Related link: http://www.hackaday.com/entry/1234000687060851/
I mentioned this on my blog for the book yesterday, but yesterday morning, my step-by-step walk through of the PSP firmware 2.0 to 1.5 downgrade process appeared on hackaday, and then later in the day was mentioned on G4's Attack of the Show. I missed the show, but heard about it from friends later. If anyone has a screen grab of the mention, let me know. Even if I don't ever track one down, it's still pretty cool.
However, the coolest thing about all this is the downgrade exploit itself, so I thought I would follow up on my how-to with a short discussion here of how (it seems) to work.
A tiff file is placed in the /PSP/PHOTO/ folder on the Memory Stick, which when accessed via the PSP's interface causes a buffer overflow, whereby a bit of code is executed that changes the system info of the PSP. On restart, the PSP is fooled into thinking that it is running version 1.0 of the firmware. It isn't. It still is running 2.0, but when you go to System Information pane on your PSP it will say it is running 1.0. More importantly, when you try to run the 1.5 Firmware Update, the program that checks to make sure that you need the update also is fooled by this simple substitution of 1.0 for 2.0. It suddenly thinks "Oh this is a 1.0 PSP so I should allow this updater to run." The updater then runs and errors out and freezes at 99%. Force the PSP to restart by holding the power for a little over 10 seconds and when it boots back up you're suddenly running 1.5 and the whole wide world of homebrew is open to you. Now for the bit of warning: this is a firmware operation, so keep in mind that as with any firmware update, a loss of power during installation could turn your PSP swiftly into a very attractively designed doorstop.
I wonder how long before Sony comes out with firmware 2.01 and tries to throw another roadblock in the way. I'm more optimistic about everything they throw in the path of homebrew eventually being overrun by the great group of hackers out there chipping diligently away at the code to keep things open.
Do you do PSP homebrew? If so, what are your favorite bits and pieces? I like PSPChess, myself...
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