👉 Overview
👀 What ?
Seccomp, or Secure Computing Mode, is a Linux kernel feature that provides a means of limiting the system calls a process can make. It is a crucial component of sandboxing applications for increased security, and it helps in reducing the attack surface of the Linux kernel.
🧐 Why ?
Seccomp is important because it provides a mechanism for system administrators and developers to increase the security of a system. By limiting the system calls a process can make, it reduces the potential avenues of attack, making it harder for an attacker to exploit vulnerabilities in a program or in the kernel itself. For readers who are responsible for maintaining the security of Linux systems, understanding and effectively implementing Seccomp can be a significant safeguard against potential cyber threats.
⛏️ How ?
To use Seccomp, one must first identify the minimal set of system calls required by an application, and then create a Seccomp filter that only allows these calls and denies all others. This filter is then applied to the application using the prctl() or seccomp() system call. Because this process requires a deep understanding of the application's operation and the system calls it makes, it may be challenging for beginners. However, tools such as 'strace' can be used to trace the system calls made by an application, making it easier to create an appropriate Seccomp filter.
⏳ When ?
The use of Seccomp became more widespread with the release of Linux kernel 3.5 in July 2012, which introduced 'Seccomp-BPF', a much more flexible and practical version of Seccomp that allows for fine-grained control over system call filtering.
⚙️ Technical Explanations
Seccomp operates by examining the system call number just before a system call is made. The system call number, along with its arguments, are available in CPU registers. Seccomp uses a 'Berkeley Packet Filter' (BPF) program to decide whether to allow or deny the system call. If the BPF program returns 'allow', the system call proceeds as normal. If it returns 'deny', the process is terminated. This method of operation has the advantage of minimal performance overhead, as the BPF program is run in the kernel and does not require a context switch.