Like other services under the protection of SELinux, sVirt uses process-based mechanisms and restrictions to provide an extra layer of security over guest instances. Under typical use, you should not even notice that sVirt is working in the background. This section describes the labelling features of sVirt.
As shown in the following output, when using sVirt, each Virtual Machine (VM) process is labelled and runs with a dynamically generated level. Each process is isolated from other VMs with different levels:
# ps -eZ | grep qemu
system_u:system_r:svirt_t:s0:c87,c520 27950 ? 00:00:17 qemu-kvm
system_u:system_r:svirt_t:s0:c639,c757 27989 ? 00:00:06 qemu-system-x86
The actual disk images are automatically labelled to match the processes, as shown in the following output:
# ls -lZ /var/lib/libvirt/images/*
system_u:object_r:svirt_image_t:s0:c87,c520 image1
The following table outlines the different labels that can be assigned when using sVirt:
Table 7.1. sVirt Labels
| Type |
SELinux Context |
Description |
| Virtual Machine Processes |
system_u:system_r:svirt_t:MCS1 |
MCS1 is a randomly selected MCS field. Currently approximately 500,000 labels are supported. |
| Virtual Machine Image |
system_u:object_r:svirt_image_t:MCS1 |
Only svirt_t processes with the same MCS fields are able to read/write these image files and devices. |
| Virtual Machine Shared Read/Write Content |
system_u:object_r:svirt_image_t:s0 |
All svirt_t processes are allowed to write to the svirt_image_t:s0 files and devices. |
| Virtual Machine Shared Shared Read Only content |
system_u:object_r:svirt_content_t:s0 |
All svirt_t processes are able to read files/devices with this label. |
| Virtual Machine Image |
system_u:object_r:virt_content_t:s0 |
System default label used when an image exits. No svirt_t virtual processes are allowed to read files/devices with this label. |
It is also possible to perform static labeling when using sVirt. Static labels allow the administrator to select a specific label, including the MCS/MLS field, for a virtual machine. Administrators who run statically-labeled virtual machines are responsible for setting the correct label on the image files. The virtual machine will always be started with that label, and the sVirt system will never modify the label of a statically-labelled virtual machine's content. This allows the sVirt component to run in an MLS environment. You can also run multiple virtual machines with different sensitivity levels on a system, depending on your requirements.
