Linux Security Hardening & Kernel Research

Linux powers the vast majority of the world's cloud infrastructure, embedded devices, and supercomputers. Consequently, its security posture is paramount. At Udero, we focus on dissecting the Linux kernel's security mechanisms to understand not just how to configure them, but why they work and where their boundaries lie.

Kernel Hardening Fundamentals

The Linux kernel is a complex beast, and its default configuration often prioritizes compatibility and performance over maximum security. Hardening involved reducing the attack surface by disabling unprivileged access to kernel structures and enabling mitigations against common exploit classes.

Key areas of focus include:

• Sysctl Tuning: Restricting access to dmesg (kernel.dmesg_restrict), hardening BPF (kernel.unprivileged_bpf_disabled), and tightening network stack parameters.
• Memory Protections: Understanding KASLR (Kernel Address Space Layout Randomization), SMEP/SMAP (Supervisor Mode Execution/Access Prevention), and how they mitigate ROP/JOP attacks.
• Module Loading: Enforcing module signing and disabling dynamic module loading in critical environments to prevent rootkits.

Linux Security Modules (LSMs)

Discretionary Access Control (DAC) — standard file permissions — is insufficient for modern threat models. Linux Security Modules (LSMs) provide the framework for Mandatory Access Control (MAC), enforcing policies that constrain even the root user.

SELinux

Security-Enhanced Linux (SELinux) uses a label-based system to enforce fine-grained type enforcement. It is robust but notoriously complex. We break down SELinux policies, booleans, and contexts to make it approachable for system administrators and developers.

AppArmor

AppArmor provides path-based MAC, often preferred for its ease of use. We explore creating profiles that effectively confine applications without breaking their functionality, analyzing audit logs to refine these profiles iteratively.

Isolation: Namespaces & Cgroups

The building blocks of containers are Linux Namespaces and Control Groups (cgroups).

• Namespaces: Provide resource isolation (PID, Network, Mount, UTS, IPC, User). We investigate the security implications of user namespaces and the risks of container breakouts.
• Cgroups: Manage resource allocation and metering. While primarily for performance, they play a role in preventing Denial of Service (DoS) attacks by limiting resource exhaustion.

Secure Boot & Integrity

Security must start at the boot chain. We analyze:

• UEFI Secure Boot: Ensuring only signed bootloaders and kernels are executed.
• IMA/EVM: The Integrity Measurement Architecture (IMA) and Extended Verification Module (EVM) provide runtime integrity checks, ensuring that files haven't been tampered with since they were signed.