# KVM-Kernel Example

The source code are examples on my blog: [Learning KVM - implement your own kernel](https://david942j.blogspot.com/2018/10/note-learning-kvm-implement-your-own.html).

I've described how to implement a KVM-based hypervisor and the key points to implement a kernel on my blog.
You can leave comments in the blog or file issues here if you have questions or find any bug.

## Dir

### Hypervisor

The KVM-based hypervisor, its role is like qemu-system.

### Kernel

A extremely simple kernel, supports few syscalls.

### User

Simple ELF(s) for testing our kernel.
Pre-built user program was provided, and you can re-generate by the following commands:
```sh
$ pip3 install pwntools
$ user/gen.py
```
NOTE: You have to install Python 3.x in advance.

## Setup

### Check KVM support

Check if your CPU supports virtualization:
```
$ egrep '(vmx|svm)' /proc/cpuinfo
```
NOTE: CPUs in a VM might not support virtualization (i.e. no nested virtualization).
For example, EC2 on AWS doesn't support using KVM.

### Install KVM device

Check if the KVM device exists:
```
$ ls -la /dev/kvm
```

If `/dev/kvm` is not found, you can enable it (on Ubuntu) with:
```
$ sudo apt install qemu-kvm
```

If you are not root, you need to add yourself into the `kvm` group to have permission for accessing `/dev/kvm`.
```
$ sudo usermod -a -G kvm `whoami`
```
Remember to logout and login to have the group changing effective.


## How to run

```sh
$ git clone https://github.com/david942j/kvm-kernel-example
$ cd kvm-kernel-example && make
$ hypervisor/hypervisor.elf kernel/kernel.bin user/orw.elf /etc/os-release
# NAME="Ubuntu"
# VERSION="18.04.1 LTS (Bionic Beaver)"
# ID=ubuntu
# ID_LIKE=debian
# PRETTY_NAME="Ubuntu 18.04.1 LTS"
# VERSION_ID="18.04"
# HOME_URL="https://www.ubuntu.com/"
# SUPPORT_URL="https://help.ubuntu.com/"
# BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
# PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
# VERSION_CODENAME=bionic
# UBUNTU_CODENAME=bionic
# +++ exited with 0 +++
```

### Environment

I only tested the code on Ubuntu 18.04, but I expect it to work on all KVM-supported x86 Linux distributions. Please file an issue if you find it's not true.