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cbe6ad9034
This change enables to run cloud-hypervisor VMM using a non-root user when rootless flag is set true in the configuration Fixes: #2567 Signed-off-by: Feng Wang <fwang@confluent.io>
33 lines
2.1 KiB
Markdown
33 lines
2.1 KiB
Markdown
## Introduction
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To improve security, Kata Container supports running the VMM process (QEMU and cloud-hypervisor) as a non-`root` user.
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This document describes how to enable the rootless VMM mode and its limitations.
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## Pre-requisites
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The permission and ownership of the `kvm` device node (`/dev/kvm`) need to be configured to:
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```
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$ crw-rw---- 1 root kvm
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```
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use the following commands:
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```
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$ sudo groupadd kvm -r
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$ sudo chown root:kvm /dev/kvm
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$ sudo chmod 660 /dev/kvm
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```
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## Configure rootless VMM
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By default, the VMM process still runs as the root user. There are two ways to enable rootless VMM:
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1. Set the `rootless` flag to `true` in the hypervisor section of `configuration.toml`.
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2. Set the Kubernetes annotation `io.katacontainers.hypervisor.rootless` to `true`.
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## Implementation details
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When `rootless` flag is enabled, upon a request to create a Pod, Kata Containers runtime creates a random user and group (e.g. `kata-123`), and uses them to start the hypervisor process.
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The `kvm` group is also given to the hypervisor process as a supplemental group to give the hypervisor process access to the `/dev/kvm` device.
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Another necessary change is to move the hypervisor runtime files (e.g. `vhost-fs.sock`, `qmp.sock`) to a directory (under `/run/user/[uid]/`) where only the non-root hypervisor has access to.
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## Limitations
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1. Only the VMM process is running as a non-root user. Other processes such as Kata Container shimv2 and `virtiofsd` still run as the root user.
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2. Currently, this feature is only supported in QEMU and cloud-hypervisor. For firecracker, you can use jailer to run the VMM process with a non-root user.
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3. Certain features will not work when rootless VMM is enabled, including:
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1. Passing devices to the guest (`virtio-blk`, `virtio-scsi`) will not work if the non-privileged user does not have permission to access it (leading to a permission denied error). A more permissive permission (e.g. 666) may overcome this issue. However, you need to be aware of the potential security implications of reducing the security on such devices.
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2. `vfio` device will also not work because of permission denied error. |