feat(cli): add native gVisor (runsc) sandboxing support

[Zheyuan-Lin]

Summary

This PR adds native support for gVisor (via runsc) as a sandboxing provider. Users on Linux can run Gemini CLI with stronger process isolation by leveraging gVisor's user-space kernel.
runsc is not auto-detected—it must be explicitly set (e.g. GEMINI_SANDBOX=runsc or sandbox: "runsc"). If you currently use Docker with custom args such as SANDBOX_FLAGS="--runtime=runsc", consider switching to the native runsc support instead.

Details

• Core type: Added runsc to the SandboxConfig command type union and VALID_SANDBOX_COMMANDS.
• Native support: When sandbox: "runsc" is set, the CLI runs docker run --runtime=runsc ...; no auto-detection—runsc is used only when explicitly configured.
• Runtime integration: Linux-only check at sandbox start; container command is derived from config while preserving config.command for env propagation.
• User reminder: When SANDBOX_FLAGS contains --runtime=runsc but the sandbox command is plain docker, the CLI logs a tip to use native runsc upport (sandbox: "runsc") instead.
• Documentation: Updated docs/cli/sandbox.md (setup, prerequisites, install/configure/verify) and README to state that runsc is not auto-detected.
• Tests: Added unit tests in packages/cli/src/config/sandboxConfig.test.ts and packages/cli/src/utils/sandbox.test.ts.

Related Issues

Fixes #15875

How to Validate

1. Build: npm run build
2. Sandbox tests:
   npx vitest run packages/cli/src/config/sandboxConfig.test.ts packages/cli/src/utils/sandbox.test.ts (or npm test -w @google/gemini-cli -- src/config/sandboxConfig.test.ts src/utils/sandbox.test.ts)
3. On Linux (with gVisor installed):
   • Run GEMINI_SANDBOX=runsc gemini "your prompt".
   • Confirm the CLI uses gVisor (e.g. debug logs show sandbox with
     --runtime=runsc in the spawn args).

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • macOS (npm run, npx, Docker, Podman, Seatbelt)
  • Windows (npm run, npx, Docker)
  • Linux (npm run, npx, Docker; runsc logic requires a Linux host)

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces native support for gVisor (runsc) as a sandboxing option within the Gemini CLI, enhancing process isolation for Linux users. By explicitly configuring runsc, users can leverage gVisor's user-space kernel for a more secure execution environment. The changes include core type updates, robust validation for platform and binary availability, and integration with Docker to utilize the runsc runtime. This feature provides a more streamlined and validated approach for gVisor users compared to manual configuration via SANDBOX_FLAGS.

Highlights

• Native gVisor (runsc) Sandboxing: Added native support for gVisor (runsc) as a sandboxing provider, offering stronger process isolation for Gemini CLI on Linux.
• Explicit Configuration: Implemented explicit configuration for runsc via GEMINI_SANDBOX=runsc or sandbox: "runsc", as it is not auto-detected.
• Docker Integration: Integrated runsc by internally executing docker run --runtime=runsc ... when specified.
• Validation Checks: Introduced validation checks to ensure runsc is used only on Linux and that both runsc and docker binaries are present.
• User Guidance: Provided a user tip in debug logs for those using SANDBOX_FLAGS="--runtime=runsc" with the docker sandbox command, suggesting a switch to native runsc support.
• Documentation and Tests: Updated documentation (docs/cli/sandbox.md) to include setup, prerequisites, and usage instructions for gVisor, and added comprehensive unit tests for runsc specific logic.

Changelog

• docs/cli/sandbox.md
  • Added a new section detailing gVisor/runsc sandboxing, including its benefits, prerequisites, and setup instructions.
  • Updated the GEMINI_SANDBOX environment variable options to include runsc.
• packages/cli/src/config/sandboxConfig.test.ts
  • Expanded sandbox command validation error messages to include runsc.
  • Added a new test suite for runsc sandboxing, covering configuration loading via CLI, environment variables, and settings files.
  • Included tests for platform-specific rejections (macOS, Windows) and missing binary errors (runsc or docker).
  • Verified that runsc is not auto-detected when sandbox: true.
• packages/cli/src/config/sandboxConfig.ts
  • Added runsc to the VALID_SANDBOX_COMMANDS array.
  • Implemented logic to check if runsc is selected on a Linux platform and if both runsc and docker binaries are available.
  • Modified the sandbox command detection to explicitly handle runsc and prevent its auto-detection.
• packages/cli/src/utils/sandbox.test.ts
  • Added tests to confirm that start_sandbox correctly uses docker with --runtime=runsc when runsc is configured.
  • Included tests for FatalSandboxError when runsc is attempted on non-Linux platforms.
  • Added a test to verify the debug log tip is displayed when SANDBOX_FLAGS contains --runtime=runsc with the docker command.
• packages/cli/src/utils/sandbox.ts
  • Introduced a command variable to resolve the actual executable (docker for runsc) for sandbox operations.
  • Added a platform check for runsc at the start of the start_sandbox function.
  • Modified ensureSandboxImageIsPresent and other execSync/spawn calls to use the resolved command.
  • Injected --runtime=runsc into Docker arguments when config.command is runsc.
  • Implemented a debug logger tip for users who specify --runtime=runsc in SANDBOX_FLAGS while using the docker sandbox command.
• packages/core/src/config/config.ts
  • Updated the SandboxConfig interface to include runsc as a valid type for the command property.

Activity

• The pull request was created by Zheyuan-Lin.
• No additional review comments or activity have been recorded yet.

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[gemini-code-assist]

Code Review

This pull request introduces native support for gVisor (runsc) sandboxing, which is a great enhancement for security on Linux systems. However, it contains a high-severity command injection vulnerability in the proxy container startup logic due to unsanitized string concatenation in a shell command, which should be addressed by using array-based argument passing for process spawning. Additionally, there is a suggestion to address code duplication in validation logic for improved maintainability, which is supported by the rule regarding trusting internally managed configurations.

[Zheyuan-Lin]

@scidomino PTAL

[scidomino]

This may take a while since I've never set up gvisor on my machine before.

[scidomino]

Thanks for the PR adding native gVisor sandboxing support! It looks great overall, especially the secure refactor of the proxy container spawn logic to use shell: false and an array of arguments—that's a fantastic improvement against command injection.

I have a couple of minor suggestions before we merge:

1. Remove the Migration Tip: The debugLogger is primarily for internal debugging (unless GEMINI_DEBUG=true is set), so normal users won't see the tip you added for migrating from SANDBOX_FLAGS=--runtime=runsc to sandbox: "runsc". I suggest removing this tip and the associated check entirely, as it adds a bit of complexity for a message that won't reach most users.

2. Redundant String Check (If kept): If you do decide to keep the tip (perhaps moving it to a user-facing output), note that the check f === '--runtime=runsc' || f.startsWith('--runtime=runsc') is slightly redundant, as startsWith already covers the exact match case.

Other than that, the platform checks, binary requirements, and test coverage look excellent. Please let me know if you have any questions!

[Zheyuan-Lin]

Hi @scidomino, thanks for the review! Removed the migration tip and relevant test cases. PTAL!

[dtometzki]

hello together,

but the main issue sandbox in vscode terminal doesnt work with runsc too. What i do wrong ?

[Zheyuan-Lin]

Hi @dtometzki, thanks for raising this!

You're not doing anything wrong — this is a known limitation when using GEMINI_SANDBOX=runsc. gVisor's network isolation prevents the IDE companion from establishing its TCP connection to the host, so the disconnection is expected behavior rather than a misconfiguration.

Recommended fix: Switch to Docker when you need IDE integration

Also worth noting — the error message you're seeing is unfortunately misleading. It's not an issue with your extension setup, but rather a known incompatibility between gVisor's network stack and the IDE connection mechanism. We should improve that message to make this clearer.