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Add documentation for policy internals

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Describes changes in QubesOS/qubes-core-qrexec#30.
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Paweł Marczewski 2020-03-02 14:21:45 +01:00
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commit 1aacec4ab9
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2 changed files with 31 additions and 6 deletions
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6
developer/debugging/vm-interface.md
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@ -205,6 +205,12 @@ Other Qrexec services installed by default:
`qubes.VMExec+ls+--a+-2Fhome-2Fuser`
- `qubes.VMExecGUI` - a variant of `qubes.VMExec` that waits for full VM
startup first
Services called in GuiVM:
- `policy.Ask`, `policy.Notify` - confirmation prompt and notifications for
Qubes RPC calls, see [qrexec-policy implementation](/doc/qrexec-internals/#qrexec-policy-implementation)
for a detailed description.
Currently Qubes still calls few tools in VM directly, not using service
abstraction. This will change in the future. Those tools are:

31
developer/services/qrexec-internals.md
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@ -43,12 +43,6 @@ Command line usage:
* `domain-name`: Associated domain name.
* `default user`: Optional. If passed, `qrexec-daemon` uses this user as default for all execution requests that don't specify one.
### qrexec-policy
`/usr/bin/qrexec-policy`
Internal program used to evaluate the RPC policy and decide whether an RPC call should be allowed.
### qrexec-client
`/usr/bin/qrexec-client`
@ -229,3 +223,28 @@ Details of all possible use cases and the messages involved are described below.
Because the command is of the form `QUBESRPC ...`, `qrexec-fork-server` starts it using `qubes-rpc-multiplexer` program, which finds and executes the necessary script in `/etc/qubes-rpc/`.
- After that, the data is passed between **domX** and **domY** as in the previous examples (dom0-VM, VM-dom0).
## `qrexec-policy` implementation
`qrexec-policy` is a mechanism for evaluating whether an RPC call should be allowed. For introduction, see [Qubes RPC administration](/doc/qrexec/#qubes-rpc-administration).
### `qrexec-policy-daemon`
This is a service running in dom0. It is called by `qrexec-daemon` and is responsible for evaluating the request and possibly launching an action.
The daemon listens on a socket (`/var/run/qubes/policy.sock`). It accepts requests in the format described in [qrexec-policy-daemon.rst](https://github.com/QubesOS/qubes-core-qrexec/blob/master/Documentation/qrexec-policy-daemon.rst) and replies with `result=allow/deny`.
A standalone version is called `qrexec-policy-exec` and is available as a fallback.
### `qrexec-policy-agent`
This is a service running in the GuiVM. It is called by `qrexec-policy-daemon` in order to display prompts and notifications to the user.
It is a [socket-based Qubes RPC service](/doc/qrexec-socket-services/). Requests are in JSON format, and response is simple ASCII.
There are two endpoints:
- `policy.Ask` - ask the user about whether to execute a given action
- `policy.Notify` - notify the user about about an action.
See [qrexec-policy-agent.rst](https://github.com/QubesOS/qubes-core-qrexec/blob/master/Documentation/qrexec-policy-agent.rst) for protocol details.