shv.c

/*++

Copyright (c) Alex Ionescu.  All rights reserved.

Module Name:

    shv.c

Abstract:

    This module implements the Driver Entry/Unload for the Simple Hyper Visor.

Author:

    Alex Ionescu (@aionescu) 16-Mar-2016 - Initial version

Environment:

    Kernel mode only.

--*/

#include "shv.h"

PSHV_GLOBAL_DATA ShvGlobalData;

VOID
ShvUnload (
    _In_ PDRIVER_OBJECT DriverObject
    )
{
    UNREFERENCED_PARAMETER(DriverObject);

    //
    // Attempt to exit VMX root mode on all logical processors. This will
    // broadcast a DPC interrupt which will execute the callback routine in
    // parallel on the LPs. Send the callback routine a NULL context in order
    // to indicate that this is the unload, not load, path.
    //
    // Note that if SHV is not loaded on any of the LPs, this routine will not
    // perform any work, but will not fail in any way.
    //
    KeGenericCallDpc(ShvVpCallbackDpc, NULL);

    //
    // If the SHV was not fully/correctly loaded, we may not have global data
    // allocated yet. Check for that before freeing it.
    //
    // Note that KeGenericCallDpc is guaranteed to return only after all LPs
    // have succesfully executed the DPC and synchronized. This means that SHV
    // is fully unloaded, and no further VMEXITs can return. It is safe to free
    // this data.
    //
    if (ShvGlobalData != NULL)
    {
        MmFreeContiguousMemory(ShvGlobalData);
    }

    //
    // Indicate unload
    //
    DbgPrintEx(77, 0, "The SHV has been uninstalled.\n");
}

NTSTATUS
ShvInitialize (
    _In_ PDRIVER_OBJECT DriverObject,
    _In_ PUNICODE_STRING RegistryPath
    )
{
    UNREFERENCED_PARAMETER(RegistryPath);

    //
    // Detect if a hypervisor is already loaded, using the standard high bit in
    // the ECX features register. Hypervisors may choose to hide from this, at
    // which point entering VMX root mode will fail (unless a shadows VMCS is
    // used).
    //
    if (HviIsAnyHypervisorPresent())
    {
        return STATUS_HV_OBJECT_IN_USE;
    }

    //
    // Next, detect if the hardware appears to support VMX root mode to start.
    // No attempts are made to enable this if it is lacking or disabled.
    //
    if (!ShvVmxProbe())
    {
        return STATUS_HV_FEATURE_UNAVAILABLE;
    }

    //
    // Allocate the global shared data which all virtual processors will share.
    //
    ShvGlobalData = ShvVpAllocateGlobalData();
    if (!ShvGlobalData)
    {
        return STATUS_HV_INSUFFICIENT_BUFFER;
    }

    //
    // Attempt to enter VMX root mode on all logical processors. This will
    // broadcast a DPC interrupt which will execute the callback routine in
    // parallel on the LPs. Send the callback routine the physical address of
    // the PML4 of the system process, which is what this driver entrypoint
    // should be executing in.
    //
    NT_ASSERT(PsGetCurrentProcess() == PsInitialSystemProcess);
    KeGenericCallDpc(ShvVpCallbackDpc, (PVOID)__readcr3());

    //
    // A hypervisor should now be seen as present on this (and all other) LP,
    // as the SHV correctly handles CPUID ECX features register.
    //
    if (HviIsAnyHypervisorPresent() == FALSE)
    {
        MmFreeContiguousMemory(ShvGlobalData);
        return STATUS_HV_NOT_PRESENT;
    }

    //
    // Make the driver (and SHV itself) unloadable, and indicate success.
    //
    DriverObject->DriverUnload = ShvUnload;
    DbgPrintEx(77, 0, "The SHV has been installed.\n");
    return STATUS_SUCCESS;
}