bondey / kvm-vmi

KVM-based Virtual Machine Introspection

kvm-vmi

KVM-based Virtual Machine Instrospection.

Table of Contents

• Overview
• Install
  • Vagrant
  • Manually
• References
• Maintainers
• Contributing
• License

Overview

This project adds virtual machine introspection to the KVM hypervisor to monitor a running virtual machine without a guest agent.

This project is divided into 4 components:

• kvm: linux kernel with vmi patches for KVM
• qemu: patched to allow introspection
• nitro: userland library which receives events, introspects the virtual machine state, and fills the semantic gap
• libvmi: virtual machine instrospection library with unified API across Xen and KVM

At the moment, 2 versions of VMI patches are available for QEMU/KVM in this repository:

1 - Nitro (legacy)

KVM-VMI started as an improved fork of Nitro, a set of VMI patches for QEMU/KVM to intercept system calls and rebuild the execution context.

Nitro is the name of the userland component that will receive and interpret the syscalls, as well as the name of the set of patches for QEMU/KVM.

Corresponding submodule branches:

• kvm: vmi
• qemu: vmi
• nitro: master
• libvmi: nitro

(Sorry for the confusing branches naming...)

Details:

Once the traps are set, the VM will be in a "paused" state and go back to the hypervisor on every system call. In details, the traps are working directly at the instruction level, on syscall and sysret, which means that you can also stop the VM when the system call returns from the kernel.

When the VM is "paused", some introspection can be done by reading or writing into the memory. Therefore it is possible to reconstruct VM state and understand the system call context (process name, system call name).

Furthermore, we are able to decode the system call parameters and display what file is being created (in the case of NtCreateFile, for Windows only).

A hooking API allows you to define callbacks on top of the system calls you intercept:

NtCreateFile

def enter_NtCreateFile(syscall):
    DesiredAccess = syscall.args[1]
    object_attributes = syscall.args[2]
    obj = ObjectAttributes(object_attributes, syscall.process)
    buffer = obj.ObjectName.Buffer
    access = FileAccessMask(DesiredAccess)
    syscall.hook = {
        'object_name': buffer,
        'access': access.rights
    }

Resulting in this output:

[
    {
        "event": {
            "cr3": "0x76f9e000",
            "vcpu": 0,
            "rax": "0x52",
            "direction": "enter",
            "type": "syscall"
        },
        "name": "NtCreateFile",
        "process": {
            "pid": 2344,
            "name": "powershell.exe"
        },
        "hook": {
            "object_name": "\\??\\C:\\Program Files\\Windows Sidebar\\Gadgets\\PicturePuzzle.Gadget\\en-US\\gadget.xml",
            "access": [
                "SYNCHRONIZE",
                "GENERIC_READ",
                "FILE_READ_ATTRIBUTES"
            ]
        }
    },
]

2 - KVMI

A complete set of VMI APIs proposed by BitDefender

This is where the current effort is focused on.

Corresponding submodule branches:

• kvm: kvmi
• qemu: kvmi
• nitro: kvmi
• libvmi: kvmi

Install

Vagrant (recommended)

Go to the vagrant/ sub-directory to install a development environment for kvm-vmi

Manually

Unfortunately, it is not possible to compile the KVM modules as an out-of-tree build. You will have to compile and install a new kernel along with the new modules.

This is only valid for the Nitro set of patches:

• Start by compiling a new kernel in kvm
• Reboot
• Make sure you loaded the modified kernel module (make reload)
• Go to nitro to setup the userland component and intercept syscalls
• Compile the modified version of qemu if you intend to analyze syscall events

References

Based on Jonas Pfoh's work:

• Nitro: Hardware-based System Call Tracing for Virtual Machines
• Nitro - VMI Extensions for Linux/KVM

Maintainers

@Wenzel

Contributing

PRs accepted.

Small note: If editing the Readme, please conform to the standard-readme specification.

License

GNU General Public License v3.0