Basics of eBPF

eBPF Overview

• Bytecode: eBPF programs begin as source code in a restricted subset of the C programming language. Specialized compilers like Clang can transform this source code into eBPF bytecode. The Linux kernel can optionally apply JIT (Just-In-Time) compilation to convert this bytecode into native machine instructions, thereby optimizing performance.
• Verifier: Before eBPF bytecode gets to execute in the kernel, it must pass a series of checks performed by a runtime verifier. This verifier ensures the absence of infinite loops and unauthorized memory access, thus providing a crucial safety net. It also checks for code terminations and type safety to ensure the code is well-behaved.
• Hook Points: eBPF programs can latch onto numerous types of events or ‘hooks’ within the Linux kernel. These hooks could range from XDP (eXpress Data Path) for intercepting and manipulating incoming network packets, tc (Traffic Control) for shaping and policing traffic, to tracepoints for generalized system observation.
• Helper Functions: The Linux kernel offers a set of predefined functions that eBPF programs can call to perform specific actions. These functions provide an interface to modify packet data, interact with BPF maps, or even emit trace and log data for debugging and monitoring.
• Maps: To maintain state or share data between the user-space and kernel-space, eBPF utilizes data structures known as BPF maps. These key-value stores are versatile and can be accessed and manipulated both from within the eBPF program and from user space through system calls.

Applications of eBPF

• Networking: Beyond basic packet filtering, eBPF allows for more complex logic, including custom load balancing algorithms and DDoS mitigation techniques.
• Monitoring: It can be employed to gather a wide array of system and network metrics, often with less overhead than traditional monitoring tools.
• Security: Custom security rules, policies, and data filtering can be implemented, thereby extending or fine-tuning the kernel’s built-in security mechanisms.
• Tracing and Profiling: eBPF provides a low-latency means of tracking system calls, function calls, and other significant system events, aiding in performance analysis and debugging.

Security Considerations

• Verifier Bypass: If the verifier has vulnerabilities, adversaries could potentially load malicious eBPF programs that execute arbitrary code within the kernel, leading to privilege escalation or data leakage.
• Resource Consumption: Malicious or poorly designed eBPF programs could consume excessive CPU or memory resources, making them a potential vector for DoS attacks.
• Data Leakage: Suboptimal eBPF programs can accidentally leak sensitive information through tracepoints, logs, or BPF maps.
• Unintended Side Effects: Carelessly or maliciously altered system states via eBPF could cause disruptions in system operations or invalidate existing security measures.
• Insufficient Isolation: Failing to isolate eBPF resources properly can allow one user’s eBPF programs to influence or interfere with another’s, opening a pathway for cross-user attacks or data corruption.

Adversarial Use Cases

• Information Gathering: A skilled adversary could use eBPF’s powerful data collection capabilities for in-depth system reconnaissance, thereby planning for more targeted and devastating attacks.
• Evasion: By altering system call parameters or network packet data, an adversary can use eBPF to thwart detection systems and monitoring tools.
• Persistence: Although challenging due to built-in security measures like the verifier, an adept adversary could potentially use eBPF to maintain a resilient foothold within a compromised system, making detection and removal difficult.