Monday, September 24, 2012

Remote kernel debugging using Windbg.

In the following article we will discuss two different methods of remote kernel debugging using Windbg and also various operating systems. Let's begin!

NOTE: It is recommended that you use VMware for this I have NOT tested this on any other virtualisation software.

1. VirtualKD:

Giving the fact that this is a straight forward installation we will not be covering this in depth, you can find information and the download link on the official website at:-

http://virtualkd.sysprogs.org/

Important notes:

- This only works between a HOST and Virtual Machine it will NOT WORK between two virtual machines.
- Very fast debugging compared to Serial Ports.
- Only works on a Windows host so if you with to do this on OS X or Linux this will not help you. (There might be other similar software to help you achieve this however I am not aware of any)

2. Serial Ports:

This method even though it's documented I found that most of the online sources I found were missing different steps or were covering an older version of VMware. For the following example we will use the following names:

"DEBUGEE" - Machine to be debugged.
"DEBUGGER" - Machine which runs the debugger.

Make sure you have Windows Debugging tools installed on the debugger, if you do not you can download and install it at the following url:-

http://msdn.microsoft.com/en-us/windows/hardware/gg463009.aspx

The next step is to edit the .vmx file of both debugger and debugee, before saving the changed make sure you have no serialport0 line before.

WINDOWS:
* DEBUGGER:

serial0.present = "FALSE"
serial1.present = "TRUE"
serial1.fileType = "pipe"
serial1.yieldOnMsrRead = "TRUE"
serial1.startConnected = "TRUE"
serial1.fileName = "\\.\pipe\D:\windbg"
serial1.pipe.endPoint = "client"

* DEBUGEE:

serial0.present = "FALSE"
serial1.present = "TRUE"
serial1.fileType = "pipe"
serial1.yieldOnMsrRead = "TRUE"
serial1.startConnected = "TRUE"
serial1.fileName = "\\.\pipe\D:\windbg"

Of course the fileName should be a valid path.

OS X / LINUX:
* DEBUGGER:

serial0.present = "FALSE"
serial1.present = "TRUE"
serial1.fileType = "pipe"
serial1.yieldOnMsrRead = "TRUE"
serial1.startConnected = "TRUE"
serial1.fileName = "/private/tmp/windbg"
serial1.pipe.endPoint = "client"


* DEBUGEE:

serial0.present = "FALSE"
serial1.present = "TRUE"
serial1.fileType = "pipe"
serial1.yieldOnMsrRead = "TRUE"
serial1.startConnected = "TRUE"
serial1.fileName = "/private/tmp/windbg"

The same thing applies here, fileName should be a valid path.
Now there is only one step left to do and that is to edit the c:\boot.ini on the debugee and add a line as follows:

multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows Server 2003 Debug" /fastdetect /NoExecute=OptIn /debug /debugport=com2 /baudrate=115200

The above method only applies to Windows XP/2003 for further version you can use bcdedit.exe as follows:

bcdedit /debug on
bcdedit /enum (to see if debug mode is on)
bcedit /dbgsettings Serial debugport:<com_port> baudrate:115200


The last thing you need to do is open Windbg on your debugger and go to "File -> Kernel Debugging" (make sure you select com2 on port) and reboot your debugee machine.

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