Friday, 16 December 2016
Look What I did!
Look What I did!
Finally got my computer to boot to an EFI file! Took me about 4 months, and it ended up being really simple. Wasted a lot of time modifying and flashing my BIOS to go about it different ways, and finally one of my ideas worked. This is on my HP dv7t-4100, which is a laptop with almost all of its EFI functionality hidden or removed by its manufacture. Took advantage of HPs System Diagnostics UEFI Tool since I knew that this is the only case when my computer would natively boot to an EFI file.
The file HPs tool runs is CryptRSA.efi which verifies the signature of SystemDiags.efi before preceding to pass control to that file. Unfortunately modifying any of these files would prevent booting into the diagnostics tool. I looked through a bunch of CryptRSA.efi files from a lot of different versions of HPs applications and noticed that they were all exactly the same. This made me assume that they didnt modify them because all their BIOS already implemented the code to verify that specific CryptRSA.efi files integrity. So they would have to release updates for all BIOS if they were to alter CryptRSA.efi in any way.
So then it was just down to finding out how they verified that file and how I could modify this verification to launch a different EFI file. Easy enough since their CryptRSA.efi verification was just a SHA-1 hash. In the end Im now capable of booting into an EFI shell!
And heres me trying to run Windows 8s installer on my MBR disk. I guess its time to switch over to GPT.
Update: Crahzee successfully performed the same mod on his HP G62-220CA bios. Congratulations! Hes the first person Ive seen recreate this! Heres a screen shot of his work. Hope Crahzee doesnt mind me posting this. I like it a lot because it says my name a few times lol :)
Available link for download
