WIP

An audio qube acts as a secure handler for potentially malicious audio devices, preventing them from coming into contact with dom0 (which could otherwise be fatal to the security of the whole system). It thereby mitigates some of the security risks of using USB devices and Bluetooth devices. Nonetheless, we strongly recommend carefully reading the security warning on USB input devices devices before proceeding.

With an audio qube, many kinds of devices can be used (that previously were either unsafe or impossible to use in dom0):

Manual setup

In this section, we will explain how to manually set up an audio qube. A lot of alternatives configurations are also possible.

Creating the qubes

  1. Create a template named ‘audio-template’ – You can clone ‘fedora-XX’ template for that –
  2. Then create an appvm named ‘audio-app’ and mark it as a disposablevm template
  3. Finally, create a disposablevm named ‘sys-audio’

Note: By making "sys-audio" disposable, volume configuration will not be persistent.

See below, some screenshot of this configuration

audiovm-manager.png

audiovm-sysaudio-1.png

[details="Result of qvm-prefs audio-app"] 

audiovm               D  sys-audio
autostart             D  False
backup_timestamp      -  1689304025
debug                 D  False
default_dispvm        D  fedora-dvm
default_user          D  user
dns                   D  
gateway               D  
gateway6              D  
guivm                 D  dom0
icon                  D  templatevm-gray
include_in_backups    D  True
installed_by_rpm      D  False
ip                    D  
ip6                   D  
kernel                D  6.4.8-1.fc37
kernelopts            D  swiotlb=2048
keyboard_layout       D  fr+oss+
klass                 D  AppVM
label                 -  gray
mac                   D  00:16:3e:5e:6c:00
management_dispvm     D  default-mgmt-dvm
maxmem                D  4000
memory                D  400
name                  -  audio-app
netvm                 -  None
provides_network      -  False
qid                   -  50
qrexec_timeout        D  60
shutdown_timeout      D  60
start_time            D  
stubdom_mem           U
stubdom_xid           D  -1
template              -  audio-template
template_for_dispvms  -  True
updateable            D  False
uuid                  -  62ad295e-cfdc-4cbd-a5a7-09284dff87d9
vcpus                 D  2
virt_mode             D  pvh
visible_gateway       D  
visible_gateway6      D  
visible_ip            D  
visible_ip6           D  
visible_netmask       D  
xid                   D  -1
[/details]

[details="Result of qvm-prefs audio-template"] 

audiovm             D  sys-audio
autostart           D  False
backup_timestamp    -  1689304024
debug               D  False
default_dispvm      D  fedora-dvm
default_user        D  user
dns                 D  
gateway             D  
gateway6            D  
guivm               D  dom0
icon                D  templatevm-black
include_in_backups  D  True
installed_by_rpm    D  False
ip                  D  
ip6                 D  
kernel              D  6.4.8-1.fc37
kernelopts          D  swiotlb=2048
keyboard_layout     D  fr+oss+
klass               D  TemplateVM
label               -  black
mac                 D  00:16:3e:5e:6c:00
management_dispvm   D  default-mgmt-dvm
maxmem              D  4000
memory              D  400
name                -  audio-template
netvm               D  None
provides_network    D  False
qid                 -  49
qrexec_timeout      D  60
shutdown_timeout    D  60
start_time          D  
stubdom_mem         U
stubdom_xid         D  -1
updateable          D  True
uuid                -  43dfeca9-41b6-4b85-b462-2c566cc5da1f
vcpus               D  2
virt_mode           D  pvh
visible_gateway     D  
visible_gateway6    D  
visible_ip          D  
visible_ip6         D  
visible_netmask     D  
xid                 D  -1
[/details]

[details="Result of qvm-prefs sys-audio"] 

audiovm             D  sys-audio
auto_cleanup        D  False
autostart           -  True
backup_timestamp    -  1689304025
debug               D  False
default_dispvm      D  audio-app
default_user        D  user
dispid              -  2229
dns                 D  
gateway             D  
gateway6            D  
guivm               D  dom0
icon                D  dispvm-gray
include_in_backups  D  True
installed_by_rpm    D  False
ip                  D  
ip6                 D  
kernel              D  6.4.8-1.fc37
kernelopts          D  
keyboard_layout     D  fr+oss+
klass               D  DispVM
label               -  gray
mac                 D  00:16:3e:5e:6c:00
management_dispvm   D  default-mgmt-dvm
maxmem              -  0
memory              D  400
name                -  sys-audio
netvm               -  None
provides_network    -  False
qid                 -  51
qrexec_timeout      D  60
shutdown_timeout    D  60
start_time          D  1693413928.06
stubdom_mem         U
stubdom_xid         D  2
template            -  audio-app
updateable          D  False
uuid                -  9422a856-7b81-464d-9fd5-987ef2cf99f7
vcpus               D  2
virt_mode           -  hvm
visible_gateway     D  
visible_gateway6    D  
visible_ip          D  
visible_ip6         D  
visible_netmask     D  
xid                 D  1
[/details]

Installing the required packages

In ‘audio-template’, install the required packages: 

sudo dnf install -y alsa-plugins-pulseaudio alsa-utils pulseaudio-qubes pulseaudio-utils pipewire-utils qubes-audio-daemon pavucontrol xfce4-pulseaudio-plugin webrtc-audio-processing qubes-core-admin-client qubes-usb-proxy

Note: You could need to first remove the package ‘pipewire-pulseaudio’ before installing the other packages.

If you want to be able to use Bluetooth devices, you also need to install the following packages: 

sudo dnf install -y blueman pulseaudio-module-bluetooth cairo-dock

And the required drivers for your Bluetooth hardware, for example, some hardware will need this package:

sudo dnf install -y linux-firmware

Configuring PCI passthrough

Then we need to passthrough the PCI devices we want to ‘sys-audio’. It needs to be configured as HVM, without memory balancing.

audiovm-sysaudio-2.png

audiovm-sysaudio-3.png

Configuring sys-audio as the default audiovm

In dom0 execute the following command: 

qubes-prefs default_audiovm sys-audio

Testing sound

Note: qubes that were running before the moment the audiovm has started will not have sound. See Troubleshooting section.

Now you can check that sound can be played in ‘sys-audio’ by executing the following command in ‘sys-audio’.

aplay /usr/share/sounds/alsa/Noise.wav

In the screenshot below, I passed my audio jack device to ‘sys-audio’. The name of these devices are different on every hardware.

audiovm-devices|612x435

Note: You could permanently assign a usb device to a qube using the dom0 command qvm-devices. Example : qvm-devices usb attach --persistent sys-audio sys-usb-1:2-6

You can check what hardware is available using ‘pavucontrol’:

audiovm-pavu-1.png

audiovm-pavu-2.png

See the ‘Troubleshooting’ part if you have trouble with USB audio devices.

Bluetooth configuration

Nothing specific to QubesOS to configure your Bluetooth device, so the explanation will be minimal.

  1. In ‘sys-audio’ launch ‘blueman-manager’
  2. Pair with your Bluetooth hardware
  3. Activate the audio profiles

When you configure a Bluetooth device, the configuration files are stored as root in /var/lib/bluetooth. If you want the device to be permanently known by the audiovm (even after reboot), you need to either copy this folder to the template qube, or have any other means of deploying back the configuration that have been saved to /var/lib/bluetooth

Configuring services

Add the custom service ‘audiovm’ using QubesManager for your audio qube.

audiovm-sysaudio-4.png

Adding this service will launch at startup the following command:

qvm-start-daemon --all --watch

Configuring policy

Finally, we need to create a policy file to allow the required communications between ‘sys-audio’ and the other qubes. In dom0, create the file ‘/etc/qubes/policy.d/50-sys-audio.policy’ with the following content:

[details="Recommended way - patching source code required"] 

admin.Events          *   sys-audio     @adminvm                allow   target=dom0
admin.Events          +domain-stopped    sys-audio     @tag:audiovm-sys-audio                allow   target=dom0
admin.Events          +domain-shutdown   sys-audio     @tag:audiovm-sys-audio                allow   target=dom0
admin.Events          +domain-start  sys-audio     @tag:audiovm-sys-audio                allow   target=dom0
admin.Events          +connection-established      sys-audio     @tag:audiovm-sys-audio                allow   target=dom0

admin.vm.CurrentState *   sys-audio     @adminvm                allow   target=dom0
admin.vm.CurrentState *   sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.List         *   sys-audio     @adminvm                allow   target=dom0
admin.vm.List         *   sys-audio     @tag:audiovm-sys-audio  allow   target=dom0

admin.vm.property.Get               +audiovm      sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.property.Get               +xid          sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.feature.CheckWithTemplate  +audio        sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.feature.CheckWithTemplate  +audio-model  sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.property.Get               +stubdom_xid  sys-audio @tag:audiovm-sys-audio  allow   target=dom0

You additionally need to apply this patch: https://github.com/QubesOS/qubes-core-admin-client/compare/main...neowutran:qubes-core-admin-client:fix-8109-and-further [/details]

[details="Non recommended way - Giving much more permission than theorically needed"] 

admin.Events          *   sys-audio     sys-audio               allow   target=dom0
admin.Events          *   sys-audio     @adminvm                allow   target=dom0
admin.Events          *   sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.CurrentState *   sys-audio     sys-audio               allow   target=dom0
admin.vm.CurrentState *   sys-audio     @adminvm                allow   target=dom0
admin.vm.CurrentState *   sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.List         *   sys-audio     sys-audio               allow   target=dom0
admin.vm.List         *   sys-audio     @adminvm                allow   target=dom0
admin.vm.List         *   sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.property.Get               +audiovm sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.property.Get               +xid     sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.feature.CheckWithTemplate  +audio   sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.feature.CheckWithTemplate  +audio-model   sys-audio     @tag:audiovm-sys-audio  allow   target=dom0
admin.vm.property.GetAll * sys-audio    sys-audio   allow   target=dom0
admin.vm.property.GetAll * sys-audio    @tag:audiovm-sys-audio  allow   target=dom0
[/details]

Once this is done, you can restart your ‘sys-audio’ qube. If everything has been configured correctly, you should see the active qube configured to use ‘sys-audio’ in the ‘pavucontrol’ interface of ‘sys-audio’.

audiovm-pavu-3.png

Shortcuts

In your desktop environment, you can configure shortcuts. Turn up the volume: 

qvm-run sys-audio 'amixer sset Master 2%+'

Turn down the volume: 

qvm-run sys-audio 'amixer sset Master 2%-'

Toggle the audio between muted and un-muted 

qvm-run sys-audio 'amixer sset Master toggle'

Additional technical information

In ‘sys-audio’, the system needs to find all the qubes of the system (and that is configured to use ‘sys-audio’ as an audiovm) and create the communication channel to receive the audio information from those qubes. The software responsible for that can be launched manually like that: 

qvm-start-daemon --all --watch

In any qube, you can find the XID of your configured audio VM with this command: 

qubesdb-read -w /qubes-audio-domain-xid

In any qube, pulseaudio is responsible for trying to send the audio stream to the audiovm. It is done with a specific pulseaudio module ‘vchan-sink’. Depending on some specific configurations, you could create (or any other reason), you could want to manually configure this module to define the audiovm to try to use. This is done with the ‘domid’ parameter of the module. For example, in the file ‘/etc/pulse/qubes-default.pa’: 

load-module module-vchan-sink domid=XID_OF_THE_AUDIO_QUBE

In any qube, to start pulseaudio with the ‘vchan – *’ modules, run: 

start-pulseaudio-with-vchan

You can have multiple audiovm. You can configure each qubes to use a specific audiovm: 

qvm-prefs QUBE_NAME audiovm

qvm-prefs QUBE_NAME audiovm MYAUDIOVM

Special cases of non-linux HVM.

Windows qubes don't support audiovm at the moment, and are hardwired to dom0 for audio processing.

Below, example to how to add audiovm for windows qubes.

First, you need to manually edit the xen template file in dom0 "/usr/share/qubes/templates/libvirt/xen.xml"

Above the line 

{% if vm.virt_mode == 'hvm' %}

Add the following content: 

{% if vm.audiovm %}
 {% set audiovm_xid = vm.audiovm.xid %}
{% else %}
 {% set audiovm_xid = 0 %}
{% endif %}

In the rest of the file, you will find two occurences of lines starting by "cmdline=", append the following content to this line (before the closing double-quote)

 -qubes-audio:audiovm_xid={{ audiovm_xid }}

Stubdom-linux-rootfs

Then, you need to modify to patch "stubdom-linux-rootfs". In dom0, in your home directory, execute the following bash command: 

mkdir stubroot
cp /usr/libexec/xen/boot/qemu-stubdom-linux-rootfs stubroot/qemu-stubdom-linux-rootfs.gz
cd stubroot
gunzip qemu-stubdom-linux-rootfs.gz
cpio -i -d -H newc --no-absolute-filenames < qemu-stubdom-linux-rootfs
rm qemu-stubdom-linux-rootfs
nano init

After the line starting by "audio_model=", add: 

# Extract network parameters and remove them from dm_args
audio_args=$(echo "$dm_args" | sed -n '/^-qubes-audio:/p')
dm_args=$(echo "$dm_args" | sed '/^-qubes-audio:/d')

get_audio_arg() {
    echo "$audio_args" | sed -n 's/^.*[:,]'$1'=\([^,]\+\).*$/\1/p'
}

And in the rest of the file, replace 

module-vchan-sink domid=0

by 

module-vchan-sink domid=$(get_audio_arg 'audiovm_xid')

Save and close the file. Then run: 

find . -print0 | cpio --null -ov \
--format=newc | gzip -9 > ../qemu-stubdom-linux-rootfs
sudo mv ../qemu-stubdom-linux-rootfs /usr/libexec/xen/boot/

Stubdom-linux-full-rootfs

Redo the same things but for the file "stubdom-linux-full-rootfs"

Troubleshooting

USB devices

Some USB audio controller cannot be passed from a USB qube to an audio qube. In those cases, the audio qube need to also be a USB qube to have direct access to the PCI USB controller. For example, this is the case for the Sennheiser GSX 1XXX.

No sound in qubes started before audiovm

This issue is that the vchan modules of the pulseaudio daemon running in the already started qubes are not using the correct audiovm xid (ID of the xen vm). In standard setup, restarting the pulseaudio daemon is enough. Kill the pulseaudio process and run "start-pulseaudio-with-vchan". In special configuration, you may need to manually set the "domid" parameter of the vchan modules.

Audio is scratchy

It may be a power-saving issue with the sound card. In the "audio-template", create the file ‘/etc/modprobe.d/50-snd.conf’ with the following content:

options snd_hda_intel power_save=0

[details="Important note"] A lot of thoses modifications can be overwritten by update, like xen.xml, stubdom-linux-rootfs, and qvm_start_daemon. You could need to re-patch them after updates [/details]

[details="Links"] https://github.com/QubesOS/qubes-issues/issues/8093 https://github.com/QubesOS/qubes-issues/issues/8109 https://github.com/neowutran/qubes-doc/blob/sys-audio/user/advanced-topics/audio-qubes.md https://github.com/neowutran/qubes-attachment/tree/audiovm/doc [/details]