74  WinDBG Kernel-mode Debugging (KD)

The WinDBG KD interface support for rizin allows you to attach to VM running Windows and debug its kernel over a serial port or network.

It is also possible to use the remote GDB interface to connect and debug Windows kernels without depending on Windows capabilities.

Bear in mind that WinDBG KD support is still work-in-progress, and this is just an initial implementation which will get better in time.

74.1 Setting Up KD on Windows

For a complete walkthrough, refer to Microsoft’s documentation.

74.1.1 Serial Port

Enable KD over a serial port on Windows Vista and higher like this:

bcdedit /debug on
bcdedit /dbgsettings serial debugport:1 baudrate:115200

Or like this for Windows XP: Open boot.ini and add /debug /debugport=COM1 /baudrate=115200:

[boot loader]
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Debugging with Cable" /fastdetect /debug /debugport=COM1 /baudrate=57600

In case of VMWare

    Virtual Machine Settings -> Add -> Serial Port
    Device Status:
    [v] Connect at power on
    [v] Use socket (named pipe)
    From: Server To: Virtual Machine

Configure the VirtualBox Machine like this:

    Preferences -> Serial Ports -> Port 1

    [v] Enable Serial Port
    Port Number: [_COM1_______[v]]
    Port Mode:   [_Host_Pipe__[v]]
                 [v] Create Pipe
    Port/File Path: [_/tmp/winkd.pipe____]

Or just spawn the VM with qemu like this:

$ qemu-system-x86_64 -chardev socket,id=serial0,\
     path=/tmp/winkd.pipe,nowait,server \
     -serial chardev:serial0 -hda Windows7-VM.vdi

74.1.2 Network

Enable KD over network (KDNet) on Windows 7 or later likes this:

bcdedit /debug on
bcdedit /dbgsettings net hostip:w.x.y.z port:n

Starting from Windows 8 there is no way to enforce debugging for every boot, but it is possible to always show the advanced boot options, which allows to enable kernel debugging:

bcedit /set {globalsettings} advancedoptions true

74.2 Connecting to KD interface on rizin

74.2.1 Serial Port

Rizin will use the winkd io plugin to connect to a socket file created by virtualbox or qemu. Also, the winkd debugger plugin and we should specify the x86-32 too. (32 and 64 bit debugging is supported)

$ rizin -a x86 -b 32 -D winkd winkd:///tmp/winkd.pipe

On Windows you should run the following line:

$ rizin -D winkd winkd://\\.\pipe\com_1

74.2.2 Network

$ rizin -a x86 -b 32 -d winkd://<hostip>:<port>:w.x.y.z

74.3 Using KD

When connecting to a KD interface, rizin will send a breakin packet to interrupt the target and we will get stuck here:

[0x828997b8]> pd 20
    ;-- eip:
    0x828997b8    cc           int3
    0x828997b9    c20400       ret 4
    0x828997bc    cc           int3
    0x828997bd    90           nop
    0x828997be    c3           ret
    0x828997bf    90           nop

In order to skip that trap we will need to change eip and run ‘dc’ twice:

dr eip=eip+1
dr eip=eip+1

Now the Windows VM will be interactive again. We will need to kill rizin and attach again to get back to control the kernel.

In addition, the dp command can be used to list all processes, and dpa or dp= to attach to the process. This will display the base address of the process in the physical memory layout.

75 WinDBG Backend for Windows (DbgEng)

On Windows, rizin can use DbgEng.dll as a debugging backend, allowing it to make use of WinDBG’s capabilities, supporting dump files, local and remote user and kernel mode debugging.

You can use the debugging DLLs included on Windows or get the latest version from Microsoft’s download page (recommended).

You cannot use DLLs from the Microsoft Store’s WinDbg Preview app folder directly as they are not marked as executable for normal users.

rizin will try to load dbgeng.dll from the _NT_DEBUGGER_EXTENSION_PATH environment variable before using Windows’ default library search path.

75.1 Using the plugin

To use the windbg plugin, pass the same command-line options as you would for WinDBG or kd (see Microsoft’s documentation), quoting/escaping when necessary:

> rizin -d "windbg://-remote tcp:server=Server,port=Socket"
> rizin -d "windbg://MyProgram.exe \"my arg\""
> rizin -d "windbg://-k net:port=<n>,key=<MyKey>"
> rizin -d "windbg://-z MyDumpFile.dmp"

You can then debug normally (see d? command) or interact with the backend shell directly with the R! command:

[0x7ffcac9fcea0]> dcu 0x0007ffc98f42190
Continue until 0x7ffc98f42190 using 1 bpsize
ModLoad: 00007ffc`ab6b0000 00007ffc`ab6e0000   C:\WINDOWS\System32\IMM32.DLL
Breakpoint 1 hit
hit breakpoint at: 0x7ffc98f42190

[0x7fffcf232190]> R!k4
Child-SP          RetAddr           Call Site
00000033`73b1f618 00007ff6`c67a861d r_main!r_main_rizin
00000033`73b1f620 00007ff6`c67d0019 rizin!main+0x8d
00000033`73b1f720 00007ff6`c67cfebe rizin!invoke_main+0x39
00000033`73b1f770 00007ff6`c67cfd7e rizin!__scrt_common_main_seh+0x12e