win-pxe-boot

Reference for making Windows (10) boot from network/PXE i.e. inside KVM/QEMU

The purpose of this collection of script is to capture the process of network booting the Windows in particular WinPE. Tested on Windows 10 (19H2), but should work on any Windows10+ eventually also for older versions but that might need some tweaks.

Quick start:

• tftp/simple.ipxe - to switch from TFTP to HTTP
• web/next.ipxe - the next stage loaded over HTTP
• web/wimboot - the magic wimboot (bootloader, download at: https://github.com/ipxe/wimboot/releases)
• web/boot/bcd - the boot config (registry hive, get from WinPE ISO)
• web/boot/bcd.sdi - the ramdisk (X: drive, get from WinPE ISO)
• web/sources/winpe.wim - the actuall Windows PE (expanded into X:, get from WinPE ISO)

Section on making WinPE ISO.

The just start the:

0. make the network switch for testing brhost
1. dnsmasq (host) - DHCP + DNS + TFTP server, listen on brhost IP
2. nginx web server (dockerized) - HTTP SERVER, listen on brhost IP
3. kvm/qemu to test (see example at the end of this file)

OpenVSwitch brhost

Transient network:

BRN=brhost
OIF=eth0
# make device
ovs-vsctl add-br $BRN
# set device up
ip link set dev $BRN up
# set ip
ip address add 192.168.100.1/24 dev $BRN
# Optional: configure forwarding and SNAT
iptables -I FORWARD -i $BRN -o $OI -j ACCEPT
iptables -I FORWARD -o $BRN -i $OI -j ACCEPT
iptables -t nat -I POSTROUTING -o $OIF -j MASQUERADE
# you might need to change '-I' to '-A' eventually
# in case you have bridge traffic filtered in some way
# /etc/sysctl.d/50-no-bridge-iptables.conf
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
# sysctl -p /etc/sysctl.d/50-no-bridge-iptables.conf
# to turn that filtering off completely - just for testing
# in other cases you might need to tweak the rules in a way
# that it let through the legitimate traffic
# this might become complex :-) with IPv4/6 and ARP

Slow start

Principal steps:

1. Get winpe.wim more, boot.wim or install.wim from install ISO/CDROM @ \sources\boot.wim or \sources\install.wim
2. Configure and run DHCP and HTTP servers (good tip is to use dnsmasq, nginx and optionally php-fpm)
3. Test everything with KVM/QEMU (boot>network)
4. Use on your network as needed

Microsoft on boot process

Note: The WinPE is a base Windows Image, that can turn into install, WinRE or other purpose short-lived instance of windows, with limited capabilities (i.e. w/o USERs, extra SW). There is a option to customize the bare image using winpeshl.ini an example and/or startnet.cmd

You might find useful to manipulate the *.wim images using dism

The magic is done by wimboot for technical internals check the ipxe.org/wimboot web.

Define virtual machine to test things

The way to build the virsh image can be following:

#!/bin/bash

set -x
set -e

VM_NAME=wimtest
VM_CPU=1
VM_NET_NAME=brhost
VM_NIC_MAC=52:54:00:00:00:01
VM_RAM=2048

virt-install \
    --dry-run \
    --import \
    --print-xml \
    --name=${VM_NAME} \
    --arch=x86_64 \
    --vcpus=${VM_CPU} \
    --cpu=host \
    --os-type=windows \
    --os-variant=win10 \
    --network bridge=${VM_NET_NAME},mac=${VM_NIC_MAC},model=virtio \
    --graphics vnc,listen=127.0.0.1,port=5900 \
    --hvm \
    --video model=virtio,model.vram=16384 \
    --ram=${VM_RAM} \
    --boot network \
| tee vm.xml

That yields file similar to vm.xml.

You might find useful to add the target disk image for installation or floppy with drivers or iso with drivers. Eventually the second ISO with install files if not using the SMB share. You can also benefit from WinPE to dism /Image-Apply a wim file to the target disk. It is fast and convenient. Please do not forget to fix, update the MBR, partition bootsect or EFI partition as needed to make the disk bootable.

Getting into PXE

The network booting can be complicated. There are at least two boot environments the BIOS and UEFI. Not taking into account the CoreBoot (former LinuxBoot). The initial test environment was BIOS based KVM virtual machine.

The common issue is also gathering the correct files based on your PXE environment. It migh be pxelinux.0, undi.kpxe, boot32.efi, boot64.efi. Also the subsequent stage wimboot requires few files from windows install ISO like bcd, bcd.sdi. Some other files are used directly from the WIM file.