xm(1)

NAME

xm - Xen management user interface

SYNOPSIS

xm subcommand [args]

DESCRIPTION

The xm program is the main interface for managing Xen guest domains. The program can be used to create, pause, and shutdown domains. It can also be used to list current domains, enable or pin VCPUs, and attach
or detach virtual block devices.

The basic structure of every xm command is almost always:

xm subcommand domain-id [OPTIONS]

Where subcommand is one of the subcommands listed below, domain-id is the numeric domain id, or the domain name (which will be internally
translated to domain id), and OPTIONS are subcommand specific options. There are a few exceptions to this rule in the cases where the subcommand in question acts on all domains, the entire machine, or directly
on the Xen hypervisor. Those exceptions will be clear for each of
those subcommands.

NOTES

All xm operations rely upon the Xen control daemon, aka xend. For any xm commands to run, xend must also be running. For this reason you should start xend as a service when your system first boots using Xen.

Most xm commands require root privileges to run due to the communications channels used to talk to the hypervisor. Running as non root
will return an error.

Most xm commands act asynchronously, so just because the xm command returned doesn't mean the action is complete. This is important, as
many operations on domains, like create and shutdown, can take considerable time (30 seconds or more) to bring the machine into a fully compliant state. If you want to know when one of these actions has finished you must poll through xm list periodically.

DOMAIN SUBCOMMANDS

The following subcommands manipulate domains directly. As stated previously, most commands take domain-id as the first parameter.

console domain-id

Attach to domain domain-id's console. If you've set up your domains to have a traditional log in console this will look much
like a normal text log in screen.

This uses the back end xenconsole service which currently only
works for para-virtual domains.

The attached console will perform much like a standard serial console, so running curses based interfaces over the console is not advised. Vi tends to get very odd when using it over this interface.

create [-c] configfile [name=value]..

The create sub command requires a config file and can optionally
take a series of name value pairs that add to or override variables defined in the config file. See xmdomain.cfg for full details of
that file format, and possible options used in either the
configfile or name=value combinations.

configfile can either be an absolute path to a file, or a relative path to a file located in /etc/xen.

Create will return as soon as the domain is started. This does not mean the guest OS in the domain has actually booted, or is available for input.

OPTIONS

-c Attache console to the domain as soon as it has started. This

is useful for determining issues with crashing domains.

EXAMPLES

with config file

xm create Fedora4

This creates a domain with the file /etc/xen/Fedora4, and
returns as soon as it is run.

without config file

xm create /dev/null ramdisk=initrd.img \

kernel=/boot/vmlinuz-2.6.12.6-xenU \
name=ramdisk nics=0 vcpus=1 \
memory=64 root=/dev/ram0

This creates the domain without using a config file (more
specifically using /dev/null as an empty config file), kernel
and ramdisk as specified, setting the name of the domain to
"ramdisk", also disabling virtual networking. (This example
comes from the xm-test test suite.)

destroy domain-id

Immediately terminate the domain domain-id. This doesn't give the domain OS any chance to react, and is the equivalent of ripping the power cord out on a physical machine. In most cases you will want to use the shutdown command instead.

domid domain-name

Converts a domain name to a domain id using xend's internal mapping.

domname domain-id

Converts a domain id to a domain name using xend's internal mapping.

help [--long]

Displays the short help message (i.e. common commands).

The --long option prints out the complete set of xm subcommands, grouped by function.

list [--long | --label] [domain-id ...]

Prints information about one or more domains. If no domains are
specified it prints out information about all domains.

An example format for the list is as follows:

Name ID Mem(MiB) VCPUs State Time(s)
Domain-0 0 98 1 r----- 5068.6
Fedora3 164 128 1 r----- 7.6
Fedora4 165 128 1 ------ 0.6
Mandrake2006 166 128 1 -b---- 3.6
Mandrake10.2 167 128 1 ------ 2.5
Suse9.2 168 100 1 ------ 1.8

Name is the name of the domain. ID the numeric domain id. Mem is the desired amount of memory to allocate to the domain (although it may not be the currently allocated amount). VCPUs is the number of virtual CPUs allocated to the domain. State is the run state (see below). Time is the total run time of the domain as accounted for by Xen.

STATES

The State field lists 6 states for a Xen domain, and which ones the current domain is in.

r - running

The domain is currently running on a CPU.

b - blocked

The domain is blocked, and not running or runnable. This can
be caused because the domain is waiting on IO (a traditional
wait state) or has gone to sleep because there was nothing else for it to do.

p - paused

The domain has been paused, usually occurring through the
administrator running xm pause. When in a paused state the domain will still consume allocated resources like memory, but will not be eligible for scheduling by the Xen hypervisor.

s - shutdown

FIXME: Why would you ever see this state?

c - crashed

The domain has crashed, which is always a violent ending. Usually this state can only occur if the domain has been configured not to restart on crash. See xmdomain.cfg for more info.

d - dying

The domain is in process of dying, but hasn't completely shutdown or crashed.

FIXME: Is this right?

LONG OUTPUT

If --long is specified, the output for xm list is not the table view shown above, but instead is an S-Expression representing
all information known about all domains asked for. This is
mostly only useful for external programs to parse the data.

Note: There is no stable guarantees on the format of this data. Use at your own risk.

LABEL OUTPUT

If --label is specified, the security labels are added to the output of xm list and the lines are sorted by the labels (ignoring case). The --long option prints the labels by default and cannot be combined with --label. See the ACCESS CONTROL SUBCOMMAND section of this man page for more information about labels.

NOTES

The Time column is deceptive. Virtual IO (network and block
devices) used by domains requires coordination by Domain0,
which means that Domain0 is actually charged for much of the
time that a DomainU is doing IO. Use of this time value to
determine relative utilizations by domains is thus very suspect, as a high IO workload may show as less utilized than a
high CPU workload. Consider yourself warned.

mem-max domain-id mem

Specify the maximum amount of memory the domain is able to use.
mem is specified in megabytes.

The mem-max value may not correspond to the actual memory used in
the domain, as it may balloon down its memory to give more back to the OS.

mem-set domain-id mem

Set the domain's used memory using the balloon driver. Because
this operation requires cooperation from the domain operating system, there is no guarantee that it will succeed.

Warning: There is no good way to know in advance how small of a mem-set will make a domain unstable and cause it to crash. Be very careful when using this command on running domains.

migrate domain-id host [OPTIONS]

Migrate a domain to another host machine. Xend must be running on
other host machine, it must be running the same version of Xen, it must have the migration TCP port open and accepting connections
from the source host, and there must be sufficient resources for
the domain to run (memory, disk, etc).

Migration is pretty complicated, and has many security implications. Please read the Xen User's Guide to ensure you understand
the ramifications and limitations on migration before attempting it in production.

OPTIONS

-l, --live

Use live migration. This will migrate the domain between hosts without shutting down the domain. See the Xen User's Guide for more information.

-r, --resource Mbs

Set maximum Mbs allowed for migrating the domain. This ensures that the network link is not saturated with migration traffic
while attempting to do other useful work.

pause domain-id

Pause a domain. When in a paused state the domain will still consume allocated resources such as memory, but will not be eligible
for scheduling by the Xen hypervisor.

reboot [OPTIONS] domain-id

Reboot a domain. This acts just as if the domain had the reboot command run from the console. The command returns as soon as it
has executed the reboot action, which may be significantly before
the domain actually reboots.

The behavior of what happens to a domain when it reboots is set by the on_reboot parameter of the xmdomain.cfg file when the domain was created.

OPTIONS

-a, --all

Reboot all domains.

-w, --wait

Wait for reboot to complete before returning. This may take a while, as all services in the domain will have to be shut down cleanly.

restore state-file

Build a domain from an xm save state file. See save for more info.

save domain-id state-file

Saves a running domain to a state file so that it can be restored
later. Once saved, the domain will no longer be running on the
system, thus the memory allocated for the domain will be free for
other domains to use. xm restore restores from this state file.

This is roughly equivalent to doing a hibernate on a running computer, with all the same limitations. Open network connections may be severed upon restore, as TCP timeouts may have expired.

shutdown [OPTIONS] domain-id

Gracefully shuts down a domain. This coordinates with the domain
OS to perform graceful shutdown, so there is no guarantee that it
will succeed, and may take a variable length of time depending on
what services must be shutdown in the domain. The command returns immediately after signally the domain unless that -w flag is used.

The behavior of what happens to a domain when it reboots is set by the on_shutdown parameter of the xmdomain.cfg file when the domain was created.

OPTIONS

-a Shutdown all domains. Often used when doing a complete shut

down of a Xen system.

-w Wait for the domain to complete shutdown before returning.

sysrq domain-id letter

Send a Magic System Request signal to the domain. For more information on available magic sys req operations, see sysrq.txt in your Linux Kernel sources.

unpause domain-id

Moves a domain out of the paused state. This will allow a previously paused domain to now be eligible for scheduling by the Xen
hypervisor.

vcpu-set domain-id vcpu-count

Enables the vcpu-count virtual CPUs for the domain in question. Like mem-set, this command can only allocate up to the maximum virtual CPU count configured at boot for the domain.

If the vcpu-count is smaller than the current number of active VCPUs, the highest number VCPUs will be hotplug removed. This may be important for pinning purposes.

Attempting to set the VCPUs to a number larger than the initially
configured VCPU count is an error. Trying to set VCPUs to < 1 will be quietly ignored.

vcpu-list [domain-id]

Lists VCPU information for a specific domain. If no domain is
specified, VCPU information for all domains will be provided.

vcpu-pin domain-id vcpu cpus

Pins the the VCPU to only run on the specific CPUs. The keyword
all can be used to apply the cpus list to all VCPUs in the domain.

Normally VCPUs can float between available CPUs whenever Xen deems a different run state is appropriate. Pinning can be used to
restrict this, by ensuring certain VCPUs can only run on certain
physical CPUs.

XEN HOST SUBCOMMANDS

dmesg [-c]

Reads the Xen message buffer, similar to dmesg on a Linux system.
The buffer contains informational, warning, and error messages created during Xen's boot process. If you are having problems with
Xen, this is one of the first places to look as part of problem
determination.

OPTIONS

-c, --clear

Clears Xen's message buffer.

info

Print information about the Xen host in name : value format. When reporting a Xen bug, please provide this information as part of the bug report.

Sample output looks as follows (lines wrapped manually to make the man page more readable):

host : talon
release : 2.6.12.6-xen0
version : #1 Mon Nov 14 14:26:26 EST 2005
machine : i686
nr_cpus : 2
nr_nodes : 1
cores_per_socket : 1
threads_per_core : 1
cpu_mhz : 696
hw_caps : 0383fbff:00000000:00000000:00000040
total_memory : 767
free_memory : 37
xen_major : 3
xen_minor : 0
xen_extra : -devel
xen_caps : xen-3.0-x86_32
xen_scheduler : credit
xen_pagesize : 4096
platform_params : virt_start=0xfc000000
xen_changeset : Mon Nov 14 18:13:38 2005 +0100

7793:090e44133d40

cc_compiler : gcc version 3.4.3 (Mandrakelinux

10.2 3.4.3-7mdk)

cc_compile_by : sdague
cc_compile_domain : (none)
cc_compile_date : Mon Nov 14 14:16:48 EST 2005
xend_config_format : 3

FIELDS

Not all fields will be explained here, but some of the less
obvious ones deserve explanation:

hw_caps

A vector showing what hardware capabilities are supported by
your processor. This is equivalent to, though more cryptic,
the flags field in /proc/cpuinfo on a normal Linux machine.

free_memory

Available memory (in MB) not allocated to Xen, or any other
domains.

xen_caps

The Xen version and architecture. Architecture values can be
one of: x86_32, x86_32p (i.e. PAE enabled), x86_64, ia64.

xen_changeset

The Xen mercurial changeset id. Very useful for determining
exactly what version of code your Xen system was built from.

log Print out the xend log. This log file can be found in

/var/log/xend.log.

top Executes the xentop command, which provides real time monitoring of

domains. Xentop is a curses interface, and reasonably self
explanatory.

SCHEDULER SUBCOMMANDS

Xen ships with a number of domain schedulers, which can be set at boot time with the sched= parameter on the Xen command line. By default credit is used for scheduling.

FIXME: we really need a scheduler expert to write up this section.

sched-credit [ -d domain-id [ -w[=WEIGHT] | -c[=CAP] ] ]

Set credit scheduler parameters. The credit scheduler is a proportional fair share CPU scheduler built from the ground up to be work conserving on SMP hosts.

Each domain (including Domain0) is assigned a weight and a cap.

PARAMETERS

WEIGHT

A domain with a weight of 512 will get twice as much CPU as a
domain with a weight of 256 on a contended host. Legal weights range from 1 to 65535 and the default is 256.

CAP The cap optionally fixes the maximum amount of CPU a domain

will be able to consume, even if the host system has idle CPU
cycles. The cap is expressed in percentage of one physical CPU: 100 is 1 physical CPU, 50 is half a CPU, 400 is 4 CPUs, etc.
The default, 0, means there is no upper cap.

sched-sedf period slice latency-hint extratime weight

Set Simple EDF (Earliest Deadline First) scheduler parameters.
This scheduler provides weighted CPU sharing in an intuitive way
and uses realtime-algorithms to ensure time guarantees. For more
information see docs/misc/sedf_scheduler_mini-HOWTO.txt in the Xen distribution.

PARAMETERS

period

The normal EDF scheduling usage in nanoseconds

slice

The normal EDF scheduling usage in nanoseconds

FIXME: these are lame, should explain more.

latency-hint

Scaled period if domain is doing heavy I/O.

extratime

Flag for allowing domain to run in extra time.

weight

Another way of setting CPU slice.

EXAMPLES

normal EDF (20ms/5ms):

xm sched-sedf <dom-id> 20000000 5000000 0 0 0

best-effort domains (i.e. non-realtime):

xm sched-sedf <dom-id> 20000000 0 0 1 0

normal EDF (20ms/5ms) + share of extra-time:

xm sched-sedf <dom-id> 20000000 5000000 0 1 0

4 domains with weights 2:3:4:2

xm sched-sedf <d1> 0 0 0 0 2
xm sched-sedf <d2> 0 0 0 0 3
xm sched-sedf <d3> 0 0 0 0 4
xm sched-sedf <d4> 0 0 0 0 2

1 fully-specified (10ms/3ms) domain, 3 other domains share available rest in 2:7:3 ratio:

xm sched-sedf <d1> 10000000 3000000 0 0 0
xm sched-sedf <d2> 0 0 0 0 2
xm sched-sedf <d3> 0 0 0 0 7
xm sched-sedf <d4> 0 0 0 0 3

VIRTUAL DEVICE COMMANDS

Most virtual devices can be added and removed while guests are running. The effect to the guest OS is much the same as any hotplug event.

BLOCK DEVICES

block-attach domain-id be-dev fe-dev mode [bedomain-id]

Create a new virtual block device. This will trigger a hotplug
event for the guest.

OPTIONS

domain-id

The domain id of the guest domain that the device will be
attached to.

be-dev

The device in the backend domain (usually domain 0) to be
exported. This can be specified as a physical partition
(phy:sda7) or as a file mounted as loopback
(file://path/to/loop.iso).

fe-dev

How the device should be presented to the guest domain. It can be specified as either a symbolic name, such as /dev/hdc, for
common devices, or by device id, such as 0x1400 (/dev/hdc
device id in hex).

mode

The access mode for the device from the guest domain. Supported modes are w (read/write) or r (read-only).

bedomain-id

The back end domain hosting the device. This defaults to
domain 0.

EXAMPLES

Mount an ISO as a Disk

xm block-attach guestdomain file://path/to/dsl-2.0RC2.iso
/dev/hdc ro

This will mount the dsl ISO as /dev/hdc in the guestdomain as a read only device. This will probably not be detected as a CDROM by the guest, but mounting /dev/hdc manually will work.

block-detach domain-id devid [--force]

Detach a domain's virtual block device. devid may be the symbolic name or the numeric device id given to the device by domain 0. You will need to run xm block-list to determine that number.

Detaching the device requires the cooperation of the domain. If
the domain fails to release the device (perhaps because the domain is hung or is still using the device), the detach will fail. The
--force parameter will forcefully detach the device, but may cause IO errors in the domain.

block-list [-l|--long] domain-id

List virtual block devices for a domain. The returned output is
formatted as a list or as an S-Expression if the --long option was given.

NETWORK DEVICES

network-attach domain-id [script=scriptname] [ip=ipaddr] [mac=macaddr] [bridge=bridge-name] [backend=bedomain-id]

Creates a new network device in the domain specified by domain-id. It takes the following optional options:

OPTIONS

script=scriptname

Use the specified script name to bring up the network.
Defaults to the default setting in xend-config.sxp for vifscript.

ip=ipaddr

Passes the specified IP Address to the adapter on creation.

FIXME: this currently appears to be broken. I'm not sure under what circumstances this should actually work.

mac=macaddr

The MAC address that the domain will see on its Ethernet
device. If the device is not specified it will be randomly
generated with the 00:16:3e vendor id prefix.

bridge=bridge-name

The name of the bridge to attach the vif to, in case you have
more than one. This defaults to xenbr0.

backend=bedomain-id

The backend domain id. By default this is domain 0.

network-detach domain-id devid

Removes the network device from the domain specified by domain-id. devid is the virtual interface device number within the domain (i.e. the 3 in vif22.3).

FIXME: this is currently broken. Network devices aren't completely removed from domain 0.

network-list [-l|--long]> domain-id

List virtual network interfaces for a domain. The returned output is formatted as a list or as an S-Expression if the --long option was given.

VIRTUAL TPM DEVICES

vtpm-list [-l|--long] domain-id

Show the virtual TPM device for a domain. The returned output is
formatted as a list or as an S-Expression if the --long option was given.

VNET COMMANDS

The Virtual Network interfaces for Xen.

FIXME: This needs a lot more explanation, or it needs to be ripped out entirely.

vnet-list [-l|--long]

List vnets.

vnet-create config

Create a vnet from a config file.

vnet-delete vnetid

Delete a vnet.

ACCESS CONTROL SUBCOMMANDS

Access Control in Xen consists of two components: (i) The Access Control Policy (ACP) defines security labels and access rules based on
these labels. (ii) The Access Control Module (ACM) makes access control decisions by interpreting the policy when domains require to communicate or to access resources. The Xen access control has sufficient
mechanisms in place to enforce the access decisions even against maliciously acting user domains (mandatory access control).

Access rights for domains in Xen are determined by the domain security label only and not based on the domain Name or ID. The ACP specifies
security labels that can then be assigned to domains and resources.
Every domain must be assigned exactly one security label, otherwise
access control decisions could become indeterministic. ACPs are distinguished by their name, which is a parameter to most of the subcommands described below. Currently, the ACP specifies two ways to interpret
labels:

(1) Simple Type Enforcement: Labels are interpreted to decide access of domains to communication means and virtual or physical resources. Communication between domains as well as access to resources are forbidden by default and can only take place if they are explicitly allowed by
the security policy. The proper assignment of labels to domains controls the sharing of information (directly through communication or
indirectly through shared resources) between domains. This interpretation allows to control the overt (intended) communication channels in
Xen.

(2) Chinese Wall: Labels are interpreted to decide which domains can
co-exist (be run simultaneously) on the same system. This interpretation allows to prevent direct covert (unintended) channels and mitigates risks caused by imperfect core domain isolation (trade-off
between security and other system requirements). For a short introduction to covert channels, please refer to http://www.multicians.org/timing-chn.html.

The following subcommands help you to manage security policies in Xen
and to assign security labels to domains. To enable access control
security in Xen, you must compile Xen with ACM support enabled as
described under "Configuring Security" below. There, you will find also examples of each subcommand described here.

setpolicy ACM policy

Makes the given ACM policy available to xend as a xend-managed policy. The policy is compiled and a mapping (.map) as well as a binary (.bin) version of the policy is created. The policy is
loaded and the system's bootloader is prepared to boot the system
with this policy the next time it is started.

policy is a dot-separated list of names. The last part is the file name pre-fix for the policy XML file. The preceding name parts are translated into the local path pointing to the policy XML file relative to the global policy root directory (/etc/xen/acm-security/policies). For example, example.chwall_ste.client_v1 denotes
the policy file example/chwall_ste/client_v1-security_policy.xml
relative to the global policy root directory.

resetpolicy

Reset the system's policy to the default state where the DEFAULT
policy is loaded and enforced. This operation may fail if for example guest VMs are running and and one of them uses a different
label than what Domain-0 does. It is best to make sure that no
guests are running before issuing this command.

getpolicy [--dumpxml]

Displays information about the current xend-managed policy, such as name and type of the policy, the uuid xend has assigned to it on
the local system, the version of the XML representation and the
status of the policy, such as whether it is currently loaded into
Xen or whether the policy is automatically loaded during system
boot. With the --dumpxml option, the XML representation of the policy is displayed.

dumppolicy

Prints the current security policy state information of Xen.

labels [policy] [type=dom|res|any]

Lists all labels of a type (domain, resource, or both) that are defined in the policy. Unless specified, the default policy is the currently enforced access control policy. The default for type is 'dom'. The labels are arranged in alphabetical order.

addlabel label dom configfile [policy] addlabel label mgt domain name [policy type:policy] addlabel label res resource [policy] addlabel label vif-idx domain name [policy type:policy]

Adds the security label with name label to a domain configfile (dom), a Xend-managed domain (mgt), to the global resource label
file for the given resource (res), or to a managed domain's virtual network interface (vif) that is specified by its index. Unless
specified, the default policy is the currently enforced access control policy. This subcommand also verifies that the policy definition supports the specified label name.

The only policy type that is currently supported is ACM.

rmlabel dom configfile
rmlabel mgt domain name
rmlabel res resource
rmlabel vif-idx domain name

Works the same as the addlabel command (above), except that this command will remove the label from the domain configfile (dom), a Xend-managed domain (mgt), the global resource label file (res), or a managed domain's network interface (vif).

getlabel dom configfile
getlabel mgt domain name
getlabel res resource
getlabel vif-idx domain name

Shows the label for a domain's configuration in the given configfile, a xend-managed domain (mgt), a resource, or a managed domain's network interface (vif).

resources

Lists all resources in the global resource label file. Each
resource is listed with its associated label and policy name.

dry-run configfile

Determines if the specified configfile describes a domain with a valid security configuration for type enforcement. The test shows
the policy decision made for each resource label against the domain label as well as the overall decision.

CONFIGURING SECURITY

In xen_source_dir/Config.mk set the following parameter:

XSM_ENABLE ?= y
ACM_SECURITY ?= y

Then recompile and install xen and the security tools and then
reboot:

cd xen_source_dir; make clean; make install
reboot into Xen

RESETTING THE SYSTEM'S SECURITY

To set the system's security policy enforcement into its default
state, the follow command can be issued. Make sure that no guests
are running while doing this.

xm resetpolicy

After this command has successfully completed, the system's DEFAULT policy is enforced.

SETTING A SECURITY POLICY

This step sets the system's policy and automatically loads it into Xen for enforcement.

xm setpolicy ACM example.client_v1

LISTING SECURITY LABELS

This subcommand shows all labels that are defined and which can be attached to domains.

xm labels example.client_v1 type=dom

will print for our example policy:

dom_BoincClient
dom_Fun
dom_HomeBanking
dom_NetworkDomain
dom_StorageDomain
dom_SystemManagement

ATTACHING A SECURITY LABEL TO A DOMAIN

The addlabel subcommand can attach a security label to a domain configuration file, here a HomeBanking label. The example policy
ensures that this domain does not share information with other nonhomebanking user domains (i.e., domains labeled as dom_Fun or
dom_Boinc) and that it will not run simultaneously with domains
labeled as dom_Fun.

We assume that the specified myconfig.xm configuration file actually instantiates a domain that runs workloads related to
home-banking, probably just a browser environment for online-banking.

xm addlabel dom_HomeBanking dom myconfig.xm

The very simple configuration file might now look as printed below. The addlabel subcommand added the access_control entry at the end of the file, consisting of a label name and the policy that specifies this label name:

kernel = "/boot/vmlinuz-2.6.16-xen"
ramdisk="/boot/U1_home_banking_ramdisk.img"
memory = 164
name = "homebanking"
vif = [ '' ]
dhcp = "dhcp"
access_control = ['policy=example.chwall_ste.client_v1,

label=dom_HomeBanking']

Security labels must be assigned to domain configurations because
these labels are essential for making access control decisions as
early as during the configuration phase of a newly instantiated
domain. Consequently, a security-enabled Xen hypervisor will only
start domains that have a security label configured and whose security label is consistent with the currently enforced policy. Otherwise, starting the domain will fail with the error condition "operation not permitted".

ATTACHING A SECURITY LABEL TO A XEND-MANAGED DOMAIN

The addlabel subcommand supports labeling of domains that are managed by xend. This includes domains that are currently running,
such as for example Domain-0, or those that are in a dormant state. Depending on the state of the system, it is possible that the new
label is rejected. An example for a reason for the rejection of the relabeling of a domain would be if a domain is currently allowed to access its labeled resources but due to the new label would be prevented from accessing one or more of them.

xm addlabel dom_Fun mgt Domain-0

This changes the label of Domain-0 to dom_Fun under the condition
that this new label of Domain-0 would not prevent any other domain from accessing its resources that are provided through Domain-0,
such as for example network or block device access.

ATTACHING A SECURITY LABEL TO A RESOURCE

The addlabel subcommand can also be used to attach a security label to a resource. Following the home banking example from above, we
can label a disk resource (e.g., a physical partition or a file) to make it accessible to the home banking domain. The example policy
provides a resource label, res_LogicalDiskPartition1(hda1), that is compatible with the HomeBanking domain label.

xm addlabel "res_LogicalDiskPartition1(hda1)" res phy:hda6

After labeling this disk resource, it can be attached to the domain by adding a line to the domain configuration file. The line below
attaches this disk to the domain at boot time.

disk = [ 'phy:hda6,sda2,w' ]

Alternatively, the resource can be attached after booting the
domain by using the block-attach subcommand.

xm block-attach homebanking phy:hda6 sda2 w

Note that labeled resources cannot be used when security is turned off. Any attempt to use labeled resources with security turned off will result in a failure with a corresponding error message. The
solution is to enable security or, if security is no longer
desired, to remove the resource label using the rmlabel subcommand.

STARTING AND LISTING LABELED DOMAINS

xm create myconfig.xm

xm list --label

Name ID ... Time(s) Label
homebanking 23 ... 4.4 dom_HomeBanking
Domain-0 0 ... 2658.8 dom_SystemManagement

LISTING LABELED RESOURCES

xm resources

phy:hda6

type: ACM

policy: example.chwall_ste.client_v1
label: res_LogicalDiskPartition1(hda1)

file:/xen/disk_image/disk.img

type: ACM

policy: example.chwall_ste.client_v1
label: res_LogicalDiskPartition2(hda2)

POLICY REPRESENTATIONS

We distinguish three representations of the Xen access control policy: the source XML version, its binary counterpart, and a mapping representation that enables the tools to deterministically translate back and forth between label names of the XML policy and label identifiers of the binary policy. All three versions must be kept
consistent to achieve predictable security guarantees.

The XML version is the version that users are supposed to create or change, either by manually editing the XML file or by using the Xen policy generation tool (xensec_gen). After changing the XML file, run the setpolicy subcommand to ensure that the new policy is available to xend. Use, for example, the subcommand activatepolicy to activate the changes during the next system reboot.

The binary version of the policy is derived from the XML policy by tokenizing the specified labels and is used inside Xen only. It is created with the setpolicy subcommand. Essentially, the binary version is much more compact than the XML version and is easier to
evaluate during access control decisions.

The mapping version of the policy is created during the XML-tobinary policy translation (setpolicy) and is used by xend and the management tools to translate between label names used as input to the tools and their binary identifiers (ssidrefs) used inside Xen.

SEE ALSO

xmdomain.cfg(5), xentop(1)

AUTHOR

Sean Dague <sean at dague dot net>
Daniel Stekloff <dsteklof at us dot ibm dot com>
Reiner Sailer <sailer at us dot ibm dot com>
Stefan Berger <stefanb at us dot ibm dot com>

BUGS

xen-unstable 2008-01-26 xm(1)