Git-Mirrors/qubes-doc
1
0
Fork 0
mirror of https://github.com/QubesOS/qubes-doc.git synced 2024-10-01 01:25:40 -04:00
Code Issues Packages Projects Releases Wiki Activity
1386e109c4
qubes-doc/basics_user/user-faq.md
Marek Marczykowski-Górecki 6d4d945243
fix formatting
2016-09-28 13:06:24 +02:00

19 KiB
Raw Blame History

layout title permalink redirect_from
doc Users' FAQ /doc/user-faq/
/en/doc/user-faq/
/doc/UserFaq/
/wiki/UserFaq/

Qubes Users' FAQ

General Questions

Installation & Hardware Compatibility

Common Problems

General Questions

Is Qubes just another Linux distribution?

If you really want to call it a distribution, then it's more of a "Xen distribution" than a Linux one. But Qubes is much more than just Xen packaging. It has its own VM management infrastructure, with support for template VMs, centralized VM updating, etc. It also has a very unique GUI virtualization infrastructure.

How is Qubes different from other security solutions?

Please see this article for a thorough discussion.

Does Qubes use full disk encryption (FDE)?

Yes, of course! Full disk encryption is enabled by default. Specifically, we use LUKS/dm-crypt. You can even manually configure your encryption parameters, if you like!

What is the main concept behind Qubes?

To build security on the “Security by Compartmentalization (or Isolation)” principle.

What about other approaches to security?

The other two popular approaches are “Security by Correctness” and “Security by Obscurity.” We don't believe either of these approaches are capable of providing reasonable security today, nor do we believe that they will be capable of doing so in the foreseeable future.

What about safe languages and formally verified microkernels?

In short: these are non-realistic solutions today. We discuss this in further depth in our Architecture Specification document.

Why does Qubes use virtualization?

We believe that this is currently the only practically viable approach to implementing strong isolation while simultaneously providing compatibility with existing applications and drivers.

What do all these terms mean?

All Qubes-specific terms are defined in the glossary.

Does Qubes run every app in a separate VM?

No! This would not make much sense. Qubes uses lightweight VMs to create security qubes (e.g., "work," "personal," and "banking,"). A typical user would likely need around five qubes. Very paranoid users, or those who are high-profile targets, might use a dozen or more qubes.

Why does Qubes use Xen instead of KVM or some other hypervisor?

In short: we believe the Xen architecture allows for the creation of more secure systems (i.e. with a much smaller TCB, which translates to a smaller attack surface). We discuss this in much greater depth in our Architecture Specification document.

What about this other/new (micro)kernel/hypervisor?

Whenever starting a discussion about another (micro)kernel or hypervisor in relation to Qubes, we strongly suggest including answers to the following questions first:

  1. What kinds of containers does it use for isolation? Processes? PV VMs? Fully virtualized VMs (HVMs)? And what underlying h/w technology is used (ring0/3, VT-x)?
  2. Does it require specially written/built applications (e.g. patched Firefox)?
  3. Does it require custom drivers, or can it use Linux/Windows ones?
  4. Does it support VT-d, and does it allow for the creation of untrusted driver domains?
  5. Does it support S3 sleep?
  6. Does it work on multiple CPUs/Chipsets?
  7. What are the performance costs, more or less? (e.g. "XYZ prevents concurrent execution of two domains/processes on shared cores of a single processor", etc.)
  8. Other special features? E.g. eliminates cooperative covert channels between VMs?

Here are the answers for Xen 4.1 (which we use as of 2014-04-28):

  1. PV and HVM Virtual Machines (ring0/3 for PV domains, VT-x/AMD-v for HVMs).
  2. Runs unmodified usermode apps (binaries).
  3. Runs unmodified Linux drivers (dom0 and driver domains). PV VMs require special written pvdrivers.
  4. Full VT-d support including untrusted driver domains.
  5. S3 sleep supported well.
  6. Works on most modern CPUs/Chipsets.
  7. Biggest performance hit on disk operations (especially in Qubes when complex 2-layer mapping used for Linux qubes). No GPU virtualization.
  8. Mostly WorksTM :)

What's so special about Qubes' GUI virtualization?

We have designed the GUI virtualization subsystem with two primary goals: security and performance. Our GUI infrastructure introduces only about 2,500 lines of C code (LOC) into the privileged domain (Dom0), which is very little, and thus leaves little space for bugs and potential attacks. At the same time, due to the smart use of Xen shared memory, our GUI implementation is very efficient, so most virtualized applications really feel as if they were executed natively.

Can I watch YouTube videos in qubes?

Absolutely.

Can I run applications, like games, which require 3D support?

Those won’t fly. We do not provide OpenGL virtualization for qubes. This is mostly a security decision, as implementing such a feature would most likely introduce a great deal of complexity into the GUI virtualization infrastructure. However, Qubes does allow for the use of accelerated graphics (OpenGL) in Dom0’s Window Manager, so all the fancy desktop effects should still work.

For further discussion about the potential for GPU passthorugh on Xen/Qubes, please see the following threads:

Is Qubes a multi-user system?

No. Qubes does not pretend to be a multi-user system. Qubes assumes that the user who controls Dom0 controls the whole system. It would be very difficult to securely implement multi-user support. See here for details.

Why passwordless sudo?

Please refer to this page.

How should I report documentation issues?

Please see the documentation guidelines.

Will Qubes seek to get certified under the GNU Free System Distribution Guidelines (GNU FSDG)?

Not currently, for the same reasons that Debian is not certified.

Installation & Hardware Compatibility

(See also: System Requirements, Hardware Compatibility List, and Certified Laptops.)

How much disk space does each qube require?

Each qube is created from a TemplateVM and shares the root filesystem with this TemplateVM (in a read-only manner). This means that each qube needs only as much disk space as is necessary to store its own private data. This also means that it is possible to update the software for several qubes simultaneously by running a single update process in the TemplateVM upon which those qubes are based. (These qubes will then have to be restarted in order for the update to take effect in them.)

How much memory is recommended for Qubes?

At least 4 GB. It is possible to install Qubes on a system with 2 GB of RAM, but the system would probably not be able to run more than three qubes at a time.

Can I install Qubes on a system without VT-x?

Yes. Xen doesn't use VT-x (or AMD-v) for PV guest virtualization. (It uses ring0/3 separation instead.) However, without VT-x, you won't be able to use fully virtualized VMs (e.g., Windows-based qubes), which were introduced in Qubes 2. In addition, if your system lacks VT-x, then it also lacks VT-d. (See next question.)

Can I install Qubes on a system without VT-d?

Yes. You can even run a NetVM, but you will not benefit from DMA protection for driver domains. On a system without VT-d, everything should work in the same way, except there will be no real security benefit to having a separate NetVM, as an attacker could always use a simple DMA attack to go from the NetVM to Dom0. Nonetheless, all of Qubes' other security mechanisms, such as qube separation, work without VT-d. Therefore, a system running Qubes will still be significantly more secure than one running Windows, Mac, or Linux, even if it lacks VT-d.

What is a DMA attack?

DMA is mechanism for PCI devices to access system memory (read/write). Without VT-d, any PCI device can access all the memory, regardless to which VM it is assigned (or if it is left in dom0). Most PCI devices allow the driver to request an arbitrary DMA operation (like "put received network packets at this address in memory", or "get this memory area and send it to the network"). So, without VT-d, it gives unlimited access to the whole system. Now, it is only a matter of knowing where to read/write to take over the system, instead of just crashing. But since you can read the whole memory, it isn't that hard.

Now, how does this apply to Qubes OS? The above attack requires access to a PCI device, which means that it can be performed only from NetVM / UsbVM, so someone must first break into one of those VMs. But this isn't that hard, because there is a lot of complex code handling network traffic. Recent bugs includes DHCP client, DNS client, etc. Most attacks on NetVM / UsbVM (but not all!) require being somewhat close to the target system - for example connected to the same WiFi network, or in the case of a UsbVM, having physical acccess to a USB port.

Can I use AMD-v instead of VT-x?

See this message.

Can I install Qubes in a virtual machine (e.g., on VMWare)?

Some users have been able to do this, but it is neither recommended nor supported. Qubes should be installed bare-metal. (After all, it uses its own bare-metal hypervisor!)

Why does my network adapter not work?

You may have an adapter (wired, wireless), that is not compatible with open-source drivers shipped by Qubes. There may be a binary blob, which provides drivers in the linux-firmware package.

Open a terminal and run sudo yum install linux-firmware in the TemplateVM upon which your NetVM is based. You have to restart the NetVM after the TemplateVM has been shut down.

Can I install Qubes OS together with other operating system (dual-boot/multi-boot)?

You shouldn't do that, because it pose a security risk for your Qubes OS installation. But if you understand the risk and accept it, read documentation on multibooting. It starts with explanation what is wrong with using such setup.

Common Problems

My qubes lost Internet access after a TemplateVM update. What should I do?

Run systemctl enable NetworkManager-dispatcher.service in the TemplateVM upon which your NetVM is based. You may have to reboot afterward for the change to take effect. (Note: This is an upstream problem. See here. For details, see the qubes-users mailing list threads here and here.)

My keyboard layout settings are not behaving correctly. What should I do?

Please read this discussion.

My dom0 and/or TemplateVM update stalls when attempting to update via the GUI tool. What should I do?

This can usually be fixed by updating via the command line.

In dom0, open a terminal and run sudo qubes-dom0-update.

In your TemplateVMs, open a terminal and run sudo yum upgrade.

How do I run a Windows HVM in non-seamless mode (i.e., as a single window)?

Enable "debug mode" in the qube's settings, either by checking the box labeled "Run in debug mode" in the Qubes VM Manager qube settings menu or by running the qvm-prefs command.)

I created a usbVM and assigned usb controllers to it. Now the usbVM wont boot.

This is probably because one of the controllers does not support reset. In Qubes R2 any such errors were ignored but in Qubes R3.0 they are not. A device that does not support reset is not safe and generally should not be assigned to a VM.

Most likely the offending controller is a USB3.0 device. You can remove this controller from the usbVM, and see if this allows the VM to boot. Alternatively you may be able to disable USB 3.0 in the BIOS.

Errors suggesting this issue:

  • in xl dmesg output:

     (XEN) [VT-D] It's disallowed to assign 0000:00:1a.0 with shared RMRR at dbe9a000 for Dom19.
 (XEN) XEN_DOMCTL_assign_device: assign 0000:00:1a.0 to dom19 failed (-1)

  • during qvm-start sys-usb:

     internal error: Unable to reset PCI device [...]  no FLR, PM reset or bus reset available.

Another solution would be to set the pci_strictreset option using qvm-prefs in dom0:

qvm-prefs usbVM -s pci_strictreset false

This option allows the VM to ignore the error and the VM will start. Please review the note on this page and be aware of the potential risk.

I assigned a PCI device to a qube, then unassigned it/shut down the qube. Why isn't the device available in dom0?

This is an intended feature. A device which was previously assigned to a less trusted qube could attack dom0 if it were automatically reassigned there. In order to re-enable the device in dom0, either:

  • Reboot the physical machine.

or

  • Go to the sysfs (/sys/bus/pci), find the right device, detach it from the pciback driver and attach back to the original driver. Replace <BDF> with your device, for example 00:1c.2:

     echo 0000:<BDF> > /sys/bus/pci/drivers/pciback/unbind
 MODALIAS=`cat /sys/bus/pci/devices/0000:<BDF>/modalias`
 MOD=`modprobe -R $MODALIAS | head -n 1`
 echo 0000:<BDF> > /sys/bus/pci/drivers/$MOD/bind

How do I install Flash in a Debian qube?

The Debian way is to install the flashplugin-nonfree package. Do this in a Debian template. You will have to allow Full access in the firewall prior to installation. This will make Flash available to every qube using that template.

If you only want Flash available in one qube:

  • download the Flash Player for linux (64 bit) .tar.gz from Adobe.
  • untar the downloaded file tar xf install_flash_player_11_linux.x86_64.tar.gz
  • create ~/.mozilla/plugins if it does not exist
  • move libflashhplayer.so to ~/.mozilla/plugins, and restart iceweasel.