2013-05-03 14:25:37 +00:00
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<?xml version="1.0" encoding="UTF-8"?>
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2017-07-26 17:01:25 +00:00
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<!DOCTYPE html>
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2013-05-03 14:25:37 +00:00
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<html xmlns="http://www.w3.org/1999/xhtml">
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2008-04-23 17:08:31 +00:00
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<body>
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2011-07-15 18:33:17 +00:00
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<h1>KVM/QEMU hypervisor driver</h1>
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2008-04-23 17:08:31 +00:00
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2009-05-21 14:20:21 +00:00
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<ul id="toc"></ul>
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2008-04-23 17:08:31 +00:00
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<p>
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2011-07-15 18:33:17 +00:00
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The libvirt KVM/QEMU driver can manage any QEMU emulator from
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2018-10-23 09:21:04 +00:00
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version 1.5.0 or later.
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2008-04-23 17:08:31 +00:00
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</p>
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2017-07-26 14:52:42 +00:00
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<h2><a id="project">Project Links</a></h2>
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2011-07-15 18:33:17 +00:00
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<ul>
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<li>
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2017-10-13 15:30:41 +00:00
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The <a href="https://www.linux-kvm.org/">KVM</a> Linux
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2011-07-15 18:33:17 +00:00
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hypervisor
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2013-05-03 14:25:37 +00:00
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</li>
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2011-07-15 18:33:17 +00:00
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<li>
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2017-10-13 15:30:41 +00:00
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The <a href="https://wiki.qemu.org/Index.html">QEMU</a> emulator
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2011-07-15 18:33:17 +00:00
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</li>
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</ul>
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2017-07-26 14:52:42 +00:00
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<h2><a id="prereq">Deployment pre-requisites</a></h2>
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2008-04-23 17:08:31 +00:00
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<ul>
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<li>
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2009-11-06 15:04:19 +00:00
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<strong>QEMU emulators</strong>: The driver will probe <code>/usr/bin</code>
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for the presence of <code>qemu</code>, <code>qemu-system-x86_64</code>,
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2011-07-07 02:45:05 +00:00
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<code>qemu-system-microblaze</code>,
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<code>qemu-system-microblazeel</code>,
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2009-11-06 15:04:19 +00:00
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<code>qemu-system-mips</code>,<code>qemu-system-mipsel</code>,
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<code>qemu-system-sparc</code>,<code>qemu-system-ppc</code>. The results
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of this can be seen from the capabilities XML output.
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2008-04-23 17:08:31 +00:00
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</li>
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<li>
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2009-11-06 15:04:19 +00:00
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<strong>KVM hypervisor</strong>: The driver will probe <code>/usr/bin</code>
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for the presence of <code>qemu-kvm</code> and <code>/dev/kvm</code> device
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2019-07-17 11:46:37 +00:00
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node. If both are found, then KVM fully virtualized, hardware accelerated
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2009-11-06 15:04:19 +00:00
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guests will be available.
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2008-04-23 17:08:31 +00:00
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</li>
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</ul>
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2017-07-26 14:52:42 +00:00
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<h2><a id="uris">Connections to QEMU driver</a></h2>
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2009-01-27 14:49:09 +00:00
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<p>
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The libvirt QEMU driver is a multi-instance driver, providing a single
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system wide privileged driver (the "system" instance), and per-user
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2009-11-30 15:21:21 +00:00
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unprivileged drivers (the "session" instance). The URI driver protocol
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2012-08-22 18:29:18 +00:00
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is "qemu". Some example connection URIs for the libvirt driver are:
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2009-01-27 14:49:09 +00:00
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</p>
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2009-11-13 23:09:20 +00:00
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<pre>
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qemu:///session (local access to per-user instance)
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qemu+unix:///session (local access to per-user instance)
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qemu:///system (local access to system instance)
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qemu+unix:///system (local access to system instance)
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qemu://example.com/system (remote access, TLS/x509)
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qemu+tcp://example.com/system (remote access, SASl/Kerberos)
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qemu+ssh://root@example.com/system (remote access, SSH tunnelled)
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</pre>
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2009-01-27 14:49:09 +00:00
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2019-05-17 11:35:57 +00:00
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<h3><a id="uriembedded">Embedded driver</a></h3>
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<p>
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2020-01-27 15:38:19 +00:00
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Since 6.1.0 the QEMU driver has experimental support for operating
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2019-05-17 11:35:57 +00:00
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in an embedded mode. In this scenario, rather than connecting to
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the libvirtd daemon, the QEMU driver runs in the client application
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process directly. To use this the client application must have
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registered & be running an instance of the event loop. To open
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the driver in embedded mode the app use the new URI path and specify
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a virtual root directory under which the driver will create content.
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</p>
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<pre>
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qemu:///embed?root=/some/dir
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</pre>
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<p>
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Broadly speaking the range of functionality is intended to be
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on a par with that seen when using the traditional system or
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session libvirt connections to QEMU. The features will of course
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differ depending on whether the application using the embedded
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driver is running privileged or unprivileged. For example PCI
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device assignment or TAP based networking are only available
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when running privileged. While the embedded mode is still classed
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as experimental some features may change their default settings
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between releases.
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</p>
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<p>
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By default if the application uses any APIs associated with
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secondary drivers, these will result in a connection being
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opened to the corresponding driver in libvirtd. For example,
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this allows a virtual machine from the embedded QEMU to connect
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its NIC to a virtual network or connect its disk to a storage
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volume. Some of the secondary drivers will also be able to support
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running in embedded mode. Currently this is supported by the
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secrets driver, to allow for use of VMs with encrypted disks
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</p>
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<h4><a id="embedTree">Directory tree</a></h4>
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<p>
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Under the specified root directory the following locations will
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be used
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</p>
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<pre>
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/some/dir
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+- log
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| +- qemu
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| +- swtpm
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+- etc
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| +- qemu
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| +- pki
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| +- qemu
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+- run
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| +- qemu
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| +- swtpm
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+- cache
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| +- qemu
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+- lib
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+- qemu
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+- swtpm
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</pre>
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<p>
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Note that UNIX domain sockets used for QEMU virtual machines had
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a maximum filename length of 108 characters. Bear this in mind
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when picking a root directory to avoid risk of exhausting the
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filename space. The application is responsible for recursively
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purging the contents of this directory tree once they no longer
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require a connection, though it can also be left intact for reuse
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when opening a future connection.
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</p>
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2020-01-27 15:38:19 +00:00
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<h4><a id="embedAPI">API usage with event loop</a></h4>
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2019-05-17 11:35:57 +00:00
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<p>
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To use the QEMU driver in embedded mode the application must
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register an event loop with libvirt. Many of the QEMU driver
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API calls will rely on the event loop processing data. With this
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in mind, applications must <strong>NEVER</strong> invoke API
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calls from the event loop thread itself, only other threads.
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Not following this rule will lead to deadlocks in the API.
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This restriction is intended to be lifted in a future release
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of libvirt, once QMP processing moves to a dedicated thread.
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</p>
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2017-07-26 14:52:42 +00:00
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<h2><a id="security">Driver security architecture</a></h2>
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2009-08-19 13:17:17 +00:00
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<p>
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There are multiple layers to security in the QEMU driver, allowing for
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flexibility in the use of QEMU based virtual machines.
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</p>
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2017-07-26 14:52:42 +00:00
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<h3><a id="securitydriver">Driver instances</a></h3>
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2009-08-19 13:17:17 +00:00
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<p>
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As explained above there are two ways to access the QEMU driver
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in libvirt. The "qemu:///session" family of URIs connect to a
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libvirtd instance running as the same user/group ID as the client
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application. Thus the QEMU instances spawned from this driver will
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share the same privileges as the client application. The intended
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use case for this driver is desktop virtualization, with virtual
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2010-11-01 20:57:18 +00:00
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machines storing their disk images in the user's home directory and
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2009-08-19 13:17:17 +00:00
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being managed from the local desktop login session.
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</p>
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<p>
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The "qemu:///system" family of URIs connect to a
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libvirtd instance running as the privileged system account 'root'.
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Thus the QEMU instances spawned from this driver may have much
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higher privileges than the client application managing them.
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The intended use case for this driver is server virtualization,
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where the virtual machines may need to be connected to host
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resources (block, PCI, USB, network devices) whose access requires
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elevated privileges.
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</p>
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2017-07-26 14:52:42 +00:00
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<h3><a id="securitydac">POSIX users/groups</a></h3>
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2009-08-19 13:17:17 +00:00
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<p>
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2009-08-19 16:02:45 +00:00
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In the "session" instance, the POSIX users/groups model restricts QEMU
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virtual machines (and libvirtd in general) to only have access to resources
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2009-08-19 13:17:17 +00:00
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with the same user/group ID as the client application. There is no
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finer level of configuration possible for the "session" instances.
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</p>
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<p>
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In the "system" instance, libvirt releases from 0.7.0 onwards allow
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control over the user/group that the QEMU virtual machines are run
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as. A build of libvirt with no configuration parameters set will
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still run QEMU processes as root:root. It is possible to change
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this default by using the --with-qemu-user=$USERNAME and
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--with-qemu-group=$GROUPNAME arguments to 'configure' during
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build. It is strongly recommended that vendors build with both
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of these arguments set to 'qemu'. Regardless of this build time
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default, administrators can set a per-host default setting in
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the <code>/etc/libvirt/qemu.conf</code> configuration file via
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the <code>user=$USERNAME</code> and <code>group=$GROUPNAME</code>
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parameters. When a non-root user or group is configured, the
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libvirt QEMU driver will change uid/gid to match immediately
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before executing the QEMU binary for a virtual machine.
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</p>
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<p>
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If QEMU virtual machines from the "system" instance are being
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run as non-root, there will be greater restrictions on what
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host resources the QEMU process will be able to access. The
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libvirtd daemon will attempt to manage permissions on resources
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2009-08-19 16:02:45 +00:00
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to minimise the likelihood of unintentional security denials,
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2009-08-19 13:17:17 +00:00
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but the administrator / application developer must be aware of
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some of the consequences / restrictions.
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</p>
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<ul>
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<li>
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<p>
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The directories <code>/var/run/libvirt/qemu/</code>,
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<code>/var/lib/libvirt/qemu/</code> and
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<code>/var/cache/libvirt/qemu/</code> must all have their
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ownership set to match the user / group ID that QEMU
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guests will be run as. If the vendor has set a non-root
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user/group for the QEMU driver at build time, the
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permissions should be set automatically at install time.
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If a host administrator customizes user/group in
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<code>/etc/libvirt/qemu.conf</code>, they will need to
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manually set the ownership on these directories.
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</p>
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</li>
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<li>
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<p>
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2009-08-19 16:02:45 +00:00
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When attaching USB and PCI devices to a QEMU guest,
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2009-08-19 13:17:17 +00:00
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QEMU will need to access files in <code>/dev/bus/usb</code>
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2009-08-19 16:02:45 +00:00
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and <code>/sys/bus/pci/devices</code> respectively. The libvirtd daemon
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2009-08-19 13:17:17 +00:00
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will automatically set the ownership on specific devices
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that are assigned to a guest at start time. There should
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not be any need for administrator changes in this respect.
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</p>
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</li>
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<li>
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<p>
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Any files/devices used as guest disk images must be
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accessible to the user/group ID that QEMU guests are
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configured to run as. The libvirtd daemon will automatically
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set the ownership of the file/device path to the correct
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user/group ID. Applications / administrators must be aware
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though that the parent directory permissions may still
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deny access. The directories containing disk images
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must either have their ownership set to match the user/group
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configured for QEMU, or their UNIX file permissions must
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have the 'execute/search' bit enabled for 'others'.
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</p>
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<p>
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The simplest option is the latter one, of just enabling
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the 'execute/search' bit. For any directory to be used
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2009-08-19 16:02:45 +00:00
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for storing disk images, this can be achieved by running
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2009-08-19 13:17:17 +00:00
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the following command on the directory itself, and any
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parent directories
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</p>
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<pre>
|
2009-11-13 23:09:20 +00:00
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chmod o+x /path/to/directory
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2009-08-19 13:17:17 +00:00
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</pre>
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<p>
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In particular note that if using the "system" instance
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and attempting to store disk images in a user home
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directory, the default permissions on $HOME are typically
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too restrictive to allow access.
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</p>
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</li>
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</ul>
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<p>
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2019-11-28 14:27:54 +00:00
|
|
|
The libvirt maintainers <strong>strongly recommend against</strong>
|
|
|
|
|
running QEMU as the root user/group. This should not be required
|
|
|
|
|
in most supported usage scenarios, as libvirt will generally do the
|
|
|
|
|
right thing to grant QEMU access to files it is permitted to
|
|
|
|
|
use when it is running non-root.
|
2009-08-19 13:17:17 +00:00
|
|
|
</p>
|
|
|
|
|
|
2019-11-28 14:27:54 +00:00
|
|
|
<h3><a id="securitycap">Linux process capabilities</a></h3>
|
|
|
|
|
|
2009-08-19 13:17:17 +00:00
|
|
|
<p>
|
2019-11-28 14:27:54 +00:00
|
|
|
In versions of libvirt prior to 6.0.0, even if QEMU was configured
|
|
|
|
|
to run as the root user / group, libvirt would strip all process
|
|
|
|
|
capabilities. This meant that QEMU could only read/write files
|
|
|
|
|
owned by root, or with open permissions. In reality, stripping
|
|
|
|
|
capabilities did not have any security benefit, as it was trivial
|
|
|
|
|
to get commands to run in another context with full capabilities,
|
|
|
|
|
for example, by creating a cronjob.
|
2009-08-19 13:17:17 +00:00
|
|
|
</p>
|
|
|
|
|
<p>
|
2019-11-28 14:27:54 +00:00
|
|
|
Thus since 6.0.0, if QEMU is running as root, it will keep all
|
|
|
|
|
process capabilities. Behaviour when QEMU is running non-root
|
|
|
|
|
is unchanged, it still has no capabilities.
|
2009-08-19 13:17:17 +00:00
|
|
|
</p>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h3><a id="securityselinux">SELinux basic confinement</a></h3>
|
2009-08-19 13:17:17 +00:00
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The basic SELinux protection for QEMU virtual machines is intended to
|
|
|
|
|
protect the host OS from a compromised virtual machine process. There
|
|
|
|
|
is no protection between guests.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
In the basic model, all QEMU virtual machines run under the confined
|
|
|
|
|
domain <code>root:system_r:qemu_t</code>. It is required that any
|
|
|
|
|
disk image assigned to a QEMU virtual machine is labelled with
|
|
|
|
|
<code>system_u:object_r:virt_image_t</code>. In a default deployment,
|
|
|
|
|
package vendors/distributor will typically ensure that the directory
|
|
|
|
|
<code>/var/lib/libvirt/images</code> has this label, such that any
|
|
|
|
|
disk images created in this directory will automatically inherit the
|
|
|
|
|
correct labelling. If attempting to use disk images in another
|
|
|
|
|
location, the user/administrator must ensure the directory has be
|
|
|
|
|
given this requisite label. Likewise physical block devices must
|
|
|
|
|
be labelled <code>system_u:object_r:virt_image_t</code>.
|
|
|
|
|
</p>
|
|
|
|
|
<p>
|
|
|
|
|
Not all filesystems allow for labelling of individual files. In
|
|
|
|
|
particular NFS, VFat and NTFS have no support for labelling. In
|
|
|
|
|
these cases administrators must use the 'context' option when
|
|
|
|
|
mounting the filesystem to set the default label to
|
|
|
|
|
<code>system_u:object_r:virt_image_t</code>. In the case of
|
|
|
|
|
NFS, there is an alternative option, of enabling the <code>virt_use_nfs</code>
|
|
|
|
|
SELinux boolean.
|
|
|
|
|
</p>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h3><a id="securitysvirt">SELinux sVirt confinement</a></h3>
|
2009-08-19 13:17:17 +00:00
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The SELinux sVirt protection for QEMU virtual machines builds to the
|
|
|
|
|
basic level of protection, to also allow individual guests to be
|
|
|
|
|
protected from each other.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
In the sVirt model, each QEMU virtual machine runs under its own
|
|
|
|
|
confined domain, which is based on <code>system_u:system_r:svirt_t:s0</code>
|
|
|
|
|
with a unique category appended, eg, <code>system_u:system_r:svirt_t:s0:c34,c44</code>.
|
|
|
|
|
The rules are setup such that a domain can only access files which are
|
|
|
|
|
labelled with the matching category level, eg
|
|
|
|
|
<code>system_u:object_r:svirt_image_t:s0:c34,c44</code>. This prevents one
|
|
|
|
|
QEMU process accessing any file resources that are prevent to another QEMU
|
|
|
|
|
process.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
There are two ways of assigning labels to virtual machines under sVirt.
|
|
|
|
|
In the default setup, if sVirt is enabled, guests will get an automatically
|
|
|
|
|
assigned unique label each time they are booted. The libvirtd daemon will
|
|
|
|
|
also automatically relabel exclusive access disk images to match this
|
|
|
|
|
label. Disks that are marked as <shared> will get a generic
|
|
|
|
|
label <code>system_u:system_r:svirt_image_t:s0</code> allowing all guests
|
|
|
|
|
read/write access them, while disks marked as <readonly> will
|
|
|
|
|
get a generic label <code>system_u:system_r:svirt_content_t:s0</code>
|
|
|
|
|
which allows all guests read-only access.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
With statically assigned labels, the application should include the
|
|
|
|
|
desired guest and file labels in the XML at time of creating the
|
|
|
|
|
guest with libvirt. In this scenario the application is responsible
|
|
|
|
|
for ensuring the disk images & similar resources are suitably
|
|
|
|
|
labelled to match, libvirtd will not attempt any relabelling.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
2009-08-19 16:02:45 +00:00
|
|
|
If the sVirt security model is active, then the node capabilities
|
2009-08-19 13:17:17 +00:00
|
|
|
XML will include its details. If a virtual machine is currently
|
|
|
|
|
protected by the security model, then the guest XML will include
|
|
|
|
|
its assigned labels. If enabled at compile time, the sVirt security
|
|
|
|
|
model will always be activated if SELinux is available on the host
|
|
|
|
|
OS. To disable sVirt, and revert to the basic level of SELinux
|
|
|
|
|
protection (host protection only), the <code>/etc/libvirt/qemu.conf</code>
|
|
|
|
|
file can be used to change the setting to <code>security_driver="none"</code>
|
|
|
|
|
</p>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h3><a id="securitysvirtaa">AppArmor sVirt confinement</a></h3>
|
2009-10-08 14:42:05 +00:00
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
When using basic AppArmor protection for the libvirtd daemon and
|
|
|
|
|
QEMU virtual machines, the intention is to protect the host OS
|
|
|
|
|
from a compromised virtual machine process. There is no protection
|
|
|
|
|
between guests.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The AppArmor sVirt protection for QEMU virtual machines builds on
|
|
|
|
|
this basic level of protection, to also allow individual guests to
|
|
|
|
|
be protected from each other.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
In the sVirt model, if a profile is loaded for the libvirtd daemon,
|
|
|
|
|
then each <code>qemu:///system</code> QEMU virtual machine will have
|
|
|
|
|
a profile created for it when the virtual machine is started if one
|
|
|
|
|
does not already exist. This generated profile uses a profile name
|
|
|
|
|
based on the UUID of the QEMU virtual machine and contains rules
|
|
|
|
|
allowing access to only the files it needs to run, such as its disks,
|
|
|
|
|
pid file and log files. Just before the QEMU virtual machine is
|
|
|
|
|
started, the libvirtd daemon will change into this unique profile,
|
|
|
|
|
preventing the QEMU process from accessing any file resources that
|
|
|
|
|
are present in another QEMU process or the host machine.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The AppArmor sVirt implementation is flexible in that it allows an
|
|
|
|
|
administrator to customize the template file in
|
|
|
|
|
<code>/etc/apparmor.d/libvirt/TEMPLATE</code> for site-specific
|
|
|
|
|
access for all newly created QEMU virtual machines. Also, when a new
|
|
|
|
|
profile is generated, two files are created:
|
|
|
|
|
<code>/etc/apparmor.d/libvirt/libvirt-<uuid></code> and
|
|
|
|
|
<code>/etc/apparmor.d/libvirt/libvirt-<uuid>.files</code>. The
|
|
|
|
|
former can be fine-tuned by the administrator to allow custom access
|
|
|
|
|
for this particular QEMU virtual machine, and the latter will be
|
|
|
|
|
updated appropriately when required file access changes, such as when
|
|
|
|
|
a disk is added. This flexibility allows for situations such as
|
|
|
|
|
having one virtual machine in complain mode with all others in
|
|
|
|
|
enforce mode.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
While users can define their own AppArmor profile scheme, a typical
|
|
|
|
|
configuration will include a profile for <code>/usr/sbin/libvirtd</code>,
|
2020-01-30 13:57:04 +00:00
|
|
|
<code>/usr/lib/libvirt/virt-aa-helper</code> or
|
|
|
|
|
<code>/usr/libexec/virt-aa-helper</code>(a helper program which the
|
2009-10-08 14:42:05 +00:00
|
|
|
libvirtd daemon uses instead of manipulating AppArmor directly), and
|
|
|
|
|
an abstraction to be included by <code>/etc/apparmor.d/libvirt/TEMPLATE</code>
|
|
|
|
|
(typically <code>/etc/apparmor.d/abstractions/libvirt-qemu</code>).
|
|
|
|
|
An example profile scheme can be found in the examples/apparmor
|
|
|
|
|
directory of the source distribution.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
If the sVirt security model is active, then the node capabilities
|
|
|
|
|
XML will include its details. If a virtual machine is currently
|
|
|
|
|
protected by the security model, then the guest XML will include
|
|
|
|
|
its assigned profile name. If enabled at compile time, the sVirt
|
|
|
|
|
security model will be activated if AppArmor is available on the host
|
|
|
|
|
OS and a profile for the libvirtd daemon is loaded when libvirtd is
|
|
|
|
|
started. To disable sVirt, and revert to the basic level of AppArmor
|
|
|
|
|
protection (host protection only), the <code>/etc/libvirt/qemu.conf</code>
|
|
|
|
|
file can be used to change the setting to <code>security_driver="none"</code>.
|
|
|
|
|
</p>
|
|
|
|
|
|
2009-08-19 13:17:17 +00:00
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h3><a id="securityacl">Cgroups device ACLs</a></h3>
|
2009-08-19 13:17:17 +00:00
|
|
|
|
|
|
|
|
<p>
|
2019-07-17 11:56:13 +00:00
|
|
|
Linux kernels have a capability known as "cgroups" which is used
|
2009-08-19 13:17:17 +00:00
|
|
|
for resource management. It is implemented via a number of "controllers",
|
|
|
|
|
each controller covering a specific task/functional area. One of the
|
|
|
|
|
available controllers is the "devices" controller, which is able to
|
|
|
|
|
setup whitelists of block/character devices that a cgroup should be
|
|
|
|
|
allowed to access. If the "devices" controller is mounted on a host,
|
|
|
|
|
then libvirt will automatically create a dedicated cgroup for each
|
|
|
|
|
QEMU virtual machine and setup the device whitelist so that the QEMU
|
|
|
|
|
process can only access shared devices, and explicitly disks images
|
|
|
|
|
backed by block devices.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The list of shared devices a guest is allowed access to is
|
|
|
|
|
</p>
|
|
|
|
|
|
2009-11-13 23:09:20 +00:00
|
|
|
<pre>
|
|
|
|
|
/dev/null, /dev/full, /dev/zero,
|
|
|
|
|
/dev/random, /dev/urandom,
|
2019-02-18 15:13:30 +00:00
|
|
|
/dev/ptmx, /dev/kvm,
|
2019-01-21 13:48:02 +00:00
|
|
|
/dev/rtc, /dev/hpet
|
2009-11-13 23:09:20 +00:00
|
|
|
</pre>
|
2009-08-19 13:17:17 +00:00
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
In the event of unanticipated needs arising, this can be customized
|
|
|
|
|
via the <code>/etc/libvirt/qemu.conf</code> file.
|
|
|
|
|
To mount the cgroups device controller, the following command
|
|
|
|
|
should be run as root, prior to starting libvirtd
|
|
|
|
|
</p>
|
|
|
|
|
|
2009-11-13 23:09:20 +00:00
|
|
|
<pre>
|
|
|
|
|
mkdir /dev/cgroup
|
|
|
|
|
mount -t cgroup none /dev/cgroup -o devices
|
|
|
|
|
</pre>
|
2009-08-19 13:17:17 +00:00
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
libvirt will then place each virtual machine in a cgroup at
|
|
|
|
|
<code>/dev/cgroup/libvirt/qemu/$VMNAME/</code>
|
|
|
|
|
</p>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h2><a id="imex">Import and export of libvirt domain XML configs</a></h2>
|
2009-05-21 14:20:21 +00:00
|
|
|
|
|
|
|
|
<p>The QEMU driver currently supports a single native
|
|
|
|
|
config format known as <code>qemu-argv</code>. The data for this format
|
|
|
|
|
is expected to be a single line first a list of environment variables,
|
|
|
|
|
then the QEMu binary name, finally followed by the QEMU command line
|
|
|
|
|
arguments</p>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h3><a id="xmlimport">Converting from QEMU args to domain XML</a></h3>
|
2009-05-21 14:20:21 +00:00
|
|
|
|
2019-06-18 11:32:57 +00:00
|
|
|
<p>
|
2019-06-27 08:53:27 +00:00
|
|
|
<b>Note:</b> this operation is <span class="removed"> deleted as of
|
2019-06-18 11:32:57 +00:00
|
|
|
5.5.0</span> and will return an error.
|
|
|
|
|
</p>
|
2009-05-21 14:20:21 +00:00
|
|
|
<p>
|
2012-02-06 22:17:03 +00:00
|
|
|
The <code>virsh domxml-from-native</code> provides a way to
|
|
|
|
|
convert an existing set of QEMU args into a guest description
|
|
|
|
|
using libvirt Domain XML that can then be used by libvirt.
|
|
|
|
|
Please note that this command is intended to be used to convert
|
|
|
|
|
existing qemu guests previously started from the command line to
|
|
|
|
|
be managed through libvirt. It should not be used a method of
|
|
|
|
|
creating new guests from scratch. New guests should be created
|
|
|
|
|
using an application calling the libvirt APIs (see
|
|
|
|
|
the <a href="apps.html">libvirt applications page</a> for some
|
|
|
|
|
examples) or by manually crafting XML to pass to virsh.
|
2009-05-21 14:20:21 +00:00
|
|
|
</p>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h3><a id="xmlexport">Converting from domain XML to QEMU args</a></h3>
|
2009-05-21 14:20:21 +00:00
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The <code>virsh domxml-to-native</code> provides a way to convert a
|
|
|
|
|
guest description using libvirt Domain XML, into a set of QEMU args
|
2019-06-18 11:25:20 +00:00
|
|
|
that can be run manually. Note that currently the command line formatted
|
|
|
|
|
by libvirt is no longer suited for manually running qemu as the
|
|
|
|
|
configuration expects various resources and open file descriptors passed
|
|
|
|
|
to the process which are usually prepared by libvirtd.
|
2009-05-21 14:20:21 +00:00
|
|
|
</p>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h2><a id="qemucommand">Pass-through of arbitrary qemu
|
2011-12-19 18:48:04 +00:00
|
|
|
commands</a></h2>
|
|
|
|
|
|
|
|
|
|
<p>Libvirt provides an XML namespace and an optional
|
|
|
|
|
library <code>libvirt-qemu.so</code> for dealing specifically
|
|
|
|
|
with qemu. When used correctly, these extensions allow testing
|
|
|
|
|
specific qemu features that have not yet been ported to the
|
|
|
|
|
generic libvirt XML and API interfaces. However, they
|
|
|
|
|
are <b>unsupported</b>, in that the library is not guaranteed to
|
|
|
|
|
have a stable API, abusing the library or XML may result in
|
|
|
|
|
inconsistent state the crashes libvirtd, and upgrading either
|
|
|
|
|
qemu-kvm or libvirtd may break behavior of a domain that was
|
|
|
|
|
relying on a qemu-specific pass-through. If you find yourself
|
|
|
|
|
needing to use them to access a particular qemu feature, then
|
|
|
|
|
please post an RFE to the libvirt mailing list to get that
|
|
|
|
|
feature incorporated into the stable libvirt XML and API
|
|
|
|
|
interfaces.
|
|
|
|
|
</p>
|
|
|
|
|
<p>The library provides two
|
|
|
|
|
API: <code>virDomainQemuMonitorCommand</code>, for sending an
|
|
|
|
|
arbitrary monitor command (in either HMP or QMP format) to a
|
|
|
|
|
qemu guest (<span class="since">Since 0.8.3</span>),
|
|
|
|
|
and <code>virDomainQemuAttach</code>, for registering a qemu
|
|
|
|
|
domain that was manually started so that it can then be managed
|
2019-07-01 13:30:38 +00:00
|
|
|
by libvirtd (<span class="since">Since 0.9.4</span>,
|
|
|
|
|
<span class="removed">removed as of 5.5.0</span>).
|
2011-12-19 18:48:04 +00:00
|
|
|
</p>
|
|
|
|
|
<p>Additionally, the following XML additions allow fine-tuning of
|
|
|
|
|
the command line given to qemu when starting a domain
|
|
|
|
|
(<span class="since">Since 0.8.3</span>). In order to use the
|
|
|
|
|
XML additions, it is necessary to issue an XML namespace request
|
|
|
|
|
(the special <code>xmlns:<i>name</i></code> attribute) that
|
2017-10-27 21:39:00 +00:00
|
|
|
pulls in <code>http://libvirt.org/schemas/domain/qemu/1.0</code>;
|
2011-12-19 18:48:04 +00:00
|
|
|
typically, the namespace is given the name
|
|
|
|
|
of <code>qemu</code>. With the namespace in place, it is then
|
|
|
|
|
possible to add an element <code><qemu:commandline></code>
|
2020-04-22 16:02:20 +00:00
|
|
|
under <code>domain</code>, with the following sub-elements
|
2011-12-19 18:48:04 +00:00
|
|
|
repeated as often as needed:
|
2013-05-03 15:57:05 +00:00
|
|
|
</p>
|
2011-12-19 18:48:04 +00:00
|
|
|
<dl>
|
|
|
|
|
<dt><code>qemu:arg</code></dt>
|
|
|
|
|
<dd>Add an additional command-line argument to the qemu
|
|
|
|
|
process when starting the domain, given by the value of the
|
|
|
|
|
attribute <code>value</code>.
|
|
|
|
|
</dd>
|
|
|
|
|
<dt><code>qemu:env</code></dt>
|
|
|
|
|
<dd>Add an additional environment variable to the qemu
|
|
|
|
|
process when starting the domain, given with the name-value
|
|
|
|
|
pair recorded in the attributes <code>name</code>
|
|
|
|
|
and optional <code>value</code>.</dd>
|
|
|
|
|
</dl>
|
|
|
|
|
<p>Example:</p><pre>
|
2017-10-27 21:39:00 +00:00
|
|
|
<domain type='qemu' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
|
2018-03-31 14:51:14 +00:00
|
|
|
<name>QEMU-fedora-i686</name>
|
2011-12-19 18:48:04 +00:00
|
|
|
<memory>219200</memory>
|
|
|
|
|
<os>
|
|
|
|
|
<type arch='i686' machine='pc'>hvm</type>
|
|
|
|
|
</os>
|
|
|
|
|
<devices>
|
|
|
|
|
<emulator>/usr/bin/qemu-system-x86_64</emulator>
|
|
|
|
|
</devices>
|
|
|
|
|
<qemu:commandline>
|
|
|
|
|
<qemu:arg value='-newarg'/>
|
|
|
|
|
<qemu:env name='QEMU_ENV' value='VAL'/>
|
|
|
|
|
</qemu:commandline>
|
|
|
|
|
</domain>
|
2019-06-17 15:17:56 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h2><a id="xmlnsfeatures">QEMU feature configuration for testing</a></h2>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
In some cases e.g. when developing a new feature or for testing it may
|
|
|
|
|
be required to control a given qemu feature (or qemu capability) to test
|
|
|
|
|
it before it's complete or disable it for debugging purposes.
|
|
|
|
|
<span class="since">Since 5.5.0</span> it's possible to use the same
|
|
|
|
|
special qemu namespace as above
|
|
|
|
|
(<code>http://libvirt.org/schemas/domain/qemu/1.0</code>) and use
|
|
|
|
|
<code><qemu:capabilities></code> element to add
|
|
|
|
|
(<code><qemu:add capability="capname"/></code>) or remove
|
|
|
|
|
(<code><qemu:del capability="capname"/></code>) capability bits.
|
|
|
|
|
The naming of the feature bits is the same libvirt uses in the status
|
|
|
|
|
XML. Note that this feature is meant for experiments only and should
|
|
|
|
|
_not_ be used in production.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>Example:</p><pre>
|
|
|
|
|
<domain type='qemu' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
|
|
|
|
|
<name>testvm</name>
|
|
|
|
|
|
|
|
|
|
[...]
|
|
|
|
|
|
|
|
|
|
<qemu:capabilities>
|
|
|
|
|
<qemu:add capability='blockdev'/>
|
|
|
|
|
<qemu:del capability='drive'/>
|
|
|
|
|
</qemu:capabilities>
|
|
|
|
|
</domain>
|
2011-12-19 18:48:04 +00:00
|
|
|
</pre>
|
|
|
|
|
|
2017-07-26 14:52:42 +00:00
|
|
|
<h2><a id="xmlconfig">Example domain XML config</a></h2>
|
2008-04-23 17:08:31 +00:00
|
|
|
|
|
|
|
|
<h3>QEMU emulated guest on x86_64</h3>
|
|
|
|
|
|
|
|
|
|
<pre><domain type='qemu'>
|
2018-03-31 14:51:14 +00:00
|
|
|
<name>QEMU-fedora-i686</name>
|
2008-04-23 17:08:31 +00:00
|
|
|
<uuid>c7a5fdbd-cdaf-9455-926a-d65c16db1809</uuid>
|
|
|
|
|
<memory>219200</memory>
|
|
|
|
|
<currentMemory>219200</currentMemory>
|
|
|
|
|
<vcpu>2</vcpu>
|
|
|
|
|
<os>
|
|
|
|
|
<type arch='i686' machine='pc'>hvm</type>
|
|
|
|
|
<boot dev='cdrom'/>
|
|
|
|
|
</os>
|
|
|
|
|
<devices>
|
|
|
|
|
<emulator>/usr/bin/qemu-system-x86_64</emulator>
|
|
|
|
|
<disk type='file' device='cdrom'>
|
|
|
|
|
<source file='/home/user/boot.iso'/>
|
|
|
|
|
<target dev='hdc'/>
|
|
|
|
|
<readonly/>
|
|
|
|
|
</disk>
|
|
|
|
|
<disk type='file' device='disk'>
|
|
|
|
|
<source file='/home/user/fedora.img'/>
|
|
|
|
|
<target dev='hda'/>
|
|
|
|
|
</disk>
|
|
|
|
|
<interface type='network'>
|
2008-07-08 17:44:56 +00:00
|
|
|
<source network='default'/>
|
2008-04-23 17:08:31 +00:00
|
|
|
</interface>
|
|
|
|
|
<graphics type='vnc' port='-1'/>
|
|
|
|
|
</devices>
|
|
|
|
|
</domain></pre>
|
|
|
|
|
|
|
|
|
|
<h3>KVM hardware accelerated guest on i686</h3>
|
|
|
|
|
|
|
|
|
|
<pre><domain type='kvm'>
|
|
|
|
|
<name>demo2</name>
|
|
|
|
|
<uuid>4dea24b3-1d52-d8f3-2516-782e98a23fa0</uuid>
|
|
|
|
|
<memory>131072</memory>
|
|
|
|
|
<vcpu>1</vcpu>
|
|
|
|
|
<os>
|
|
|
|
|
<type arch="i686">hvm</type>
|
|
|
|
|
</os>
|
|
|
|
|
<clock sync="localtime"/>
|
|
|
|
|
<devices>
|
|
|
|
|
<emulator>/usr/bin/qemu-kvm</emulator>
|
|
|
|
|
<disk type='file' device='disk'>
|
|
|
|
|
<source file='/var/lib/libvirt/images/demo2.img'/>
|
|
|
|
|
<target dev='hda'/>
|
|
|
|
|
</disk>
|
|
|
|
|
<interface type='network'>
|
|
|
|
|
<source network='default'/>
|
|
|
|
|
<mac address='24:42:53:21:52:45'/>
|
|
|
|
|
</interface>
|
2008-12-26 13:37:53 +00:00
|
|
|
<graphics type='vnc' port='-1' keymap='de'/>
|
2008-04-23 17:08:31 +00:00
|
|
|
</devices>
|
|
|
|
|
</domain></pre>
|
|
|
|
|
|
|
|
|
|
</body>
|
|
|
|
|
</html>
|
