When you are running Gentoo with SELinux enabled, you will be running with a particular policy type, which you can devise from either /etc/selinux/config or from the output of the sestatus command. As a user on our IRC channel had some issues converting his strict-policy system to mcs, I thought about testing it out myself. Below are the steps I did and the reasoning why (and I will update the docs to reflect this accordingly).

Let's first see if the type I am running at this moment is indeed strict, and that the mcs type is defined in the POLICY_TYPES variable. This is necessary because the sec-policy/selinux-* packages will then build the policy modules for the other types referenced in this variable as well.

test ~ # sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             strict
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              disabled
Policy deny_unknown status:     denied
Max kernel policy version:      28

test ~ # grep POLICY_TYPES /etc/portage/make.conf
POLICY_TYPES="targeted strict mcs"

If you notice that this is not the case, update the POLICY_TYPES variable and rebuild all SELinux policy packages using emerge \$(qlist -IC sec-policy) first.

Let's see if I indeed have policies for the other types available and that they are recent (modification date):

test ~ # ls -l /etc/selinux/*/policy
/etc/selinux/mcs/policy:
total 408
-rw-r--r--. 1 root root 417228 Dec 19 21:01 policy.27

/etc/selinux/strict/policy:
total 384
-rw-r--r--. 1 root root 392168 Dec 19 21:15 policy.27

/etc/selinux/targeted/policy:
total 396
-rw-r--r--. 1 root root 402931 Dec 19 21:01 policy.27

Great, we're now going to switch to permissive mode and edit the SELinux configuration file to reflect that we are going to boot (later) into the mcs policy. Only change the type - I will not boot in permissive mode so the SELINUX=enforcing can stay.

test ~ # setenforce 0

test ~ # vim /etc/selinux/config
[... set SELINUXTYPE=mcs ...]

You can run sestatus to verify the changes, but be aware that - while the command does say that the mcs policy is loaded, this is not the case. The mcs policy is just defined as the policy to load:

test ~ # sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             mcs
Current mode:                   permissive
Mode from config file:          enforcing
Policy MLS status:              disabled
Policy deny_unknown status:     denied
Max kernel policy version:      28

So let's load the mcs policy shall we?

test ~ # cd /usr/share/selinux/mcs/
test mcs # semodule -b base.pp -i $(ls *.pp | grep -v base | grep -v unconfined)

Next we are going to relabel all files on the file system, because the mcs policy adds in another component in the context (a sensitivity label - always set to 0 for mcs). We will also re-do the setfiles steps done initially while setting up SELinux on our system. This is because we need to relabel files that are "hidden" from the current file system because other file systems are mounted on top of it.

test mcs # rlpkg -a -r
Relabeling filesystem types: btrfs ext2 ext3 ext4 jfs xfs
Scanning for shared libraries with text relocations...
0 libraries with text relocations, 0 not relabeled.
Scanning for PIE binaries with text relocations...
0 binaries with text relocations detected.

test mcs # mount -o bind / /mnt/gentoo
test mcs # setfiles -r /mnt/gentoo /etc/selinux/mcs/contexts/files/file_contexts /mnt/gentoo/dev
test mcs # setfiles -r /mnt/gentoo /etc/selinux/mcs/contexts/files/file_contexts /mnt/gentoo/lib64
test mcs # umount /mnt/gentoo

Finally, edit /etc/fstab and change all rootcontext= parameters to include a trailing :s0, otherwise the root contexts of these file systems will be illegal (in the mcs-sense) as they do not contain the sensitivity level information.

test mcs # vim /etc/fstab
[... edit rootcontext's to now include ":s0" ...]

There ya go. Now reboot and notice that all is okay, and we're running with the mcs policy loaded.

test ~ # id -Z
root:sysadm_r:sysadm_t:s0-s0:c0.c1023
test ~ # sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             mcs
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     denied
Max kernel policy version:      28

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