hv

hv is an x86-64 Intel VT-x hypervisor that aims to be simple and lightweight, while still following the Intel SDM as closely as possible. This allows it to evade detections that take advantage of common hypervisor bugs, such as improper vm-exit handling. Other detections, such as timing checks, are mostly mitigated, although staying fully undetected is nearly impossible.

Installation

To clone the repo:

git clone --recursive https://github.com/jonomango/hv.git

hv is a Windows driver built with MSVC. It requires Visual Studio and the WDK for compilation.

Once compiled, simply load hv.sys anyway you'd like (either by using the Windows Service Control Manager or a manual mapper) and it will immediately virtualize the system. To check if hv is currently running, try to execute the ping hypercall and see if it responds appropriately. Unloading the driver will result in hv::stop() being called, which will devirtualize the system.

Hypercalls

hv has a full hypercall interface that can be used from both ring-0 and ring-3. It relies on the VMCALL instruction and has a particular calling convention that must be followed. Check out hv/vmx.asm for how this can be implemented.

Additionally, hypercalls will not function correctly unless provided with the correct hypercall_key. This can be easily modified in the source code and is used to ensure that malicious guests cannot execute any hypercalls.

Example of executing the ping hypercall:

// setup the hypercall input
hv::hypercall_input input;
input.code = hv::hypercall_ping;
input.key  = hv::hypercall_key;

// execute the hypercall
auto const value = hv::vmx_vmcall(input);

if (value == hv::hypervisor_signature)
  printf("pong!\n");

Adding New Hypercalls

Extending the hypercall interface is pretty simple. Add your new hypercall handler to hv/hypercalls.h and hv/hypercalls.cpp, then modify emulate_vmcall() to call your added code.