GeoHot Explains How the PurpleRa1n Jailbreak Works

GeoHot has added an entry to TheiPhoneWiki explaining how his purplera1n iPhone 3GS jailbreak works.

Below you can read the step by step description of what the exploit does...

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* purplera1n sends the enter recovery commands using iTunesMobileDevice
* once in recovery(iBoot), it sends the IBoot Environment Variable Overflow exploit
* the exploit adds a "geohot" command to the phone which runs the payload
* the "geohot" command is run, control is now transferred from iboot to the payload
* the purplera1n client is done


Inside payload
* the payload restores the default environment variable ring buffer and saves the environment to nvram(sets auto-boot to true)
* it patches iBoot to load unsigned img3s and not care about the tags
* it loads the purplera1n picture(sent with payload)
* the nor patcher starts
* llb is decrypted, patched, and increased in size to 0x24200. this is the resident 0x24000 Segment Overflow exploit
* a little loader code is put @ 0x20000 in the LLB to load it and fix the stack
* iboot is decrypted, patched
* everything else is read as is
* nor is written back, nor patcher is done
* kernel is loaded, decrypted, and patched
* ramdisk is loaded(sent with payload) and moved to ramdisk region at 0x44000000, patched kernel is tacked on to the end
* patched kernel is booted
* control is now transferred from payload to ramdisk

Inside ramdisk
* launchd is run, all stuff happens here
* /dev/disk0s1 is mounted
* fstab and services are overwritten here to allow disk0s1 writes and afc2 respectively
* Freeze.app is transferred and Freeze.app loader has SUID bit set
* patched kernel is read from end of ramdisk block device and written to filesystem
* ramdisk is done, rebooting...

Reboots as jailbroken phone
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