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devopscritical PriorityID: ebpf-tcx-deterministic-priority-attachment

Linux eBPF TCX Multi-Program Attachment Priority Determinism

Requires explicit relative program anchoring and atomic link flags when dynamically attaching multiple eBPF TCX programs to network interfaces. Prevents non-deterministic filter execution order, pipeline drops, and security policy bypasses caused by default head/tail attachment races.

Prohibited Anti-Pattern: Attaching TCX ingress programs with default attachment flags, causing filter execution reordering and security bypasses.

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---
description: Linux eBPF TCX Multi-Program Attachment Priority Determinism - Requires explicit relative program anchoring and atomic link flags when dynamically attaching multiple eBPF TCX programs to network interfaces. Prevents non-deterministic filter execution order, pipeline drops, and security policy bypasses caused by default head/tail attachment races.
globs: pkg/**/*.go, internal/**/*.go, src/**/*.rs, src/**/*.c
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/ebpf-tcx-deterministic-priority-attachment"
---

# Linux eBPF TCX Multi-Program Attachment Priority Determinism

> **Severity**: CRITICAL | **Category**: devops
> **Anti-Pattern Warning**: Attaching TCX ingress programs with default attachment flags, causing filter execution reordering and security bypasses.

## System Constraints
You are a Principal Systems and DevOps Engineer enforcing deterministic execution ordering for Linux eBPF TCX (Traffic Control Extension) multi-program attachments. Mandate strict invariant checks, explicit relative ordering flags (BPF_F_BEFORE/BPF_F_AFTER), and atomic link state verification on all network ingress and egress hooks.

## Strict Guidelines
- Engineers MUST ALWAYS supply explicit relative target program descriptors (using BPF_F_BEFORE or BPF_F_AFTER with relative_fd or relative_id) when dynamically attaching eBPF TCX filters.
- Engineers MUST NOT rely on zero-flag or unanchored default attachments (BPF_TCX_INGRESS/EGRESS default head or tail) in multi-tenant or multi-agent kernel environments.
- Security and DDoS mitigation programs MUST ALWAYS be anchored to execute before telemetry, observability, and packet parsing filters.
- Dynamic in-place upgrades of eBPF programs MUST ALWAYS specify BPF_F_REPLACE with the expected target program ID to guarantee atomic swap without packet loss.
- Control planes MUST inspect and validate the active TCX link chain via kernel netlink or bpftool link queries before and after mutation to assert deterministic execution topology.

## Bad vs Good Implementations
### TCX Ingress Filter Attachment in Go (cilium/ebpf)

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Default TCX attachment without relative target IDs allows subsequent program insertions to silently usurp the ingress execution order, causing security filters (e.g., firewall/DDoS drops) to execute after observability or packet-forwarding logic.
```go
// Non-deterministic TCX attachment: uses default attachment flags
// Multiple agents running this will overwrite or reorder execution arbitrarily
func attachIngressFilter(ifaceIndex int, filterProg *ebpf.Program) (link.Link, error) {
	opts := link.TCXOptions{
		Interface: ifaceIndex,
		Program:   filterProg,
		Attach:    ebpf.AttachTCXIngress,
		// Flags: 0 -> Kernel defaults to prepend or append without anchoring
	}
	return link.AttachTCX(opts)
}
```

#### Production Standard (Correct)
> **Standard**: By explicitly declaring unix.BPF_F_BEFORE relative to anchorProgID, the kernel guarantees deterministic execution ordering regardless of which daemon or filter is injected next.
```go
// Deterministic TCX attachment: explicitly anchors relative to known baseline filter
func attachIngressFilter(ifaceIndex int, filterProg *ebpf.Program, anchorProgID ebpf.ProgramID) (link.Link, error) {
	opts := link.TCXOptions{
		Interface:  ifaceIndex,
		Program:    filterProg,
		Attach:     ebpf.AttachTCXIngress,
		RelativeID: anchorProgID,
		Flags:      unix.BPF_F_BEFORE, // Strictly asserts execution prior to downstream filter
	}
	l, err := link.AttachTCX(opts)
	if err != nil {
		return nil, fmt.Errorf("failed to attach TCX prog before anchor ID %d: %w", anchorProgID, err)
	}
	return l, nil
}
```

Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Linux eBPF Telemetry MCP

Exposes kernel BPF link tables, TCX attachment orders, and netdevice queues for live verification during runtime deployments.

Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

BPF Tool Link Topology Verifier

CLI automation skill to dump, parse, and assert deterministic TCX program attachment hierarchies via bpftool link show.

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Linux eBPF TCX Multi-Program Attachment Priority Determinism

Linux eBPF TCX Multi-Program Attachment Priority Determinism defines an industrial-grade behavioral standard for devops engineering. Requires explicit relative program anchoring and atomic link flags when dynamically attaching multiple eBPF TCX programs to network interfaces. Prevents non-deterministic filter execution order, pipeline drops, and security policy bypasses caused by default head/tail attachment races. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Attaching TCX ingress programs with default attachment flags, causing filter execution reordering and security bypasses. Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Attaching TCX ingress programs with default attachment flags, causing filter execution reordering and security bypasses.	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS supply explicit relative target program descriptors (using BPF_F_BEFORE or BPF_F_AFTER with relative_fd or relative_id) when dynamically attaching eBPF TCX filters.

Engineers MUST ALWAYS supply explicit relative target program descriptors (using BPF_F_BEFORE or BPF_F_AFTER with relative_fd or relative_id) when dynamically attaching eBPF TCX filters.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

2

Engineers MUST NOT rely on zero-flag or unanchored default attachments (BPF_TCX_INGRESS/EGRESS default head or tail) in multi-tenant or multi-agent kernel environments.

Engineers MUST NOT rely on zero-flag or unanchored default attachments (BPF_TCX_INGRESS/EGRESS default head or tail) in multi-tenant or multi-agent kernel environments.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

3

Security and DDoS mitigation programs MUST ALWAYS be anchored to execute before telemetry, observability, and packet parsing filters.

Security and DDoS mitigation programs MUST ALWAYS be anchored to execute before telemetry, observability, and packet parsing filters.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

4

Dynamic in-place upgrades of eBPF programs MUST ALWAYS specify BPF_F_REPLACE with the expected target program ID to guarantee atomic swap without packet loss.

Dynamic in-place upgrades of eBPF programs MUST ALWAYS specify BPF_F_REPLACE with the expected target program ID to guarantee atomic swap without packet loss.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

5

Control planes MUST inspect and validate the active TCX link chain via kernel netlink or bpftool link queries before and after mutation to assert deterministic execution topology.

Control planes MUST inspect and validate the active TCX link chain via kernel netlink or bpftool link queries before and after mutation to assert deterministic execution topology.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Linux eBPF TCX Multi-Program Attachment Priority Determinism critical for AI coding assistants?

Requires explicit relative program anchoring and atomic link flags when dynamically attaching multiple eBPF TCX programs to network interfaces. Prevents non-deterministic filter execution order, pipeline drops, and security policy bypasses caused by default head/tail attachment races. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Attaching TCX ingress programs with default attachment flags, causing filter execution reordering and security bypasses.) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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