Qubes OS infrastructure configuration
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README.md

Qubes OS build infrastructure configuration

This repository contains part of Qubes OS infrastructure configuration.

build-infra formula

This formula provides setup for Qubes OS build machine. It can consists of multiple build environments, each of them have at least two VMs:

  • build-ENV_NAME
  • keys-ENV_NAME

In addition to those, build-logs VM is created. Configuration allows:

  • build VM to upload build logs to build-logs VM
  • build-logs VM to unlock signing keys usage for appropriate keys VM
  • build VM access the keys VM

Each build VM have access to the network through Whonix Gateway, so all 3rd-party sources are downloaded through Tor.

Build environments list can be specified with build-infra:build-envs pillar. Example pillar is provided in /srv/pillar/base/qubesos-infra/build-infra.sls.

Usage:

  1. Enable this formula with:

     qubesctl top.enable build-infra
     qubesctl top.enable build-infra pillar=True
    
  2. Apply the configuration:

     qubesctl --all state.highstate
    
  3. Provision gpg signing keys into appropriate keys- VMs, setup qubes-builder in appropriate build- VMs. See below for detailed list.

build-infra.ssh-proxy formula

Configure ssh in build VMs to bypass Whonix Gateway. The main reason here is performance. This shouldn't affect main goal of using Tor - making targeted attacks harder, for attacker controlling 3rd-party signing key. Ssh is used only to:

  • download our code from github (where it's authenticated using gpg)
  • upload binary packages to appropriate repositories

Technically it's done by configuring ssh (ProxyCommand in ~/.ssh/config) to use local.ConnectSSH service to sys-net (and pass destination hostname in service argument), instead of establishing TCP connection directly. local.ConnectSSH service is implemented as simple netcat.

Usage:

  1. Enable this formula:

     qubesctl top.enable build-infra.ssh-proxy
    
  2. Apply the configuration:

     qubesctl --all state.highstate
    

Detailed description of the infrastructure

Build infrastructure consists of several build environments. Each of them use 3 VMs:

  1. Build VM (build-*), responsible for:
  • building the package with logging to build-logs VM in real time
  • sending build artifacts to Keys VM for signing (using split gpg)
  • uploading signed packages to repository
  • sending notifications to github (issue comments etc)
  1. Keys VM (keys-*), responsible for:
  • keeping signing keys
  • signing packages, but only if build-logs VM acknowledged build log reception
  1. Build logs VM (build-logs), common for all build environments, responsible for:
  • receiving build logs
  • sending them (in form of signed commits) to build-logs repository
  • signaling appropriate Keys VM of successful logs reception and sending

The above workflow and used qrexec services can be illustrated with the diagram below:

      .-----------.                     .----------.
      | build VM  |                     | keys VM  |
      |           |     4. qubes.Gpg    |          |
      |           |-------------------->|          |
      |           |                     |          |
      |           |                     |          |
      |           |                     '----------'
      '-----------'                              ^
            |                                    |
            |1. qubesbuilder.BuildLog            |
            |                                    |
            v                                    |
    .---------------. 3. qubesbuilder.LogReceived|
    | build-logs VM |----------------------------'
    |               |                         .-,(  ),-.    
    |               | 2. push signed logs  .-(          )-. 
    |               |********************>(     github     )
    |               |                      '-(          ).-'
    |               |                          '-.( ).-'    
    '---------------'

The build process may be triggered manually (be calling appropriate make command in some of build VM), or in response to github notification. The later is achieved using builder-github, which provide webhooks and qrexec services to handle this process. It boils down to:

  1. HTTP server in sys-net (nginx) receive HTTP POST request from github with information about an event in repository. It is handed to appropriate handler script from github-webhooks directory of builder-github.
  2. Webhook handler extract essential data (for example repository name) and send it to all build VMs using qubesbuilder.TriggerBuild qrexec service.
  3. Qrexec service in a build VM check if the named component exists in any of qubes-builder instance and call scripts/auto-build build script. This script check if anything new needs to be built - and if so, build it and upload to current-testing repository. This, among other things, report successful (or failed) build as an issue in appropriate repository.

Very similar approach is used to move packages from current-testing to current repository:

  1. HTTP server in sys-net (nginx) receive HTTP POST request from github with information about an comment on issue. It is handed to appropriate handler script from github-webhooks directory of builder-github.

  2. Webhook handler extract commend body, check if it have any PGP-signed data (but do not verify it yet) and send it to all build VMs using qubesbuilder.ProcessGithubCommand qrexec service.

  3. Qrexec service in a build VM check signature on the commend and if it's made by a trusted key, process the command. See documentation in builder-github for details.

            .-,(  ),-.                     .------------.
         .-(          )-.    HTTP POST     | sys-net    |
        (     github     )****************>|            |
         '-(          ).-'                 |            |
             '-.( ).-'                     '------------'
                 ^                                |
                 *                 qubesbuilder.TriggerBuild
        github issue/comment       qubesbuilder.ProcessGithubCommand
                 *                                |
                 *          .----------.          |
                 ***********| build VM |<---------|
                 *          '----------'          |
                 *                                |
                 *          .----------.          |
                 ***********| build VM |<---------'
                 *          '----------'
                 *
              packages
                 *
                 v
            .-,(  ),-.
         .-(          )-.
        (   repository   )
         '-(          ).-'
             '-.( ).-'
    

In addition to the above, build VM use Tor to download 3rd-party software (including build dependencies etc). This is to make targeted attack as hard as possible even for someone having write access to 3rd-party source/binary repository (including access to a signing key).

The above architecture is designed to make the build process as transparent as possible, while limiting damages of a compromised single build environment. Especially:

  • Build VM doesn't have direct access to a signing key, so it's impossible to leak it from there.
  • Packages signed with different keys are built in separate build environments. This means separate build environments for:
    • Fedora packages,
    • Debian packages,
    • Community-supported templates,
    • Contributed packages (TBD),
  • Build VM send build logs in real time - so even if the build environment would be compromised in the build process, it won't be able to erase the evidences from the build log. Note that after build VM is compromised, one can no longer trust further build logs, as those can be easily falsified. But those produced in the past (including the exact compromise incident) should remain immutable.
  • Build VM can request package signing only when sent a build log first. It's important to stress out here that Keys VM have no way to verify if the build log really corresponds to the binary received for signing. But since every build is logged in real time and it's a requirement for having package signed, logs will be available (publicly) and can be audited.

Post installation steps

Configuration tasks not included in this formula:

  1. In each keys VM:

    • generate/import appropriate signing key
  2. In each build VM:

    • generate/import ssh key used to upload packages

    • set username in .ssh/config for host where packages are uploaded (yum.qubes-os.org, deb.qubes-os.org etc)

    • populate .ssh/known_hosts for example by logging into updates server and verifying fingerprint

    • clone (and verify signed tag!) qubes-builder into directories listed in ~/.config/qubes-builder-github/builders.list

    • setup builder.conf in each instance, based on appropriate config in release-configs/. In most cases it's enough to create a symlink. When creating new config, make sure to:

      • drop NO_SIGN ?= 1 line
      • adjust DISTS_VM and DIST_DOM0 if needed (must be set using ?= operator)
      • adjust COMPONENTS, add builder-github there (must be set using ?= operator, cannot use +=)
      • set SIGN_KEY to appropriate key id (the one in matching keys VM)
      • set LINUX_REPO_BASEDIR to a appropriate directory (pointing exact release version, like $(SRC_DIR)/linux-yum/r4.0)
      • include $(HOME)/builder-github.conf
  3. In build-logs VM:

  • generate/import ssh key, add it to QubesOS/build-logs repository as deploy key with write access
  • import logs signing key
  1. Make sure build VMs are large enough.