ionescu007/simplevisorMinimal Intel VT-x hypervisor for Windows and UEFI that virtualizes a live host for introspection, supporting dynamic hyperjacking, unhyperjacking, EPT, and VPID.
SimpleVisor is a simple, portable, Intel x64/EM64T VT-x specific hypervisor with two specific goals: using the least amount of assembly code (10 lines), and having the smallest amount of VMX-related code to support dynamic hyperjacking and unhyperjacking (that is, virtualizing the host state from within the host) while also supporting advanced features such as EPT and VPID. It currently runs on both Windows and in UEFI environments.
Have you always been curious on how to build a hypervisor? Has Intel's documentation (the many hundreds of pages) gotten you down? Have the samples you've found online just made things more confusing, or required weeks of reading through dozens of thousands of lines and code? If so, SimpleVisor might be the project for you.
Not counting the exhaustive comments which explain every single line of code, and specific Windows-related or Intel-related idiosyncrasies, SimpleVisor clocks in at about 500 lines of C code, and 10 lines of x64 assembly code, all while containing the ability to run on every recent version of 64-bit Windows, and supporting dynamic load/unload at runtime.
Additionally, SimpleVisor utilizes a lightweight OS-library for Windows-specific functionality, separating out the hypervisor pieces from the Windows-specific pieces. Leveraging this portable design, a UEFI version of SimpleVisor is also now available. Note however, that it does not have robust support for MP environments due to issues with UEFI, and that loading an operating system will eventually result in a crash as the OS will hit unimplemented code paths due to its re-configuration of processor resources. Virtualizing the entire boot of the operating system from UEFI is beyond the scope of the project.
SimpleVisor can be built with Visual Studio 2015 Update 3, and while older/newer compilers have not been tested and are not supported, it's likely that they can build the project as well. It's important, however, to keep the various compiler and linker settings as you see them, however.
SimpleVisor has currently been tested on the following platforms successfully:
At this time, it has not been tested on Bochs, but there's no reason why SimpleVisor could not run in such an environment as well. However, if your machine is already running under a hypervisor such as Hyper-V or Xen, SimpleVisor will not load.
Keep in mind that x86 versions of Windows are expressly not supported, nor are processors earlier than the Nehalem microarchitecture, nor is Windows 7. Support for the latter two is easy to add and exists in certain forks.
Too many hypervisor projects out there are either extremely complicated ([Xen][1], KVM, VirtualBox) and/or closed-source (VMware, Hyper-V), as well as heavily focused toward Linux-based development or system. Additionally, most (other than Hyper-V) of them are expressly built for the purpose of enabling the execution of virtual machines, and not the virtualization of a live, running system, in order to perform introspection or other security-related tasks on it.
A few projects do stand out from the fold however, such as the original [Blue Pill][2] from Joanna, or projects such as [VirtDbg][3] and [HyperDbg][4]. Unfortunately, most of these have become quite old by now, and some only function on x86 processors, and don't support newer operating systems such as Windows 10. Another rather simple example, similar to Blue Pill in some aspects, but actually delivering a good example of EPT use for "Split-TLB" is [MoRE][7] from Jacob Torrey/AIS.
The closest project that actually delivers a Windows-centric, modern, and supported hypervisor is [HyperPlatform][5], and we strongly recommend its use as a starting place for more broadly usable research-type hypervisor development. However, in attempting to create a generic "platform" that is more broadly robust, HyperPlatform also suffers from a bit of bloat, making it harder to understand what truly are the basic needs of a hypervisor, and how to initialize one. In a similar vein, and showing an equal love for STL/C++, but also including an ELF loader and UEFI/Linux support alongside unit tests and even more robustness is [Bareflank][8], also from AIS. Beyond that, you're probably getting into Xen-level complexity.
The express goal of this project, as stated above, was to minimize code in any way possible, without causing negative side-effects, and focusing on the 'bare-metal' needs. This includes:
Another implied goal was to support the very latest in hardware features, as even [Bochs][6] doesn't always have the very-latest Intel VMX instructions and/or definitions. These are often found in header files such as "vmcs.h" and "vmx.h" that various projects have at various levels of definition. For example, Xen master has some unreleased VM Exit reasons, but not certain released ones, which Bochs does have, albeit it doesn't have the unreleased ones! One such example is the usage of 1GB EPT entries, which for example VMWare does not virtualize correctly.
Finally, SimpleVisor is meant to be an educational tool -- it has exhaustive comments explaining all logic behind each line of code, and specific Windows or Intel VMX tips and tricks that allow it to achieve its desired outcome. Various bugs or poorly documented behaviors are called out explicitly.
Because x64 Windows requires all drivers to be signed, you must testsign the SimpleVisor binary. The Visual Studio project file can be setup to do so by using the "Driver Signing" options and enabling "Test Sign" with your own certificate. From the UI, you can also generate your own.
