S5L8900

This is the Application Processor shared between the iPhone, iPod touch, and the iPhone 3G. Not much is known about it through official sources. This processor is not used in any of the newest devices, being replaced by the S5L8720 and S5L8920.

Exploits

Userland

• Restore Mode - Firmware v1.0.2 and below
• Symlinks - Firmware v1.1.1 and below
• LibTIFF - Firmware v1.1.1 and below
• Mknod - Firmware v1.1.2 and below
• Dual Boot Exploit - Firmware 1.1.4 / v2.0b3 and below

iBoot / Kernel

• Ramdisk Hack - Firmware v1.1.4 / v2.0b3 and below
• Diags Exploit - Firmware v1.1.4 / v2.0b5 and below
• iBoot Environment Variable Overflow - Firmware 3.1b1 and below

Bootrom

• Pwnage 1.0 (Ramdisk + AppleImage2NORAccess)
• Pwnage 2.0 (DFU + Malformed Certificate)

Boot Chain

VROM->LLB->iBoot->Kernel->System Software

One of the iPhoneLinux goals are to replace that Boot Chain after iBoot:
VROM->OpeniBoot->Linux Kernel->X Server->Window Manager

Upgrade Process

Restore Mode

The common upgrade process chain is VROM->DFU->WTF->iBoot->Kernel->Ramdisk->Restore Mode.

DFU Mode

To flash an older version of the iPhone software you have to let your phone reside in DFU. In iTunes you have to press the option key (Mac) or the shift key (Windows) when pressing 'Restore' to be able to manually chose an IPSW.

Boot Chain

VROM->DFU