qusal/docs/DESIGN.md

Design

Qusal design document.

Table of Contents

• Goal
• Documentation
• Format
  • Readme
  • File naming
  • State ID
  • Qube preferences
    • Qube naming
    • Qube label
    • Qube menu
  • Qube features
  • Qube connections
  • Qrexec call and policy
  • Qrexec socket services
• Browser isolation from the managed service

Goal

Provide a minimal modular isolated environment for users to complete daily tasks in a secure manner. We should not focus on a specific Qubes OS user base as it would narrow our reach. We scope to have a diverse user base, with different needs and use case that could shape our project for the better.

We must not aim to be a one solution fits all by adding every new project someone asks for, if the number of projects grows too large, it would be impossible to keep track of everything, especially with major distribution updates from templates and Qubes OS releases.

In order to achieve this goal, the formulas must always create qubes based on minimal templates, with only the strictly necessary packages and features it needs. If audio is not required, it is never installed and the qube preference audiovm is set to None, the same applies to networking, thus avoiding unexpected calls to the network or to the audio qube. If the memory requirements are low, it is capped to a low limit, thus avoiding exacerbated memory consumption on systems with low specs.

No extraneous features should be included by default besides the basic for functionality. Extra functionalities that could weaken the system can be provided via extra states that needs to be installed per the user discretion.

Documentation

Markdown code must follow Google's Markdown style guide. Any discrepancies with Google's style guide must be fixed or documented here with clear motive.

Documentation must not duplicate itself, but reference one another. Reproducing instructions that can be found in upstream documentation is discouraged unless the benefits of documenting it in-house, such as getting the documentation from a single source, do outweigh the necessity of having to modify the documentation constantly to keep up with upstream.

Format

Readme

Every project should have a README.md with at least the following sections:

• Table of Contents;
• Description;
• Installation;
• Access Control (if Qrexec policy changed);
• Usage; and
• Credits (if sourced).

Access Control

• It must document default policy and RPC services the user can or should edit.
• It must not document RPC services of other formulas unless the resolution of the rule is deny.

State file naming

1. Every State file .sls must have a Top file .top. This ensures that every state can be applied with top.
2. Every project must have a init.top, it facilitates applying every state by enabling a single top file.
3. State file naming must be common between the projects, it helps understand the project as if it was any other.
4. File name must use - as separator, not _ (unless it is required by the language, such as python).

State ID

1. State IDs must use - as separator, not _. The underline is allowed in case the features it is changing has underline, such as default_netvm.
2. State IDs must always have the project ID, thus allowing to target multiple states to the same minion from different projects without having conflicting IDs.

Qube preferences

Qube naming

We differ from upstream especially by placing the dvm part as the prefix of DispVM Templates. This is to easy parsing when the qube type is the first part of its name and no exceptions.

• TemplateVM: tpl-NAME
• StandaloneVM: NAME
• AppVM: NAME
• DispVM: disp-NAME
• DispVM Template (AppVM): dvm-NAME
• Service qubes (not a class): sys-NAME

We recommend that for user created qubes, use the domain in the prefix of the qube. An AppVM for personal banking will be named personal-banking, an AppVM for personal e-mail will be named personal-email.

Qube label

We differ from upstream in many senses. We are not labeling qubes based on them sharing a common security domain, this is very limited if you have many security domains in use and they do not share the same level of trust. You don't (or shouldn't) trust your networked browsing qube for personal usage the same as you trust your vault. The following method tries to fix this problem, domain name is in the prefix of the qube, the label is solely related to trustworthiness of the data it is dealing with.

• Black:
  • Trust: Ultimate.
  • Description: You must trust Dom0, Templates, Vaults, Management qubes, these qubes control your system and hold valuable information.
  • Examples: dom0, tpl-ssh, vault, dvm-mgmt.
• Gray:
  • Trust: Fully.
  • Description: Trusted storage with extra RPC services that allow certain operations to be made by the client and executed on the server or may build components for other qubes.
  • Examples: sys-cacher, sys-git, sys-pgp, sys-ssh-agent, qubes-builder.
• Purple:
• Trust: Very much.
• Description: Has the ability to manager remote servers via encrypted connections and depend on authorization provided by another qube. Examples: ansible, dev, ssh, terraform.
• Blue:
• Trust: Much.
• Description: TODO
• Examples: TODO
• Green:
  • Trust: Trusted.
  • Description: TODO
  • Examples: TODO
• Yellow:
  • Trust: Relatively trusted.
  • Description: TODO
  • Examples: TODO
• Orange:
  • Trust: Slight.
  • Description: Controls the network flow of data to the client, normally a firewall.
  • Examples: sys-firewall, sys-vpn, sys-pihole.
• Red:
  • Trust: Untrusted.
  • Description: Holds untrusted data (PCI devices, untrusted programs, disposables for opening untrusted files or web pages).
  • Examples: sys-net, sys-usb, dvm-browser.

Qube menu

The Qubes App Menu is used by GUI users, always add the .desktop files to the qube feature menu-items, if it is a template, also add to the feature default-menu-items. Remember to sync the App Menus after the installation of software in the desired qube.

Explicitly setting menu item avoids the user clicking on a software not intended to be run in the selected qube or trying to run software that is not installed. The user opening Tor Browser in a Whonix qube that is intended for building software is risky, the user trying to open a file manager on a qube that doesn't have one is less risky but for the user the behavior is unexpected.

Qube features

Control daemons using Qubes Services. It is much better to control services this way as we can declare during the creation of qubes instead of having to add a state to run a script during boot to unmask and start a specific service. The method below is most of the times combined with systemd.unit ConditionPathExists= to enable the service conditionally.

• Server's service name must match the syntax: service-server (example: rsync-server, syncthing-server);
• Client's service name must match the syntax: service-client (example: ssh-client;
• Local program's service name must match the syntax: service (example: docker, podman.

Qube connections

There are several ways a qube can connect to another, either directly with Xen or with Qrexec. If something is not required, we remove it.

• template is always required:
  • When required, must be set to the custom-made template;
  • When not possible to use, prefer StandaloneVMs instead.
• audiovm is rarely required on the majority of the projects:
• When required, set it to "*default*" to honor the global preferences.
• When not required, must be set to None;
• netvm is required on a lot of projects.
• When required, must not be managed to honor the global preferences. If it requires a custom networking scheme, the state must make sure that the netvm exists;
• When not required, must be set to None.
• default_dispvm is nice to have:
• When required, must guarantee that the network follows the same chain as the calling qube in the default configuration;
• When not required, must be set to None.
• management_dispvm is always required:
• When required, should not be managed to honor the global preferences, but it can make sense to set a custom management qube for debugging.
• When not required, such as on qubes that don't work through Salt, don't touch it, it doesn't increase attack surface.

Qrexec call and policy

1. Must not use * for source and destination, use @anyvm instead
2. Target qube for policies must be @default. It allows for the real target to be set by Dom0 via the target= redirection parameter, instead of having to modify the client to target a different server via qrexec-client-vm.
3. Target qube for client script must default to @default, but other targets must be allowed via parameters.

Qrexec socket services

Native Qrexec TCP sockets /dev/tcp using qubes.ConnectTCP are very handy to connect to a port of a qube. The downside of using qubes.ConnectTCP directly is the user doesn't want or need to know in which port the client wants to connect in the server. We will refer to Unix Domains Sockets as UDS.

Using qusal.Service, such as qusal.Rsync, qusal.Syncthing, qusal.Ssh has the following advantages:

• Usability: User recognizes the call per service name;
• Extensibility: Allows extending functionality for arguments added in the future, no need to migrate user policy from qubes.ConnectTCP; is not necessary;

Rules for server RPC service:

• Symlink qubes.ConnectTCP to qusal.Service if connecting to a local port;
• Use qubes.ConnectTCP directly when the user won't manage the policy for the wanted call, such as sys-syncthing-browser, where it happens that only this qube will access the admin interface of sys-syncthing;
• Use socat to connect to remote hosts or UDS with path defined by the service argument.

Rules for client RPC call:

• Use systemd.socket units, it does not require socat, it is not restricted to the use of qubes.ConnectTCP called by qvm-connect-tcp, the service can be properly logged and status verified by a service manager instead of forking socat to the background with a rc.local script and finally, can be controlled by Qubes Services to enable or disable the unit with ConditionPathExists= instead of doing if-else statements in rc.local;
• Use of socat and qvm-connect-tcp is permitted for UDS and for instructional use as it is very short.

Browser isolation from the managed service

Some projects have daemons and can be managed through a browser. The CLI is not suitable for everybody and sometimes it can be incomplete on GUI focused applications. Implement browser separation from the server to avoid browsing malicious sites and exposing the browser to direct network on the same machine the server is running. The browser qube is offline and only has access to the admin interface. In other words, it has control over the server functions, if the browser is compromised, it can compromise the server.

Some projects that uses this enhancement are sys-pihole, sys-syncthing and sys-cacher.