Munition (Chimichanga)

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A capability attenuation framework for sandboxed WASM execution in Elixir.

Overview

Munition provides secure execution of untrusted WebAssembly code with three core guarantees:

Guarantee	Description
Bounded Execution	Fuel-metered computation that guarantees termination. Every WASM instruction consumes fuel; exhaustion halts execution deterministically.
Memory Isolation	Each execution gets fresh, isolated linear memory. No state leaks between executions.
Forensic Capture	Failure state is automatically captured for post-mortem analysis. Memory snapshots, fuel state, and execution context preserved atomically.

The Capability Attenuation Model

Munition implements a formal model for capability attenuation across language boundaries:

┌─────────────────┐     ┌─────────────────┐     ┌─────────────────┐
│  Source Code    │     │   Attenuator    │     │    Runtime      │
│  (rich caps)    │ ──▶ │   (compiler)    │ ──▶ │  (restricted)   │
│                 │     │                 │     │                 │
│  PHP: can do    │     │  Removes/maps   │     │  WASM: can only │
│  anything       │     │  capabilities   │     │  do what host   │
│                 │     │                 │     │  permits        │
│  Pony: typed    │     │  Preserves      │     │                 │
│  capabilities   │     │  proofs         │     │  Elixir: super- │
│                 │     │                 │     │  vises, captures│
└─────────────────┘     └─────────────────┘     └─────────────────┘

Attenuation Strategies

Strategy	Source Languages	Description
Restrictive	PHP, JavaScript	Source has implicit universal capabilities. Attenuator removes/intercepts all capability exercise.
Preserving	Pony	Source has typed capabilities. Attenuator maps source capabilities to target capabilities.
Additive	Rust	Source already has ownership guarantees. Runtime adds additional isolation (fuel, memory bounds).

Architecture

Component Overview

┌────────────────────────────────────────────────────────────────────┐
│                           Public API                               │
│                         Munition.fire/4                            │
└─────────────────────────────────┬──────────────────────────────────┘
                                  │
┌─────────────────────────────────▼──────────────────────────────────┐
│                       Instance Manager                             │
│                   Munition.Instance.Manager                        │
│                                                                    │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────────────────┐ │
│  │   Compile    │→ │ Instantiate  │→ │       Execute            │ │
│  └──────────────┘  └──────────────┘  └──────────────────────────┘ │
│          │                │                      │                 │
│          ▼                ▼                      ▼                 │
│  ┌──────────────────────────────────────────────────────────────┐ │
│  │                    Forensic Capture                          │ │
│  │                 (on any failure path)                        │ │
│  └──────────────────────────────────────────────────────────────┘ │
└─────────────────────────────────┬──────────────────────────────────┘
                                  │
┌─────────────────────────────────▼──────────────────────────────────┐
│                      Runtime Behaviour                             │
│                     Munition.Runtime                               │
│                                                                    │
│  ┌────────────────────┐  ┌────────────────────┐                   │
│  │  Wasmex (default)  │  │  (future runtimes) │                   │
│  │   via Wasmtime     │  │                    │                   │
│  └────────────────────┘  └────────────────────┘                   │
└────────────────────────────────────────────────────────────────────┘

Module Structure

Module	Responsibility
lib/munition.ex	Public API: fire/4, fire_pooled/4, validate/2
lib/munition/instance/manager.ex	Lifecycle orchestration: compile → instantiate → execute → capture → cleanup
lib/munition/instance/state.ex	Instance lifecycle state tracking
lib/munition/runtime/behaviour.ex	Pluggable WASM engine interface
lib/munition/runtime/wasmex.ex	Wasmtime implementation via Wasmex
lib/munition/forensics/dump.ex	Structured crash dump format with MNTN serialization
lib/munition/forensics/capture.ex	Atomic state capture on failure
lib/munition/forensics/analyser.ex	Memory introspection and pattern searching
lib/munition/fuel/policy.ex	Default fuel allocations and complexity calculation
lib/munition/fuel/meter.ex	Consumption tracking and statistics
lib/munition/host/functions.ex	Host function registry with capability gating
lib/munition/host/capabilities.ex	Capability definitions and validation

Quick Start

Installation

# Add to mix.exs
{:munition, "~> 0.1.0"}

Basic Usage

wasm = File.read!("plugin.wasm")

case Munition.fire(wasm, "process", [input], fuel: 100_000) do
  {:ok, result, metadata} ->
    IO.puts("Result: #{inspect(result)}")
    IO.puts("Fuel remaining: #{metadata.fuel_remaining}")

  {:crash, :fuel_exhausted, forensics} ->
    IO.puts("Execution exceeded fuel limit")
    IO.puts(Munition.Forensics.Dump.summary(forensics))

  {:crash, :trap, forensics} ->
    IO.puts("WASM trap occurred")
    analyser = Munition.Forensics.Analyser.new(forensics)
    IO.puts(Munition.Forensics.Analyser.hex_dump(analyser, 0, 256))
end

Features in Action

Fuel Metering (Guaranteed Termination)

# This will ALWAYS terminate - no infinite loops possible
{:crash, :fuel_exhausted, _} =
  Munition.fire(wasm, "infinite_loop", [], fuel: 1_000)

Memory Isolation

# Execution A writes to memory
Munition.fire(wasm, "write_data", [pattern])

# Execution B cannot see it - fresh memory every time
{:ok, [0], _} = Munition.fire(wasm, "read_data", [0])

Forensic Capture

{:crash, reason, forensics} = Munition.fire(wasm, "buggy_function", [])

# Serialize for offline analysis
binary = Munition.Forensics.Dump.serialize(forensics)
File.write!("crash_dump.mntn", binary)

# Extract insights
analyser = Munition.Forensics.Analyser.new(forensics)
strings = Munition.Forensics.Analyser.extract_strings(analyser)

Formal Specification

Munition includes a formal TLA+ specification proving capability safety, termination, and forensic capture guarantees. See Capability Model for:

• Formal definitions (Source Language, Target Runtime, Attenuator)

• Soundness and Completeness properties

• Forensic Capture specification

• Full TLA+ model

• Soundness proof sketch

Security Guarantees

Property	Guarantee
Termination	Fuel exhaustion guarantees all executions terminate
Memory Safety	WASM linear memory is bounds-checked
Isolation	No shared state between executions
Capability Restriction	Only explicitly granted capabilities are accessible
Forensic Preservation	All failures are captured atomically for audit

Non-Guarantees

• Execution time is bounded but not constant (timing side-channels possible)

• CPU cache timing attacks remain possible

• Memory allocation before instantiation may exhaust host resources

• Custom host functions must be implemented securely

Development

Prerequisites

• Elixir 1.14+

• Rust (for building test WASM modules)

• just (task runner)

Setup

git clone https://github.com/hyperpolymath/chimichanga
cd chimichanga

# Full setup (deps + WASM)
just setup

# Or manually:
mix deps.get
cd test_wasm && cargo build --target wasm32-unknown-unknown --release
mkdir -p test/fixtures
cp test_wasm/target/wasm32-unknown-unknown/release/munition_test_wasm.wasm test/fixtures/test.wasm

Testing

just test              # All tests
just test-unit         # Unit tests only (no WASM required)
just test-integration  # Integration tests only
just test-coverage     # With coverage report

Code Quality

just check             # Run all checks (fmt, lint, dialyzer)
just lint              # Credo analysis
just dialyzer          # Type checking
just validate          # Full RSR Gold validation

Project Statistics

Metric	Value
Elixir Source	~1,955 lines (14 modules)
Test Suite	~380 lines (unit + integration)
Test WASM (Rust)	~286 lines
Documentation	40+ KB across 14 files
Version	0.1.0 (pre-release)
RSR Compliance	Gold

Documentation

• Architecture - System design and execution flows

• Capability Model - Formal specification and proofs

• Contributing - Tri-Perimeter Contribution Framework

• Governance - Decision-making model

• Security - Vulnerability reporting policy

• Reversibility - Safe operations commitment

• Roadmap - Future development plans

License

Dual-licensed under MIT OR AGPL-3.0-or-later.

See LICENSE.txt for details.

Maintainers

See MAINTAINERS.md for the current maintainer list.

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Maintained by Hyperpolymath