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With landlock enabled, the vmdk disk path representing the descriptor file is added to allowed path. However, this is a plain text file which points to actual data blobs called extents. The extent paths are not allowed and must be explicitly passed via landlock-rules path. Signed-off-by: Sumedh Alok Sharma <sumsharma@microsoft.com>
131 lines
4.0 KiB
Markdown
131 lines
4.0 KiB
Markdown
# Sandboxing using Landlock
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Landlock is a lightweight mechanism to allow unprivileged applications to
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sandbox themselves.
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During initial stages of running, applications can define the set of resources
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(mostly files) they need to access during their lifetime. All such rules are
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used to create a ruleset. Once the ruleset is applied, the process cannot access
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any resources outside of the ruleset during its lifetime, even if it were
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compromised.
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Under the scope of `read` and `write` access, Landlock currently allows some
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additional accesses (eg: for now, access to extended file attributes is always
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allowed). Eventually, Landlock will only allow accesses similar to Unix
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permissions.
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## Host Setup
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Landlock should be enabled in host kernel to use it with cloud-hypervisor.
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Please follow [Kernel-Support](https://docs.kernel.org/userspace-api/landlock.html#kernel-support) link to enable Landlock on Host kernel.
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Landlock support can be checked with the following command:
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```
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$ sudo dmesg | grep -w landlock
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[ 0.000000] landlock: Up and running.
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```
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Linux kernel confirms Landlock support with above message in dmesg.
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## Enable Landlock
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At the time of enabling Landlock, Cloud-Hypervisor process needs the complete
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list of files it accesses over its lifetime. So, Landlock is enabled at the
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`vm_create` stage of guest boot.
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### Command Line
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Append `--landlock` to Cloud-Hypervisor's command line to enable Landlock
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support.
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If you expect guest to access additional paths after it boots
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(ex: during hotplug), those paths can be passed using `--landlock-rules` command
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line parameter.
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### API
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Landlock can also be enabled during `vm.create` request by passing a config like below:
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```
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{
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...
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"landlock_enable": true,
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"landlock_rules": [
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{
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"path": "/tmp/disk1",
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"access": "rw"
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},
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{
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"path": "/tmp/disk2",
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"access": "rw"
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}
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]
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...
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}
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```
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### Multi-file disk formats (VMDK)
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For most block backends (raw, qcow2, VHD) including existing VMDK, landlock
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grants access to the `--disk path=` path value.
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For a Flat VMDK, its `path=` points at a small text descriptor whose
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data lives in one or more separate extent files. Granting only the descriptor
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currently leaves those extents unreachable under landlock.
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The process launching Cloud-Hypervisor must grant these extent paths explicitly
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via `--landlock-rules` (or the `landlock_rules` API field). The descriptor file's
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extent section mentions the extent file path which can be either:
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- relative (the `qemu-img` default) in which case the full path includes the descriptor
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file's parent directory
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- absolute, which can live inside the descriptor file's parent directory or in another
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directory
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For example, a containerd/Kata deployment where the read-only image
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layer resides under `/var/lib/containerd` should add that path:
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```
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--landlock-rules path="/var/lib/containerd",access="rw"
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```
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## Usage Examples
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To enable Landlock:
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```
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./cloud-hypervisor \
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--kernel ./linux-cloud-hypervisor/arch/x86/boot/compressed/vmlinux.bin \
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--disk path=focal-server-cloudimg-amd64.raw path=/tmp/ubuntu-cloudinit.img \
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--cmdline "console=hvc0 root=/dev/vda1 rw" \
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--cpus boot=4 \
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--memory size=1024M \
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--net "tap=,mac=,ip=,mask=" \
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--landlock
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```
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Hotplugging any new file-backed resources to above guest will result in
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**Permission Denied** error.
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To enable Landlock with hotplug support:
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```
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./cloud-hypervisor \
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--api-socket /tmpXXXX/ch.socket \
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--kernel ./linux-cloud-hypervisor/arch/x86/boot/compressed/vmlinux.bin \
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--disk path=focal-server-cloudimg-amd64.raw path=/tmp/ubuntu-cloudinit.img \
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--cmdline "console=hvc0 root=/dev/vda1 rw" \
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--cpus boot=4 \
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--memory size=1024M \
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--net "tap=,mac=,ip=,mask=" \
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--landlock \
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--landlock-rules path="/path/to/hotplug1",access="rw" path="/path/to/hotplug2",access="rw"
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./ch-remote --api-socket /tmpXXXX/ch.socket \
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add-disk "path=/path/to/hotplug/blk.raw"
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```
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`--landlock-rules` accepts file or directory paths among its options.
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# References
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* https://landlock.io/
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