This article provides a comprehensive overview of Linux rootkit theory, tracing their evolution from early user-space shared object (SO) techniques to advanced kernel-level implants. It explores the core components of rootkits—loaders and payloads—and explains how these stealthy tools manipulate the operating system to conceal files, processes, and network connections. By examining the lifecycle and architecture of these threats, the text establishes a foundation for understanding how attackers maintain long-term, undetected access to high-value infrastructure.
The technical deep dive covers various hooking techniques used to subvert the Linux kernel, including legacy methods like IDT and syscall table hijacking, alongside modern approaches like ftrace-based hooking and inline patching. It specifically addresses recent architectural changes in Linux kernel 6.9+ that render traditional syscall table patching ineffective, while introducing emerging evasion strategies utilizing eBPF and io_uring. This analysis highlights the constant adaptation of rootkit designs in response to hardening kernel defenses and improved monitoring capabilities.
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