Install Xen With XSM FLASK Policy


The following steps are tested with Xen 4.10.0, other Xen versions with 4.8 and onward should also be fine. The tested host OSes include Ubuntu 16.04, and 18.04. Other Linux based system should be OK as long as they are compatitable with Xen hypervisor.

1. Install Prerequest Packages of Xen

Install prerequested packages of Xen. Official list of packages can be found here. For a quick install, there is a handy script for Ubuntu 18.04 and Ubuntu 16.04. You can run it to install all the dependences directly:

sudo bash


sudo bash

2. Install Xen

2.1 configure Xen

Open a terminal in the source code of Xen. Run:

cd xen-src/
./configure --enable-systemd --enable-stubdom  
2.2 enable XSM

Run the following command in the terminal:

make -C xen menuconfig

There will be a graphical interactive interface shown in the terminal. Then choose Common Features -> enable XSM, with no other sub options.

2.3 patch qemu-xen (only for Ubuntu 18.04)

Due to the upgraded libc in ubuntu 18.04, some errors would come out when compiling qemu-xen in the old release of Xen. More details. We need to upgrade qemu-xen to the lastest version to match

cd xen-src/tools/
rm -r qemu-xen/
git clone
cd -
2.4 build & install Xen
cd xen-src/
make dist -j4
# sometimes can fail with -j4, so try without it if error occurs.

sudo make install
2.5 post-install operations
sudo ldconfig

sudo systemctl enable xen-qemu-dom0-disk-backend.service
sudo systemctl enable xen-init-dom0.service
sudo systemctl enable xenconsoled.service

sudo systemctl enable xencommons
sudo systemctl enable xen-watchdog.service

3. Install XSM Policy

3.1 compile FLASK policy
cd xen-src/
make -C tools/flask/policy
3.2 copy policy to boot dir
sudo mkdir /boot/flask/
sudo cp tools/flask/policy/xenpolicy-4.10.0 /boot/flask/
cd /boot/flask
sudo ln -s xenpolicy-4.10.0 xenpolicy

4. Update Grub Scripts with Xen XSM

WARNING 1: The following steps are only tested on Ubuntu systems. Other Linux distributions should not follow these commands unless you know what you are doing.

WARNING 2: The following commands are changing your system booting parameters. Mistake operations can make your system unbootable. If you are not sure what you are doing, please first backup the files before change them.

4.1 update /etc/default/grub

We need to enable XSM flask policy in boot command parameters. Add the following line to the file /etc/default/grub (backup before change: cd /etc/default && cp grub grub.backup) :

GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=3096M,max:3096M flask=enforcing"

Change values of dom0_mem and max accordingly. They are the actual main memory you want to allocate to Domain 0 on Xen. Make sure they are the same. For the reason, see Why should I dedicate fixed amount of memory for Xen dom0.

4.2 update /etc/grub.d/20_linux_xen

This step will change grub auto generation script to load XSM policy module automatically. Under Debian systems, you can find the grub auto-generate script at /etc/grub.d/20_linux_xen. Find the correct place you need to insert the line of module /boot/flask/<xenpolicy_name>

where <xenpolicy_filename> is the XSM FLASK policy file we just compiled.

For example, on ubuntu system, the following line is changed:

--- /etc/grub.d/backup/20.linux.xen	2018-04-30 16:41:32.885068197 -0400
+++ /etc/grub.d/20_linux_xen	2018-04-30 16:42:02.273066593 -0400
@@ -138,6 +138,7 @@
     sed "s/^/$submenu_indentation/" << EOF
 	echo	'$(echo "$message" | grub_quote)'
 	module	--nounzip   ${rel_dirname}/${initrd}
+	module /boot/flaskpolicy/xenpolicy
   sed "s/^/$submenu_indentation/" << EOF
4.3 generate grub files

Run ‘sudo update-grub’. This will update your grub files (/boot/grub/grub.cfg).

4.4 check grub file

A successful update of grub should contain at least two changes in the menuentry of file /boot/grub/grub.cfg:

a) the xen kernel loading command line should have options of dom0_mem and flask. For example,

multiboot /boot/xen.gz  placeholder  dom0_mem=3096M,max:3096M flask=enforcing ${xen_rm_opts}

b). last line of the menuentry should have xenpolicy loaded. For example,

module /boot/flask/xenpolicy

The following is a complete example of a menu entry definition in /boot/grub/grub.cfg auto-generated by update-grub:

### BEGIN /etc/grub.d/20_linux_xen ###
menuentry 'Ubuntu GNU/Linux, with Xen hypervisor' --class ubuntu --class gnu-linux --class gnu --class os --class xen $menuentry_id_option '    xen-gnulinux-simple-030e940e-4663-4857-bf79-682485d1507f' {
    insmod part_msdos
    insmod ext2
    set root='hd0,msdos1'
    if [ x$feature_platform_search_hint = xy ]; then
    search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1  030e940e-4663-4857-bf79-682485d1507f
    search --no-floppy --fs-uuid --set=root 030e940e-4663-4857-b
    echo	'Loading Xen xen ...'
        if [ "$grub_platform" = "pc" -o "$grub_platform" = "" ]; then
            xen_rm_opts="no-real-mode edd=off"
    multiboot	/boot/xen.gz placeholder  dom0_mem=3096M,max:3096M flask=enforcing ${xen_rm_opts}
    echo	'Loading Linux 4.15.0-22-generic ...'
    module	/boot/vmlinuz-4.15.0-22-generic placeholder root=UUID=    030e940e-4663-4857-bf79-682485d1507f ro  quiet splash
    echo	'Loading initial ramdisk ...'
    module	--nounzip   /boot/initrd.img-4.15.0-22-generic
    module /boot/flask/xenpolicy
4.5 Reboot

Now you can reboot the system to see whether Xen is successfully installed. If successfull, you will be able to boot with Xen hypervisor on grub menu during booting.

After booted, run xl list -Z to see the result. A successful install should output something like this:

root@ubu18:~# xl list -Z
Name        ID  Mem     VCPUs   State       Time(s)     Security Label
Domain-0    0   3096    4       r-----      14753.8     system_u:system_r:dom0_t

5. Setup Xen Guest Network with WiFi or Ethernet

If WiFi on host, follow 5.1 ~ 5.3 to set up a NAT network for guest to access Internet. If Ethernet, please jump to follow 5.4.

5.1 Create a network bridge

A bridge could be created manually by running:

brctl addbr natBr
ifconfig natBr up

natBr is the name of the bridge, which is defined by yourself. To automatically create the bridge at boot time in the dom0, you can use following in your /etc/network/interfaces:

auto natBr
iface natBr inet static
bridge_ports none
bridge_stp no

The above code will create a bridge named natBr during system boot. The ip address of the bridge is Guest VMs connected to this bridge could get IP addresses with the prefix 10.0.0.*.

Once succeed, run command brctl show. The output will contain a line with defined bridge, such as:

bridge name     bridge id           STP enabled     interfaces
natBr           8000.000000000000   no      

Furthermore, ifconfig will list the bridge info as following:

natBr: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        inet6 fe80::dc2a:40ff:fe7e:566d  prefixlen 64  scopeid 0x20<link>
        ether de:2a:40:7e:56:6d  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 134  bytes 18848 (18.8 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

If you see outputs above, a bridge is successfully created. Then go to next step.

5.2 Enable forwarding and NAT

change file /etc/sysctl.conf, add (or uncomment) the line:

net.ipv4.ip_forward = 1

run $ sudo sysctl -p /etc/sysctl.conf

Enable forwarding and NAT(postrouting & masquerade) with iptables

$ sudo iptables -A FORWARD --in-interface natBr -j ACCEPT

$ sudo iptables --table nat -A POSTROUTING --out-interface <wifi_interface> -j MASQUERADE

replace <wifi_interface> with the name of your WiFi interface, such as wlps0, or lan0, etc.

5.3 In guest:

Update ( adding the bridge configs to VM). To connect the VM to the bridge ddit VM (DomU) cfg and modify the vif line (virtual interface).

vif=['bridge=natBr,ip=']   # This will connect guest to natBr with IP address

you can also leave out the ip= part and set that in the domU:

# set static ip address in domU, file /etc/network/interfaces
auto eth0
iface eth0 inet static
5.4 If Ethernet on host:

Please refer to Network Configuration Examples – Debian stype bridge configuration

6. Install Xen Guest

On Ubuntu, you can follow these steps here