eBPF Kernel Helper Testing with Verifier-Safe Grammar Fuzzing

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Solution Overview

Problem

There is a need for automated testing of interfaces between extended Berkeley Packet Filter (eBPF) programs and the Linux OS kernel, which is not adequately addressed by existing techniques such as kernel fuzzing and BPF verifier/JIT compiler security methods.

Innovation Solution

A method is provided for testing OS kernel interfaces by receiving eBPF code configured to invoke and test the kernel interface using a fuzzing engine, generating kernel events to trigger the eBPF code, and recording arguments passed to the kernel through a shared data structure, ensuring that only events caused by user space code are reacted to.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If kernel fuzzing is used to test eBPF kernel interfaces, then automated testing coverage is improved, but the eBPF verifier security constraints are violated

Engineering Contradiction:

Improveautomated testing coverageVSAvoideBPF verifier security constraints

Core Design Contradiction:

Extent of automationVSReliability

Solution Approach 1:

The patent introduces a user-space intermediary layer that acts as a mediator between the fuzzing engine and the eBPF kernel interface. This intermediary generates valid eBPF programs according to the kernel interface grammar and handles the communication protocol, allowing automated fuzzing while maintaining verifier security constraints. The intermediary transforms fuzzing inputs into compliant eBPF bytecode that passes verification.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the parameter space of the fuzzing process by introducing grammar-based constraints on eBPF program structure. Instead of random fuzzing, the system uses grammar parsing to generate valid eBPF programs with proper syntax and semantics, ensuring they pass verifier inspections while still providing comprehensive testing coverage.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If eBPF programs are allowed to access kernel internals through new interfaces, then functionality and versatility are improved, but security and threat vectors are worsened

Engineering Contradiction:

ImproveeBPF kernel interface functionalityVSAvoidsecurity threat vectors

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary verification actions before eBPF programs can access kernel interfaces. The verifier performs preliminary checks on eBPF program semantics and the kernel interface grammar to ensure safety before allowing execution. This preliminary action prevents harmful code from reaching the kernel while maintaining full functionality of authorized interfaces.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback mechanisms where the kernel interface grammar provides feedback on valid argument structures, and the verifier provides feedback on program safety. This feedback loop allows the system to maintain security constraints while enabling versatile kernel access through continuous validation of eBPF programs against defined interfaces.

Inventive Principle:

Principle #23Feedback

3Speed

If eBPF filters are made asynchronous to improve performance, then execution speed is improved, but testability and code coverage are worsened

Engineering Contradiction:

ImproveeBPF execution speedVSAvoidcode coverage measurement

Core Design Contradiction:

SpeedVSDifficulty of detecting and measuring

Solution Approach 1:

The patent introduces user-space code as an intermediary that synchronizes with asynchronous eBPF execution. This intermediary generates kernel events that trigger eBPF programs and collects results, providing a synchronization mechanism that maintains async performance while enabling comprehensive testing and code coverage measurement through the shared data structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If the eBPF verifier is made strict to ensure security, then safety is improved, but ease of development and testing is worsened

Engineering Contradiction:

ImproveeBPF program safetyVSAvoideBPF program development and testing

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the development parameters by introducing grammar-based templates for eBPF program generation. These templates encode the kernel interface grammar and verification rules, allowing developers to generate verified programs automatically without manually crafting complex eBPF bytecode. This maintains strict verification while significantly easing development and testing.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12346453B2Automated testing of operating system (OS) kernel helper functions accessible through extended BPF (EBPF) filters

Publication Date: 2025.07.01 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method to test an OS kernel interface, such as an eBPF helper function. The interface has a grammar that defines the kernel interface. Testing is carried out using eBPF code that invokes and tests the interface using a fuzzing engine. To facilitate the process, additional user space code is configured to generate at least one kernel event that triggers the eBPF code to run, and to transform inputs from the fuzzing engine according to the grammar that defines the kernel interface. After loading the eBPF code into the OS kernel, the user space code issues the kernel event that causes the eBPF code to run. In response, and as the fuzzing engine executes, the eBPF code records arguments sent to the OS kernel through the kernel interface. The arguments are passed through a data structure shared by the eBPF code and the user space code. By recording the arguments and other diagnostic information, the security of the kernel interface is evaluated.