Wintun Network Adapter

TUN Device Driver for Windows

This is a layer 3 TUN driver for Windows 7, 8, 8.1, and 10. Originally created for WireGuard, it is intended to be useful to a wide variety of projects that require layer 3 tunneling devices with implementations primarily in userspace.

Build Requirements

• Visual Studio 2019
• Windows Driver Kit for Windows 10, version 1903
• WiX Toolset 3.11.1

Digital Signing

Digital signing is integral part of the build process. By default, the driver will be test-signed using a certificate that the WDK should automatically generate. To subsequently load the driver, you will need to put your computer into test mode by executing as Administrator bcdedit /set testsigning on.

If you possess an EV certificate for kernel mode code signing you should switch TUN driver digital signing from test-signing to production-signing by authoring your wintun.vcxproj.user file to look something like this:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <SignMode>ProductionSign</SignMode>
    <CrossCertificateFile>$(WDKContentRoot)CrossCertificates\DigiCert_High_Assurance_EV_Root_CA.crt</CrossCertificateFile>
    <ProductionCertificate>DF98E075A012ED8C86FBCF14854B8F9555CB3D45</ProductionCertificate>
    <TimestampServer>http://timestamp.digicert.com</TimestampServer>
  </PropertyGroup>
</Project>

Modify the <CrossCertificateFile> to contain the full path to the cross-signing certificate of CA that issued your certificate. You should be able to find its .crt file in C:\Program Files (x86)\Windows Kits\10\CrossCertificates. Note that the $(WDKContentRoot) expands to C:\Program Files (x86)\Windows Kits\10\.

If you already have wintun.vcxproj.user file, just add the <PropertyGroup> section.

Building from Command Line

Open Developer Command Prompt for VS 2019 and use the msbuild command:

msbuild wintun.proj [/t:<target>]

Targets

• Build: Builds the driver release configurations of all supported platforms. This is the default target.

• Clean: Deletes all intermediate and output files.

• Rebuild: Alias for Clean followed by Build.

• SDV: Runs Static Driver Verifier, which includes a clean driver build, only for AMD64 release configuration.

• DVL: Runs the SDV, and creates a Driver Verification Log, only for AMD64 release configurations.

• MSM: Builds Microsoft Installer Merge Modules in <output folder>\wintun-<platform>-<version>.msm. Requires WHQL signed driver.

The driver output folders are:

Do note that since the Build target builds for all supported platforms, you will need to have the toolchains installed for those platforms.

Building Microsoft Installer Merge Modules

1. msbuild wintun.proj /t:DVL;Build.
2. Perform Windows Hardware Lab Kit tests.
3. Submit submission package to Microsoft.
4. Copy WHQL-signed driver to x86\Release\whql\ and amd64\Release\whql\ subfolders.
5. msbuild wintun.proj /t:MSM
6. MSM files are placed in dist subfolder.

Note: due to the use of SHA256 signatures throughout, Windows 7 users who would like a prompt-less installation generally need to have the KB2921916 hotfix installed, which can be obtained from these mirrors: amd64 and x86.

Usage

After loading the driver and creating a network interface the typical way using SetupAPI, open \\.\Device\WINTUN%d as Local System, where %d is the LUID index (NetLuidIndex member) of the network device. You may then ReadFile and WriteFile bundles of packets of the following format:

+------------------------------+
| size_0                       |
|   4 bytes, native endian     |
+------------------------------+
|                              |
| packet_0                     |
|   size_0 bytes               |
|                              |
~                              ~
|                              |
+------------------------------+
| padding                      |
|   4-(size_0&3) bytes         |
+------------------------------+
| size_1                       |
|   4 bytes, native endian     |
+------------------------------+
|                              |
| packet_1                     |
|   size_1 bytes               |
|                              |
~                              ~
|                              |
+------------------------------+
| padding                      |
|   4-(size_1&3) bytes         |
+------------------------------+
~                              ~

Each packet segment should contain a layer 3 IPv4 or IPv6 packet. Up to 15728640 bytes may be read or written during each call to ReadFile or WriteFile. All calls to ReadFile must be called with the same virtual address, for a given handle. This virtual address must reference pages that are writable for the same length as passed to the first call of ReadFile.

It is advisable to use overlapped I/O for this. If using blocking I/O instead, it may be desirable to open separate handles for reading and writing.