WSL Nested Virtualization

README.md

DISCLAIMER: This can corrupt your WSL or whatever, so no guarantees this works and does what your want. Use at your own risk. Update 02/2023: Added wsl --shutdown in script. Known to work on Intel (AMD likely needs Win11) 21H2 19044.2486

Prereqs:

• Install WinDbg (Preview from the store)

1. You might have to build a custom WSL kernel with KVM support. This seems to be unnecessary with If your kernel is >=v4.19.104.

touch .scmversion
make menuconfig KCONFIG_CONFIG=Microsoft/config-wsl
# Virtualization -> KVM & Intel KVM
# Processor type Features -> /dev/cpu/* /msr support
make -j8 KCONFIG_CONFIG=Microsoft/config-wsl

2. Run start-wsl.bat. If you use a custom kernel, edit it in your wsl config or uncomment the LinuxKernelDirect line in script.js. Thanks to @offlinehacker, who increased automatization of this part!
3. In WSL run sudo kvm-ok and be happy.

run-wsl.bat

REM Ensure vmcompute.exe is running
wsl.exe -e true
REM Listen for and Intercept utility vm creation
start Windbgx.exe -pn vmcompute.exe -c "bp vmcompute!Marshal::JsonParser::JsonParser;g;.scriptrun %CD%\script.js;.scriptrun %CD%\script.js;.scriptrun %CD%\script.js;.detach;qq"
REM Ensure WSL Utility VM is not running (hopefully windb starts up fast enough...)
net stop LxssManager
net start LxssManager
rem might be needed for newer builds
wsl --shutdown
echo "Press Enter if the debugger is running"
pause
REM Start WSL
start wsl.exe

script.js

"use strict";

function initializeScript()
{
    return [new host.apiVersionSupport(1, 3)];
}

function continueExecution() {
    var cmd = "g";
    host.diagnostics.debugLog(cmd);
    var lines = host.namespace.Debugger.Utility.Control.ExecuteCommand(cmd)
    for (var line of lines) host.diagnostics.debugLog("  ", line, "\n");
}

function invokeScript()
{
    /* bp vmcompute!Marshal::JsonParser::JsonParser */

    var cmd;
    var lines;

    // 1. Check if WSL
    var magic = host.memory.readWideString(host.currentThread.Registers.User.rdx, 14);
    if (magic == '{"Owner":"WSL"') {
        host.diagnostics.debugLog("IS WSL\n");
    } else {
        host.diagnostics.debugLog("IS NOT WSL request\n");
        return continueExecution();
    }

    // dump length and read machine spec json
    var len = host.currentThread.Registers.User.r8;
    host.diagnostics.debugLog("String length: ", len, " dumping memory: ", host.currentThread.Registers.User.rdx, "\n");
    var jsonString = host.memory.readWideString(host.currentThread.Registers.User.rdx, len);
    host.diagnostics.debugLog("Before: ", jsonString, "\n");

    // parse and modify machine spec json
    var machineSpec = JSON.parse(jsonString);
    machineSpec.VirtualMachine.ComputeTopology.Processor.ExposeVirtualizationExtensions = true;
    // machineSpec.VirtualMachine.Chipset.LinuxKernelDirect.KernelFilePath = "D:\\temp\\vmlinux.bin";

    var machineSpecJson = JSON.stringify(machineSpec);
    host.diagnostics.debugLog("After:  ", JSON.stringify(machineSpec), "\n");
    var newLen = "0x" + machineSpecJson.length.toString(16);

    // allocate memory
    cmd = ".dvalloc 4096"
    lines = host.namespace.Debugger.Utility.Control.ExecuteCommand(cmd)
    var addr = lines[0];
    var addrParts = addr.split(" ");
    var freeMem = addrParts[addrParts.length-1].replace("`", "");
    host.diagnostics.debugLog("Allocated ", freeMem, "\n");
    
    // write memory
    host.diagnostics.debugLog("Writing memory ", freeMem, " length: ", newLen, "\n");
    cmd = "eu " + freeMem + ' "' + machineSpecJson.split("\\").join("\\\\").split('"').join('\\"') + '"';
    lines = host.namespace.Debugger.Utility.Control.ExecuteCommand(cmd)
    for (var line of lines) host.diagnostics.debugLog("  ", line, "\n");

    // patch rdx with new memory address
    var cmd = "r @rdx = " + freeMem;
    host.diagnostics.debugLog(cmd);
    var lines = host.namespace.Debugger.Utility.Control.ExecuteCommand(cmd)
    for (var line of lines) host.diagnostics.debugLog("  ", line, "\n");

    // patch r8 with new memory size
    var cmd = "r @r8 = " + newLen;
    host.diagnostics.debugLog(cmd);
    var lines = host.namespace.Debugger.Utility.Control.ExecuteCommand(cmd)
    for (var line of lines) host.diagnostics.debugLog("  ", line, "\n");

    return continueExecution();
}

this crash my windows

For anyone failed with prompt like

虚拟机监控程序无法执行此操作，因为指定的参数无效。 // Listerally translates to "hypervisor cannot execute this operation due to invalid arguments
Error code: Wsl/Service/CreateInstance/CreateVm/0xc0350005

Your WSL2 version may to too new to use this hack. To validate, run wsl --version, if you see some versioning info rather than help text, then read on.

You should downgrade WSL2 to some ancient version by:

$pkg = Get-AppxPackage MicrosoftCorporationII.WindowsSubsystemforLinux -AllUsers
Remove-AppxPackage $pkg -AllUsers

Then rerun wsl --version, if help text appears, then congrats, you are good to use this hack.

plus my system is home edition

wsl --version

nice

WSL2 version： 2.0.4.0

i run the script，but not work

any plan to support ？

But i can get it work for ancient version of WSL2 as @ZeppLu mentioned