS platforms abstract away much of the infrastructure management, but this abstraction doesn’t eliminate security responsibilities. Security vulnerabilities in the underlying OS kernel can expose all functions running on that platform. Traditional kernel hardening techniques, often used for dedicated servers, might be too heavyweight for the ephemeral nature of FaaS.

Key Vulnerabilities to Address

• Kernel Exploits: Exploiting kernel vulnerabilities can grant attackers root privileges, enabling data breaches, denial-of-service attacks, and even control over other functions sharing the same kernel.
• Privilege Escalation: Even with secure functions, a compromised function could attempt to escalate privileges to access sensitive resources or other functions.
• Side-Channel Attacks: Functions might inadvertently leak information through side channels, like timing or power consumption.

Lightweight Kernel Hardening Techniques

The goal is to implement security enhancements without significantly impacting performance. Here are some practical approaches:

1. Minimal Kernel Modules

Load only absolutely necessary kernel modules. Unnecessary modules increase the attack surface. A streamlined kernel reduces the potential for vulnerabilities.

# Example (Linux):  List loaded modules
lsmod

# Example (Linux):  Remove unnecessary modules (requires root privileges)
modprobe -r <module_name>

2. Secure Boot and Measured Boot

Enable Secure Boot to ensure only trusted bootloaders and kernels are loaded. Measured Boot allows verifying the integrity of the boot process, detecting tampering attempts.

3. Kernel Address Space Layout Randomization (KASLR)

KASLR randomizes the location of kernel data structures in memory, making it more difficult for attackers to exploit memory corruption vulnerabilities.

# Example (Linux):  Check KASLR status (may require root privileges)
cat /proc/sys/kernel/randomize_va_space

4. Regular Kernel Updates

Keeping the kernel up-to-date is paramount. Patches addressing known vulnerabilities should be applied promptly. This is crucial for mitigating zero-day exploits.

5. Runtime Application Self-Protection (RASP)

RASP solutions monitor function execution for malicious activities. They can detect and prevent attacks in real-time, even if kernel vulnerabilities exist. This adds an extra layer of security.

Conclusion

Securing the serverless OS kernel is essential for building robust and secure FaaS applications. Lightweight kernel hardening, focusing on minimal modules, secure boot, KASLR, and regular updates, complemented by RASP solutions, provides a layered security approach that balances performance and protection. Choosing a reputable FaaS provider with a strong security posture and actively participating in security best practices are equally important aspects of a comprehensive security strategy.