We need Intel System Studio installed on our host machine. If we check the USB Tree View, the Target should appear like this: Next we plug in our target machine to our host machine using a USB3.0 cross over cable. Make all of the aforementioned offset changes, write the values to BIOS, and then exit the application and run reset at the UEFI shell. To write the value back to BIOS, press crtl+ w. We now use RU.EFI’s hex editor to modify bytes in the Setup variable:Ĭhanges are made by using the arrow keys to select the appropriate offset and then entering the hex value and pressing enter. The relevant output is posted below:Ġx24972 QuestionId: 0xC85 equals value 0x0 įrom this we can come up with a list of Setup variable offsets that need to be changed: We are looking specifically for UEFI Variables related to DCI or Debugging. This tool leaves us with a lot of output we need to sort through. Universal IFR Extractor can be downloaded here. Next we run the Universal IFR Extractor tool on the extracted setup file. Once I had the BIOS as a binary file, I used UEFITool to extract the Setup UEFI Variable: Uefitool add uefi shell to bios driver#Chipsec will run on Windows as well, although buidling the kernel driver is a manual process under Windows. The chipsec command is chipsec_util spi dump $OUT_FILE_NAME. I did this using Chipsec using Linux as the operating system on the target. The first step is to dump the system bios from the target machine. We will mostly be working with the UEFI Variables Menu, which can be accessed via alt+ =. It can be called at any time with alt+ qĮach menu can be accessed via pressing alt and the underline character key. There are seven menus available from the top menu bar:Īnd then the last menu, Quit simply exits the application. Once you have done that, you will be shown the initial application welcome message:Īfter dismissing the welcom screen you will be presented with the application. The commands look like this when RU.EFI is in /efi: Then if you boot off that same USB drive, you should see the EFI shell. You could even put ru.efi in /efi/boot/boot圆4.efi and boot directly into the RU.EFI application, if you so desired. I usually put it in EFI, but it does not matter where it is as long as its on the usb drive. You can then copy RU.EFI onto the USB drive. You can find a copy of the EFI shell in the chipsec repo here. Then create the directory structure /efi/boot/ and copy the UEFI shell binary into the boot directory naming it boot圆4.efi. I found the easiest way to boot into an EFI shell is to use a USB stick formatted as FAT. You will need to launch RU.EFI from a UEFI Shell. Uefitool add uefi shell to bios code#I haven’t observed any suspicious behavior, but without having the source code it is very difficult to know if there is any such behavior built in. Since RU.EFI is not open source, I don’t recommend running it on a production machine or a machine with “live” data if you will. Uefitool add uefi shell to bios zip file#Note that the zip file is encrypted with a password that can only be found in the aforementioned blogpost link. The latest version as of this writing can be found here. RU.EFI is an UEFI Application that can assist in the examination and modification of System BIOS on a running machine. However, this post will focus on using RU.EFI to modify UEFI Variables in BIOS as this is a topic that is not covered in depth in prior art. I will go through the steps of enabling DCI on a GPD Pocket 2 and show a system halt on the host machine of the target CPU. These two articles outline the process of enabling DCI. There is significant prior art in this area which I would like to credit: DCI is Intel’s Ring -2 debugging tool which enables a host to debug the BIOS and operating system of a target machine via a USB cable. The objective is to enable Intel DCI on a GDP Pocket 2. Uefitool add uefi shell to bios how to#This post will describe how to use RU.EFI to modify UEFI Variables in system BIOS. Project maintained by nstarke Hosted on GitHub Pages - Theme by mattgraham 01 August 2020 Modifying BIOS Using RU.EFI
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