Standalone Policy Prover

openshell-prover checks whether the authority in a local candidate policy is contained within a local boundary policy. The command reads files from the host and does not connect to an OpenShell gateway.

The candidate must be the fully composed effective policy after the proposed change, including any provider-contributed authority. The boundary is an operator-owned ceiling. It does not grant authority by itself.

Install the Prover

The standard OpenShell installer includes openshell-prover:

curl -LsSf https://raw.githubusercontent.com/NVIDIA/OpenShell/main/install.sh | sh
openshell-prover --version

The prover remains independent of the gateway at runtime. If you only need the standalone binary, use the artifacts listed in the Support Matrix. These artifacts and openshell-prover-checksums-sha256.txt are attached to OpenShell releases.

The release archive includes the solver linkage required by the executable. It does not require the main openshell command, a gateway configuration, or a separate Z3 installation.

Check a Policy Boundary

Create boundary.yaml with this boundary policy:

version: 1
filesystem_policy:
  read_only:
    - /usr
    - /etc

Create candidate.yaml with this contained candidate:

version: 1
filesystem_policy:
  read_only:
    - /usr

Run the check:

openshell-prover check candidate.yaml --boundary boundary.yaml

A contained candidate prints result: within_boundary and exits with status 0. To see an exceeding result and its counterexample, replace candidate.yaml with a policy that grants writes to /tmp. The boundary grants no write access:

version: 1
filesystem_policy:
  read_only:
    - /usr
  read_write:
    - /tmp

openshell-prover check candidate.yaml --boundary boundary.yaml

To check the current effective policy of an existing sandbox, export it without display metadata:

openshell sandbox get my-sandbox --policy-only > candidate.yaml
openshell-prover check candidate.yaml --boundary boundary.yaml

This export includes provider-contributed rules. For a proposed change that is not active, supply the complete post-change effective policy. The standalone prover does not compose a base policy with provider rules.

Use JSON when a script consumes the result:

openshell-prover check candidate.yaml \
  --boundary boundary.yaml \
  --output json

The JSON object includes the result, exit code, input paths, prover version, model version, checked policy version, and modeled domains. The documented semantics and environmental conditions for that scope are tied to its model version. An exceeding result also includes a filesystem or network counterexample. Automation should use result and reason_code instead of parsing the human-readable explanation.

The stable reason codes are invalid_input, unsupported_policy_shape, unresolved_workdir, unresolved_binary_path, unresolved_filesystem_path, solver_timeout, solver_unknown, resource_limit, invalid_witness, and cancelled.

The solver has a finite 10-second default budget. Set a different positive budget with an integer followed by ms, s, or m:

openshell-prover check candidate.yaml \
  --boundary boundary.yaml \
  --timeout 30s \
  --output json

Exit Codes

Only exit 0 means the verification succeeded. Treat unsupported and inconclusive results as failures in CI.

Interpretation and Limits

The initial containment model covers filesystem paths, L4 network authority, and enforced REST method and path authority, including explicit REST denies. The result object reports the domains used for each check. Policies that use recognized authority outside that model return unsupported rather than silently ignoring it.

Both inputs use the same bounded YAML/JSON parser and authored policy schema as OpenShell. Unknown fields, duplicate keys, malformed field types, and unsupported managed metadata or review annotations return error with reason_code: invalid_input and exit 2. Schema-valid controls outside the containment model return unsupported and exit 3.

The prover applies aggregate limits across the candidate and boundary before semantic shape validation: 1,024 network rules, 4,096 endpoints, 4,096 binary selectors, 65,536 authored port entries, 16,384 REST rules, 4 KiB per modeled pattern, and 1 MiB of modeled pattern text. Exceeding any limit returns inconclusive with reason_code: resource_limit. A cancellation already requested at preflight takes precedence over that result; otherwise a resource limit takes precedence over unsupported policy-shape diagnostics. This ordering keeps validation work bounded for checked-in CI inputs.

Network binary selectors, endpoint host and path selectors, and REST allow and deny method and path selectors must use ASCII literals in both the candidate and boundary. A non-ASCII literal in one of these fields returns unsupported with reason_code: unsupported_policy_shape, including when it appears only in a deny. Embedded NUL bytes in these fields are also unsupported. This is a prover-model limitation, not a general policy validation rule: filesystem paths and unrelated policy text retain their existing Unicode behavior. ASCII wildcard selectors still cover non-ASCII runtime values matched by the policy engine.

Containment means Allowed(candidate) is a subset of Allowed(boundary) under the reported model. It does not establish least privilege, automatic approval eligibility, semantic safety, or equivalence to a running sandbox’s kernel state. In particular:

• The command does not fetch the current sandbox policy or compose provider rules. The caller must supply the effective candidate.
• The command does not apply, approve, or persist a policy.
• Environment-dependent authority, such as an unresolved image workdir, returns unsupported when the result depends on that missing context.
• Binary comparisons that can change when an image resolves an exact selector through a symlink return unsupported. This covers exact candidate grants under boundary globs and exact boundary denies replaced by candidate globs. Use matching exact canonical paths when possible.
• Policies with overlapping L4 and enforced REST endpoints return unsupported because inspection selection depends on the complete set of matching runtime endpoint configurations.
• Network containment checks both supported runtime configurations: binary identity enforcement enabled and disabled. When enabled, grants and denies match the executable or an ancestor identity. Network counterexamples report the configuration and identities that expose the additional authority.
• REST containment witnesses use canonical request methods and paths.
• If a solver string cannot be decoded and validated faithfully, the command returns inconclusive with reason_code: invalid_witness instead of emitting a counterexample.
• Both files are interpreted in the same sandbox filesystem namespace and mount model, with stable path resolution when enforcement rules are created. The CLI does not resolve sandbox paths against the host.
• Filesystem containment supports removing grants and reducing write grants to read-only grants at matching paths. A boundary grant for / also covers other paths for the same access. Comparisons between different paths otherwise return unsupported with reason_code: unresolved_filesystem_path: a lexical child can resolve outside its parent through a symlink, and unrelated paths can resolve to the same object. This includes narrowing /tmp to /tmp/cache. If the boundary grants no access of the requested kind, adding that access returns exceeds_boundary.

Use the Policy Schema Reference for the full policy language. A successful prover result covers only the scope reported in its evidence.