cloud-hypervisor/docs/landlock.md

Sandboxing using Landlock

Landlock is a lightweight mechanism to allow unprivileged applications to sandbox themselves.

During initial stages of running, applications can define the set of resources (mostly files) they need to access during their lifetime. All such rules are used to create a ruleset. Once the ruleset is applied, the process cannot access any resources outside of the ruleset during its lifetime, even if it were compromised.

Under the scope of read and write access, Landlock currently allows some additional accesses (eg: for now, access to extended file attributes is always allowed). Eventually, Landlock will only allow accesses similar to Unix permissions.

Host Setup

Landlock should be enabled in Host kernel to use it with cloud-hypervisor. Please following Kernel-Support link to enable Landlock on Host kernel.

Landlock support can be checked with following command:

$ sudo dmesg | grep -w  landlock
[    0.000000] landlock: Up and running.

Linux kernel confirms Landlock support with above message in dmesg.

Implementation Details

To enable Landlock, Cloud-Hypervisor process needs the full list of files it needs to access over its lifetime. Most of these files are received as VM Configuration (struct VmConfig). Landlock is enabled in vm_create stage, as this is the earliest stage in guest boot sequence which has access to guest's VM Configuration.

Enable Landlock

Append --landlock to Cloud-Hypervisor's command line to enable Landlock support.

If you expect guest to access additional paths after it boots (ex: during hotplug), those paths can be passed using --landlock-rules command line parameter.

Usage Examples

To enable Landlock:

./cloud-hypervisor \
	--kernel ./linux-cloud-hypervisor/arch/x86/boot/compressed/vmlinux.bin \
	--disk path=focal-server-cloudimg-amd64.raw path=/tmp/ubuntu-cloudinit.img \
	--cmdline "console=hvc0 root=/dev/vda1 rw" \
	--cpus boot=4 \
	--memory size=1024M \
	--net "tap=,mac=,ip=,mask=" \
	--landlock

Hotplugging any new file-backed resources to above guest will result in Permission Denied error.

To enable Landlock with hotplug support:

./cloud-hypervisor \
	--api-socket /tmpXXXX/ch.socket \
	--kernel ./linux-cloud-hypervisor/arch/x86/boot/compressed/vmlinux.bin \
	--disk path=focal-server-cloudimg-amd64.raw path=/tmp/ubuntu-cloudinit.img \
	--cmdline "console=hvc0 root=/dev/vda1 rw" \
	--cpus boot=4 \
	--memory size=1024M \
	--net "tap=,mac=,ip=,mask=" \
	--landlock \
	--landlock-rules path="/path/to/hotplug1",access="rw" path="/path/to/hotplug2",access="rw"

./ch-remote --api-socket /tmpXXXX/ch.socket \
	add-disk "path=/path/to/hotplug/blk.raw"

--landlock-rules accepts file or directory paths among its options.

References

• https://landlock.io/