mirror of
https://github.com/QubesOS/qubes-doc.git
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Merge branch 'Yethal-patch-6'
This commit is contained in:
Andrew David Wong
commit
b09d12764f
@ -17,6 +17,174 @@ redirect_from:
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Using and Managing USB Devices
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==============================
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Creating and Using a USB qube
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-----------------------------
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The connection of an untrusted USB device to dom0 is a security risk since dom0,
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like almost every OS, reads partition tables automatically and since the whole
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USB stack is put to work to parse the data presented by the USB device in order
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to determine if it is a USB mass storage device, to read its configuration, etc.
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This happens even if the drive is then assigned and mounted in another qube.
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To avoid this risk, it is possible to prepare and utilize a USB qube.
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A USB qube acts as a secure handler for potentially malicious USB devices,
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preventing them from coming into contact with dom0 (which could otherwise be
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fatal to the security of the whole system). With a USB qube, every time you
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connect an untrusted USB drive to a USB port managed by that USB controller, you
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will have to attach it to the qube in which you wish to use it (if different
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from the USB qube itself), either by using Qubes VM Manager or the command line
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(see instructions above).
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You can create a USB qube using the management stack by performing the following
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steps as root in dom0:
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1. Enable `sys-usb`:
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qubesctl top.enable qvm.sys-usb
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2. Apply the configuration:
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qubesctl state.highstate
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Alternatively, you can create a USB qube manually as follows:
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1. Read the [Assigning Devices] page to learn how to list and identify your
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USB controllers. Carefully check whether you have a USB controller that
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would be appropriate to assign to a USB qube. Note that it should be free
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of input devices, programmable devices, and any other devices that must be
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directly available to dom0. If you find a free controller, note its name
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and proceed to step 2.
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2. Create a new qube. Give it an appropriate name and color label
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(recommended: `sys-usb`, red). If you need to attach a networking device,
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it might make sense to create a NetVM. If not, an AppVM might make more
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sense. (The default `sys-usb` is a NetVM.)
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3. In the qube's settings, go to the "Devices" tab. Find the USB controller
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that you identified in step 1 in the "Available" list. Move it to the
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"Selected" list.
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**Caution:** By assigning a USB controller to a USB qube, it will no longer
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be available to dom0. This can make your system unusable if, for example,
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you have only one USB controller, and you are running Qubes off of a USB
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drive.
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4. Click "OK." Restart the qube.
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5. Recommended: Check the box on the "Basic" tab which says "Start VM
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automatically on boot." (This will help to mitigate attacks in which
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someone forces your system to reboot, then plugs in a malicious USB
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device.)
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If the USB qube will not start, see [here][faq-usbvm].
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How to hide all USB controllers from dom0
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-----------------------------------------
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If you create a USB qube manually, there will be a brief period of time during the
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boot process during which dom0 will be exposed to your USB controllers (and any
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attached devices). This is a potential security risk, since even brief exposure
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to a malicious USB device could result in dom0 being compromised. There are two
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approaches to this problem:
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1. Physically disconnect all USB devices whenever you reboot the host.
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2. Hide (i.e., blacklist) all USB controllers from dom0.
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**Warning:** If you use a USB [AEM] device, do not use the second option. Using
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a USB AEM device requires dom0 to have access to the USB controller to which
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your USB AEM device is attached. If dom0 cannot read your USB AEM device, AEM
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will hang.
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The procedure to hide all USB controllers from dom0 is as follows:
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1. Open the file `/etc/default/grub` in dom0.
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2. Find the line that begins with `GRUB_CMDLINE_LINUX`.
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3. Add `rd.qubes.hide_all_usb` to that line.
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4. Save and close the file.
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5. Run the command `grub2-mkconfig -o /boot/grub2/grub.cfg` in dom0.
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6. Reboot.
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(Note: Beginning with R3.2, `rd.qubes.hide_all_usb` is set automatically if you
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opt to create a USB qube during installation. This also occurs automatically if
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you choose to [create a USB qube] using the `qubesctl` method, which is the
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first pair of steps in the linked section.)
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**Warning** USB keyboard cannot be used to type the disk passphrase
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if USB controllers were hidden from dom0. Before hiding USB controllers
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make sure your laptop keyboard is not internally connected via USB
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(by checking output of `lsusb` command) or that you have a PS/2 keyboard at hand
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(if using a desktop PC). Failure to do so will render your system unusable.
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Removing a USB qube
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-------------------
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**Warning:** This procedure will result in your USB controller(s) being attached
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directly to dom0.
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1. Shut down the USB qube.
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2. In Qubes Manager, right-click on the USB qube and select "Remove VM."
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3. Open the file `/etc/default/grub` in dom0.
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4. Find the line(s) that begins with `GRUB_CMDLINE_LINUX`.
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5. If `rd.qubes.hide_all_usb` appears anywhere in those lines, remove it.
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6. Save and close the file.
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7. Run the command `grub2-mkconfig -o /boot/grub2/grub.cfg` in dom0.
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8. Reboot.
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Security Warning about USB Input Devices
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----------------------------------------
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**Important security warning. Please read this section carefully!**
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If you connect USB input devices (keyboard and mouse) to a VM, that VM will effectively have control over your system.
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Because of this, the benefits of using a USB qube are much smaller than using a fully untrusted USB qube.
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In addition to having control over your system, such VM can also sniff all the input your enter there (for example, passwords in the case of a USB keyboard).
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There is no simple way to protect against sniffing, but you can make it harder to exploit control over input devices.
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If you have only a USB mouse connected to a USB qube, but the keyboard is connected directly to dom0 (using a PS/2 connector, for example), you simply need to lock the screen when you are away from your computer.
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You must do this every time you leave your computer unattended, even if there no risk of anyone else having direct physical access to your computer.
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This is because you are guarding the system not only against anyone with local access, but also against possible actions from a potentially compromised USB qube.
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If your keyboard is also connected to a USB qube, things are much harder.
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Locking the screen (with a traditional password) does not solve the problem, because the USB qube can simply sniff this password and later easily unlock the screen.
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One possibility is to set up the screen locker to require an additional step to unlock (i.e., two-factor authentication).
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One way to achieve this is to use a [YubiKey], or some other hardware token, or even to manually enter a one-time password.
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How to use a USB keyboard
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-------------------------
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**Caution:** Please carefully read the [Security Warning about USB Input Devices] before proceeding.
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In order to use a USB keyboard, you must first attach it to a USB qube, then give that qube permission to pass keyboard input to dom0.
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Edit the `qubes.InputKeyboard` policy file in dom0, which is located here:
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/etc/qubes-rpc/policy/qubes.InputKeyboard
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Add a line like this one to the top of the file:
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sys-usb dom0 ask,user=root
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(Change `sys-usb` to your desired USB qube.)
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You can now use your USB keyboard.
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How to use a USB mouse
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----------------------
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**Caution:** Please carefully read the [Security Warning about USB Input Devices] before proceeding.
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In order to use a USB mouse, you must first attach it to a USB qube, then give that qube permission to pass mouse input to dom0.
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Edit the `qubes.InputMouse` policy file in dom0, which is located here:
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/etc/qubes-rpc/policy/qubes.InputMouse
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Add a line like this to the op of the file:
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sys-usb dom0 ask,user=root
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(Change `sys-usb` to your desired USB qube.)
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You can now use your USB mouse.
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How to attach USB drives
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------------------------
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@ -102,11 +270,7 @@ follows:
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Otherwise, you will not be able to attach it anywhere later. See issue [1082]
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for details.
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There have been reports that when attaching a single partition, the Nautilus
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file manager would not see it and automatically mount it (see issue [623]).
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This problem seems to be resolved (see [this comment on issue 1072][1072-comm1]).
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If, however, the device does not appear in Nautilus, you will need to mount it
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If the device does not appear in Nautilus, you will need to mount it
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manually. The device will show up as `/dev/xvdi` (or `/dev/xvdj` if there is
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already one device attached -- if two, `/dev/xvdk`, and so on).
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@ -147,162 +311,6 @@ steps:
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`qvm-block -d` command.
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Creating and Using a USB qube
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-----------------------------
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The connection of an untrusted USB device to dom0 is a security risk since dom0,
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like almost every OS, reads partition tables automatically and since the whole
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USB stack is put to work to parse the data presented by the USB device in order
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to determine if it is a USB mass storage device, to read its configuration, etc.
|
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This happens even if the drive is then assigned and mounted in another qube.
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|
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To avoid this risk, it is possible to prepare and utilize a USB qube.
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For this reason, you may wish to avoid using a USB qube if you do not have a USB
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controller free of input devices and programmable devices, although Qubes R3.1
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introduced support for USB mice and keyboards (see below).
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A USB qube acts as a secure handler for potentially malicious USB devices,
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preventing them from coming into contact with dom0 (which could otherwise be
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fatal to the security of the whole system). With a USB qube, every time you
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connect an untrusted USB drive to a USB port managed by that USB controller, you
|
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will have to attach it to the qube in which you wish to use it (if different
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from the USB qube itself), either by using Qubes VM Manager or the command line
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(see instructions above). Again, this works only for USB mass storage devices.
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Other devices cannot currently be virtualized.
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You can create a USB qube using the management stack by performing the following
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steps as root in dom0:
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1. Enable `sys-usb`:
|
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qubesctl top.enable qvm.sys-usb
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||||
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2. Apply the configuration:
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||||
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qubesctl state.highstate
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||||
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||||
(Note: This automatically [hides all USB controllers from dom0][hide-usb].)
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Alternatively, you can create a USB qube manually as follows:
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||||
|
||||
1. Read the [Assigning Devices] page to learn how to list and identify your
|
||||
USB controllers. Carefully check whether you have a USB controller that
|
||||
would be appropriate to assign to a USB qube. Note that it should be free
|
||||
of input devices, programmable devices, and any other devices that must be
|
||||
directly available to dom0. If you find a free controller, note its name
|
||||
and proceed to step 2.
|
||||
2. Create a new qube. Give it an appropriate name and color label
|
||||
(recommended: `sys-usb`, red). If you need to attach a networking device,
|
||||
it might make sense to create a NetVM. If not, an AppVM might make more
|
||||
sense. (The default `sys-usb` is a NetVM.)
|
||||
3. In the qube's settings, go to the "Devices" tab. Find the USB controller
|
||||
that you identified in step 1 in the "Available" list. Move it to the
|
||||
"Selected" list.
|
||||
|
||||
**Caution:** By assigning a USB controller to a USB qube, it will no longer
|
||||
be available to dom0. This can make your system unusable if, for example,
|
||||
you have only one USB controller, and you are running Qubes off of a USB
|
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drive.
|
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|
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4. Click "OK." Restart the qube.
|
||||
5. Recommended: Check the box on the "Basic" tab which says "Start VM
|
||||
automatically on boot." (This will help to mitigate attacks in which
|
||||
someone forces your system to reboot, then plugs in a malicious USB
|
||||
device.)
|
||||
|
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If the USB qube will not start, see [here][faq-usbvm].
|
||||
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Removing a USB qube
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-------------------
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**Warning:** This procedure will result in your USB controller(s) being attached
|
||||
directly to dom0.
|
||||
|
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1. Shut down the USB qube.
|
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2. In Qubes Manager, right-click on the USB qube and select "Remove VM."
|
||||
3. Open the file `/etc/default/grub` in dom0.
|
||||
4. Find the line(s) that begins with `GRUB_CMDLINE_LINUX`.
|
||||
5. If `rd.qubes.hide_all_usb` appears anywhere in those lines, remove it.
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||||
6. Save and close the file.
|
||||
7. Run the command `grub2-mkconfig -o /boot/grub2/grub.cfg` in dom0.
|
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8. Reboot.
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|
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How to hide all USB controllers from dom0
|
||||
-----------------------------------------
|
||||
|
||||
Even if you create a USB qube, there will be a brief period of time during the
|
||||
boot process during which dom0 will be exposed to your USB controllers (and any
|
||||
attached devices). This is a potential security risk, since even brief exposure
|
||||
to a malicious USB device could result in dom0 being compromised. There are two
|
||||
approaches to this problem:
|
||||
|
||||
1. Physically disconnect all USB devices whenever you reboot the host.
|
||||
2. Hide (i.e., blacklist) all USB controllers from dom0.
|
||||
|
||||
**Warning:** If you use a USB [AEM] device, do not use the second option. Using
|
||||
a USB AEM device requires dom0 to have access to the USB controller to which
|
||||
your USB AEM device is attached. If dom0 cannot read your USB AEM device, AEM
|
||||
will hang.
|
||||
|
||||
The procedure to hide all USB controllers from dom0 is as follows:
|
||||
|
||||
1. Open the file `/etc/default/grub` in dom0.
|
||||
2. Find the line that begins with `GRUB_CMDLINE_LINUX`.
|
||||
3. Add `rd.qubes.hide_all_usb` to that line.
|
||||
4. Save and close the file.
|
||||
5. Run the command `grub2-mkconfig -o /boot/grub2/grub.cfg` in dom0.
|
||||
6. Reboot.
|
||||
|
||||
(Note: Beginning with R3.2, `rd.qubes.hide_all_usb` is set automatically if you
|
||||
opt to create a USB qube during installation. This also occurs automatically if
|
||||
you choose to [create a USB qube] using the `qubesctl` method, which is the
|
||||
first pair of steps in the linked section.)
|
||||
|
||||
Supported USB device types
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--------------------------
|
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As of Qubes R3.1, it is possible to attach:
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* USB mice
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* USB keyboards (see below)
|
||||
* USB block devices (such as USB mass storage devices)
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* When attaching one of these, you should get a notification about the
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new device, then you should be able to attach it to a qube in Qubes VM
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||||
Manager.
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Other devices, such as USB webcams, will also work, but they will be
|
||||
accessible only from the USB qube itself, as explained above.
|
||||
|
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|
||||
How to use a USB keyboard
|
||||
-------------------------
|
||||
|
||||
In order to use a USB keyboard, you must first attach it to a USB qube, then
|
||||
give that qube permission to pass keyboard input to dom0. Note that allowing
|
||||
keyboard access from a USB qube gives it great power. In short:
|
||||
|
||||
* It will see whatever you type on that keyboard (including passwords).
|
||||
* It will be able to inject keystrokes, which basically means that it will be
|
||||
able to enter any command. For example, if some malware catches your
|
||||
screenlocker password, it will be able to unlock the screen when you are not
|
||||
present. (For more details, see [here][input-proxy].)
|
||||
|
||||
If you are sure you wish to proceed, then you must edit the
|
||||
`qubes.InputKeyboard` policy file in dom0, which is located here:
|
||||
|
||||
/etc/qubes-rpc/policy/qubes.InputKeyboard
|
||||
|
||||
Add a line like this one to the top of the file:
|
||||
|
||||
sys-usb dom0 ask,user=root
|
||||
|
||||
(Change `sys-usb` to your desired USB qube.)
|
||||
|
||||
You can now use your USB keyboard.
|
||||
|
||||
Attaching a single USB device to a qube (USB passthrough)
|
||||
---------------------------------------------------------
|
||||
|
||||
@ -358,7 +366,8 @@ This feature is not yet available in Qubes Manager however, if you would like to
|
||||
[AEM]: /doc/anti-evil-maid/
|
||||
[1618]: https://github.com/QubesOS/qubes-issues/issues/1618
|
||||
[create a USB qube]: #creating-and-using-a-usb-qube
|
||||
[input-proxy]: https://github.com/qubesos/qubes-app-linux-input-proxy
|
||||
[usb-challenges]: http://blog.invisiblethings.org/2011/05/31/usb-security-challenges.html
|
||||
[project-page]: https://www.qubes-os.org/gsoc/
|
||||
[project-page]: /gsoc/
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||||
[gsoc-page]: https://summerofcode.withgoogle.com/organizations/6239659689508864/
|
||||
[YubiKey]: /doc/YubiKey/
|
||||
[Security Warning about USB Input Devices]: #security-warning-about-usb-input-devices
|
||||
|
||||
Loading…
Reference in New Issue
Block a user