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iBoot (Bootloader)
This is Apple's stage 2 bootloader for all of the iDevices. It runs what is known as Recovery Mode. It has an interactive interface which can be used over USB or serial.
Contents
Bootrom
The bootrom also goes by the name "iBoot." The list of bootroms can be found on their own page.
Extract and Disassemble
To extract the bootloader and disassemble using IDA, follow the following steps:
- obtain the bootloader from the iPSW. This file is in the
Firmware/all_flashsubdir, e.g.Firmware/all_flash/all_flash.n81ap.production/iBoot.n81ap.RELEASE.img3, where the "n81ap", "k90", etc.. are for the i-Device type - run xpwntool with the proper key (from elsewhere in this Wiki)
- Make sure the decryption was successful - if it is, you should see:
"iBoot for ...., Copyright 2011, Apple Inc."
if you cat (i.e. type) the file.
- remove the img3 header - the good stuff starts at offset 0x40 (i.e. 64) - using dd (skip=1 bs=64) or some other tool
- Load in IDA. Set processor to ARM. Rebase program (Edit→Segments→Rebase Program) to 0x5FF00000 (for iBoot in iOS 5). You should see something like:
ROM:5FF00000 loc_5FF00000 ; CODE XREF: ROM:5FF00078�j ROM:5FF00000 B loc_5FF00040 ; Used for Reset - This is where we start ROM:5FF00004 ; --------------------------------------------------------------------------- ROM:5FF00004 LDR PC, =sub_5FF16FB4 ; Used for Undef ROM:5FF00008 ; --------------------------------------------------------------------------- ROM:5FF00008 LDR PC, =sub_5FF16FEC ; Used for SWI ROM:5FF0000C ; --------------------------------------------------------------------------- ROM:5FF0000C LDR PC, =sub_5FF17024 ; Used for Prefabt ROM:5FF00010 ; --------------------------------------------------------------------------- ROM:5FF00010 LDR PC, =sub_5FF17060 ; Used for DataAbt ROM:5FF00014 ; --------------------------------------------------------------------------- ROM:5FF00014 LDR PC, =loc_5FF17098 ; Used for AddrExc ROM:5FF00018 ; --------------------------------------------------------------------------- ROM:5FF00018 LDR PC, =loc_5FF16F24 ; Used for IRQ ROM:5FF0001C ; --------------------------------------------------------------------------- ROM:5FF0001C LDR PC, =sub_5FF16F6C ; Probably FIQ, need to verify this ROM:5FF00020 ; --------------------------------------------------------------------------- ROM:5FF00020 SVCPL 0xF00040 ROM:5FF00020 ; --------------------------------------------------------------------------- ROM:5FF00024 off_5FF00024 DCD sub_5FF16FB4 ; DATA XREF: ROM:5FF00004�r ROM:5FF00028 off_5FF00028 DCD sub_5FF16FEC ; DATA XREF: ROM:5FF00008�r ROM:5FF0002C off_5FF0002C DCD sub_5FF17024 ; DATA XREF: ROM:5FF0000C�r ROM:5FF00030 off_5FF00030 DCD sub_5FF17060 ; DATA XREF: ROM:5FF00010�r ROM:5FF00034 off_5FF00034 DCD loc_5FF17098 ; DATA XREF: ROM:5FF00014�r ROM:5FF00038 off_5FF00038 DCD loc_5FF16F24 ; DATA XREF: ROM:5FF00018�r ROM:5FF0003C off_5FF0003C DCD sub_5FF16F6C ; DATA XREF: ROM:5FF0001C�r ROM:5FF00040 ; --------------------------------------------------------------------------- ROM:5FF00040 ROM:5FF00040 loc_5FF00040 ; CODE XREF: ROM:loc_5FF00000�j ROM:5FF00040 ADR R0, loc_5FF00000 <-- The address we rebased to ROM:5FF00044 LDR R1, =loc_5FF00000 ROM:5FF00048 CMP R0, R1 ROM:5FF0004C CMP R0, R1 ROM:5FF00050 BEQ loc_5FF0007C ... ... ROM:5FF000E8 loc_5FF000E8 ; CODE XREF: ROM:5FF000F0�j ROM:5FF000E8 CMP R0, R1 ROM:5FF000EC STRLT R2, [R0],#4 ROM:5FF000F0 BLT loc_5FF000E8 ROM:5FF000F4 LDR R0, =(_ibootStart+1) ROM:5FF000F8 MOV LR, PC ROM:5FF000FC BX R0 ; _ibootStart ROM:5FF00100 ROM:5FF00100 loc_5FF00100 ; CODE XREF: ROM:loc_5FF00100�j ROM:5FF00100 B loc_5FF00100
Where iBootStart (not the official Apple Symbol, of course) can be seen at:
ROM:5FF00BA4 _ibootStart ; CODE XREF: ROM:5FF000FC�p
ROM:5FF00BA4 ; DATA XREF: ROM:5FF000F4�o ...
ROM:5FF00BA4 PUSH {R7,LR}
ROM:5FF00BA6 MOV R7, SP
ROM:5FF00BA8 LDR R0, =aIbootStart ; "\niBoot start\n"
ROM:5FF00BAA BL loc_5FF233C4
ROM:5FF00BAE MOVS R0, #0
ROM:5FF00BB0 BL loc_5FF16E54
ROM:5FF00BB4 BL loc_5FF1570C
ROM:5FF00BB8 BL loc_5FF143A8
ROM:5FF00BBC BL unk_5FF15264
ROM:5FF00BC0 LDR R0, =aMain ; "main"
..
Flow of iBoot (1219)
iBoot is quite a complicated binary, which spawns several ARM tasks to enable the boot process:
- iBootStart (disassembly started above) - starts main (5FF00BCA) - which calls the main function at 5FF00C14
- main: Does the good stuff (loading the kernel, etc)
starts the poweroff task (5FF00EF2) - calls (sub_5FF00FD0+1)
In recovery mode (failed boot):
starts command (5FF00F0A) - calls 5FF15928
starts idleoff (5FF99F2E) - calls 5FF01060
Revisions
NOTE: 1.2b1 through 3.0b1 are not listed
iBoot-99 1.0b (Build 1A420) [Unreleased] iBoot-159 1.0 (Build 1A543a) 1.0.1 (Build 1C25) 1.0.2 (Build 1C28) iBoot-204 1.1 (Build 3A100) 1.1 (Build 3A101) 1.1.1 (Build 3A109a) iBoot-204.0.2 1.1.1 (Build 3A110a) iBoot-204.2.9 1.1.2 (Build 3B48b) iBoot-204.3.14 1.1.3 (Build 4A93) 1.1.4 (Build 4A102) iBoot-204.3.16 1.1.5 (Build 4B1) iBoot-???.??.?? 1.2b1 (Build ????) iBoot-320.20 2.0 (Build 5A347) 2.0.1 (Build 5B108) 2.0.2 (Build 5C1) iBoot-385.22 2.1 (Build 5F137) 2.1.1 (Build 5F138) iBoot-385.49 2.2 (Build 5G77) 2.2 (Build 5G77a) 2.2.1 (Build 5H11) 2.2.1 (Build 5H11a) 3.0b1 missing iBoot-594.2~1 3.0b2 (Build 7A259g) iBoot-596.6~3 3.0b3 (Build 7A280f) iBoot-596.16~2 3.0b4 (Build 7A300g) iBoot-596.20~1 3.0b5 (Build 7A312g) iBoot-596.24~1 3.0 (Build 7A341) 3.0.1 (Build 7A400) iBoot-636.26~2 3.1b1 (Build 7C97d) iBoot-636.??~? 3.1b2 (Build 7C106c) iBoot-636.47~1 3.1b3 (Build 7C116a) iBoot-636.65~2 3.1 (Build 7C144) iBoot-636.66~1 3.1.1 (Build 7C145) 3.1.1 (Build 7C146) iBoot-636.66~5 3.1.2 (Build 7D11) iBoot-636.66.33~4 3.1.3 (Build 7E18) iBoot-817.28~18 3.2 (Build 7B367) iBoot-817.29~2 3.2.1 (Build 7B405) 3.2.2 (Build 7B500) iBoot-872~12 4.0b1 (Build 8A230m) iBoot-889.3~2 4.0b2 (Build 8A248c) iBoot-889.12~2 4.0b3 (Build 8A260b) iBoot-889.19~1 4.0b4 (Build 8A274b) iBoot-889.24~4 4.0GM (Build 8A293) 4.0 (Build 8A293) 4.0.1 (Build 8A306) 4.0.2 (Build 8A400) iBoot-931.18.1~1 4.1b1 (Build 8B5080c) iBoot-931.18.15~2 4.1b2 (Build 8B5091b) iBoot-931.18.27~1 4.1 (Build 8B117) 4.1 (Build 8B118) iBoot-931.67~2 4.2b1 (Build 8C5091e) iBoot-931.71.80~1 4.2b2 (Build 8C5101c) iBoot-931.71.13~3 4.2b3 (Build 8C5115c) iBoot-931.71.16~9 4.2GM (Build 8C134) 4.2GM (Build 8C134b) 4.2.1GM (Build 8C148) 4.2.1 (Build 8C148) 4.2.1 (Build 8C148a) iBoot-931.72.14~6 4.2.5 (Build 8E128) 4.2.6 (Build 8E200) 4.2.7 (Build 8E303) 4.2.8 (Build 8E401) iBoot-931.72.14~10 4.2.9 (Build 8E501) 4.2.10 (Build 8E600) iBoot-1072.33~1 4.3b1 (Build 8F5148b) iBoot-1072.38~2 4.3b2 (Build 8F5153d) iBoot-1072.49~2 4.3b3 (Build 8F5166b) iBoot-1072.58~4 4.3GM (Build 8F190) 4.3 (Build 8F190) iBoot-1072.59~2 4.3 (Build 8F191) 4.3.1 (Build 8G4) iBoot-1072.61~2 4.3.2 (Build 8H7) 4.3.2 (Build 8H8) 4.3.3 (Build 8J2) 4.3.3 (Build 8J3) iBoot-1072.61~6 4.3.4 (Build 8K2) 4.3.5 (Build 8L1) iBoot-1219.35.80~1 5.0b1 (Build 9A5220p) iBoot-1219.40.25~4 5.0b2 (Build 9A5248d) iBoot-1219.41.11~1 5.0b3 (Build 9A5259f) iBoot-1219.42.8~1 5.0b4 (Build 9A5274d) iBoot-1219.43.9~3 5.0b5 (Build 9A5288d) iBoot-1219.43.18~3 5.0b6 (Build 9A5302b) iBoot-1219.43.27~1 5.0b7 (Build 9A5313e) iBoot-1219.43.32~15 5.0GM (Build 9A332) [Unreleased] 5.0GM (Build 9A334) 5.0 (Build 9A334) iBoot-1219.43.32~27 5.0.1b1 (Build 9A402) iBoot-1219.43.32~29 5.0.1b2 (Build 9A404) 5.0.1 (Build 9A405) 5.0.1 (Build 9A406) iBoot-1219.61.19~6 5.1b1 (Build 9B5117b) iBoot-1219.62.1~2 5.1b2 (Build 9B5127c) iBoot-1219.62.8~5 5.1b3 (Build 9B5141a) iBoot-1219.62.15 5.1 (Build 9B176) iBoot-1219.62.15~2 5.1 (Build 9B179b)
Apple TV
iBoot-931.44.21~1 4.0 4.1 (Build 8M89) iBoot-931.71.16~9 4.1 4.2 (Build 8C150) 4.1.1 4.2.1 (Build 8C154) iBoot-1072.33~1 4.2b1 4.3b1 (Build 8F5148b) iBoot-1072.38~2 4.2b2 4.3b2 (Build 8F5153d) iBoot-1072.49~2 4.2b3 4.3b3 (Build 8F5166b) iBoot-1072.59~2 4.2 4.3 (Build 8F191m) 4.2.1 4.3 (Build 8F202) 4.2.2 4.3 (Build 8F305) 4.3 4.3 (Build 8F455) iBoot-1219.35.80~1 4.4b1 5.0b1 (Build 9A5220p) iBoot-1219.40.25~4 4.4b2 5.0b2 (Build 9A5248d) iBoot-1219.41.11~1 4.4b3 5.0b3 (Build 9A5259f) iBoot-1219.43.9~3 4.4b4 5.0b5 (Build 9A5288d) iBoot-1219.43.18~3 4.4b5 5.0b6 (Build 9A5302b) iBoot-1219.43.27~1 4.4b6 5.0b7 (Build 9A5313e) iBoot-1219.43.32~21 4.4 5.0 (Build 9A334v) iBoot-1219.43.32~22 4.4.1 5.0 (Build 9A335a) 4.4.2 5.0 (Build 9A336a) iBoot-1219.43.32~29 4.4.3 5.0.1 (Build 9A405l) 4.4.4 5.0.1 (Build 9A406a) iBoot-1219.62.1~2 5.0b1 5.1b2 (Build 9B5127c) iBoot-1219.62.8~5 5.0b2 5.1b3 (Build 9B5141a) iBoot-1219.62.15~2 5.0 5.1 (Build 9B179b)
Commands used as an exploit vector
- diags: Until 2.0 beta 6, the diags command would jump to code at the address provided to it. For example, if you sent "diags 0x9000000", it would directly jump to the code at 0x9000000. There is now a check that only allows engineering devices to utilize this backdoor.
- arm7_go: For firmware 2.1.1, the iPod touch 2G iBoot contains the ARM7 Go command, which could be used to run a payload on the ARM7 in the device.
OpeniBoot
There is an open source version of iBoot designed so that custom kernels can be run on the iPhone/iPod/iPad. You can check out the source here. It is VERY useful if you are ever reversing iBoot and do not feel like finding out what certain hardware registers are yourself. OpeniBoot currently supports all S5l8900, S5l8720, S5l8920 and S5l8930 devices. More info can be found about OpeniBoot and Linux on these devices on the iDroid-Project website.
Remappings
// n88 (3GS) 0x4FF00000 => 0x0 0x40000000 => 0xC0000000
