Saturday, December 25, 2010

Fed up with blue screen error at least you can change color

Seeing a bluescreen that’s not blue is disconcerting, even for me, and based on the reaction of the TechEd audiences, I bet you’ll have fun generating ones of a color you pick and showing them off to your techy friends. I first saw Dan Pearson do this in a crash dump troubleshooting talk he delivered with Dave Solomon a couple of years ago and now close my Case of the Unexplained presentations with a bluescreen of the color the audience choses (you can hear the audience’s response at the end of this recording, for example). Note that the steps I’m gong to share for changing the color of the bluescreen are manual and only survive a boot session, so are suitable for demonstrations, not for general bluescreen customization. Be sure to check out the special holiday bluescreen I’ve prepared for you at the end of the post.

Preparing the System

Because you’re going to modify kernel code, the first step is to enable the ability to edit kernel code in memory if it’s not already enabled. Windows systems with less than 2 GB of RAM uses 4KB pages to store kernel code, so can protect pages with the protection most suitable for the contents they contain. For instance, kernel data pages should allow both read and write access while kernel code should only allow read and execute access. As an optimization that helps improve the speed of virtual address translations, Windows uses large pages (4 MB on x86 and x64) on larger systems. That means that if there’s both code and data stored in a page, the page must allow read, write and execute accesses, so to ensure that you can edit a page, you have to encourage Windows to use large pages. If your system is Windows XP or Server 2003 and has less than 256 MB, or is Windows Vista or higher and has 2 GB or less of RAM, create a REG_DWORD value called LargePageMinimum that’s set to 1 under HKLM\System\CurrentControlSet\Control\Session Manager\Memory Management:


So that you don’t have to rush to show off your handiwork before Windows automatically reboots after the crash, change the auto-reboot setting. On Windows XP and Server 2003, right-click on My Computer, select the Advanced Tab, and press the Settings button in the “Startup and Recovery” section. On Windows Vista and higher, right-click on Computer in the Start Menu, select properties to open the Properties dialog, click Advanced System Settings, select the Advanced tab and press the Settings button in the “Startup and Recovery” section. Finally, uncheck the “Automatically restart” checkbox:


If you’re running 64-bit Windows Vista or higher, you need to boot the system in Debug mode so that you can run the kernel debugger in “local” mode. You can do that either by selecting F8 during the system boot and choosing the Debug boot or by checking the Debug checkbox in the System Configuration (Msconfig) utility:


Next, reboot the system and start the debugger with administrator rights (if UAC is on, run it as administrator). Point the debugger at the Microsoft symbol server by opening the Symbol Search Path dialog under the File menu and enter this string: srv*c:\symbols* (replace c:\symbols with whatever local directory in which you want the debugger to store cached symbols). Next, open the Kernel Debugging dialog from the File menu, click the Local page, and press OK:


The subsequent steps vary depending on whether you’re running 32-bit or 64-bit Windows and whether it’s Windows Vista or newer.

32-bit Windows XP and Windows Server 2003

The function that displays the bluescreen on these operating systems is KeBugCheck2. You’re looking for the place where the function passes the color value to the function that fills the screen background, InbvSolidColorFill. Enter the command “u kebugcheck2” to list the start of the function, then enter the “u” command to dump additional pages of the function’s code until you see the reference to InbvSolidColorFill (after entering “u” once, you can just press enter to repeat the command). You’ll need to dump 30-40 pages before you come across the one with the call:


Preceding the call, you’ll see an instruction that has the number 4 as its argument (“push 4”), as you can see above. Copy the code address of that instruction by selecting it from the address column on the left and typing Ctrl+C. Then in the debugger command window, type “eb “, then Ctrl+V to paste the address, then “+1”, then enter. The debugger will go into memory editing mode, starting with the address of the color value. Now you can choose the color you want. 1 is red, 2 is green, and you can experiment if you want a different color. Simply enter the number and press enter twice to commit it and exit editing mode. Here’s what the screen should look like after you’re done:


64-bit Versions of Windows and 32-bit Windows Vista and Higher

On these versions of Windows, the core bluescreen drawing function is KiDisplayBlueScreen. Type “u kidisplaybluescreen” and then continue entering “u” commands to dump pages of the function until you see the call to InbvSolidColorFill. On 32-bit versions of Windows, continue by following the instructions given in the Windows XP/Server 2003 section to find and edit the color value. On 64-bit versions of these operating systems, the instruction preceding the call to InvbSolidColorFill is the one that passes the color, so copy its address (the number in the left column) and enter this command to edit it: “eb

+4”. The debugger will go into memory editing mode and you can change the value (e.g. 1 for red, 2 for green):


Viewing the Result

You’re now ready to crash the system. If you’re running 64-bit Windows, you might get a crash without doing anything additionally. That’s because Kernel Patch Protection will notice the modification and crash the system as a deterrent to ISVs that might consider modifying the kernel’s code to change its behavior. There might be a delay of up to several minutes before that happens, though. To generate a crash on demand, run the Notmyfault tool (you can download it from the Windows Internals book page) and press the “Do Bug” button (to avoid data loss, make sure you’ve saved any work and closed all other applications):


You’ll now get a bluescreen in the color you picked, in this case the red screen of death:


The Holiday Bluescreen

In the spirit of the holiday season, I took things one step further to generate a holiday-themed bluescreen: not only did I modify the background color, but the text color as well. To do this on 64-bit versions of Windows Vista or higher, note the call to InvbSetTextColor immediately following the one to InvbSolidColorFill and the address of the instruction that passes the text color to the function, “move ecx, 0Fh”:


The 0Fh parameter represents white, but you can change it using the same editing technique. Use the “eb” command, passing the address of the instruction plus 1. Here I set the color to red (which is a value of 1):


And here’s the festive bluescreen I produced:


Happy holidays! And remember, if you have any troubleshooting cases you want to share, please send me screenshots (.PNG preferred) and log files.

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