IBoot explained

iBoot
Developer:Apple Inc.
Operating System:Darwin, macOS,[1] iPadOS and iOS
Platform:x86, ARM
Genre:Boot loader
License:Proprietary software

iBoot is the stage 2 bootloader for all Apple products.[2] It replaces the old bootloader, BootX. Compared with its predecessor, iBoot improves authentication performed in the boot chain.[3]

For x86-based Macs, the boot process starts by running code stored in secured UEFI Boot ROM (stage 1). Boot ROM has two primary responsibilities: to initialize system hardware and to select an operating system to run (the POST and UEFI component). For ARM-based Macs, the Boot ROM does not include UEFI.[4]

For iPhones, iPads and ARM-based Macs, the boot process starts by running the device's Boot ROM. The Boot ROM loads the (LLB), which is the stage 1 bootloader and loads iBoot. If all goes well, iBoot will then proceed to load the iOS, iPadOS or macOS kernel as well as the rest of the operating system.[5] [6] If the iBoot fails to load or fails to verify iOS, iPadOS or macOS, the bootloader jumps to DFU (Device Firmware Update)[7] mode; otherwise it loads the remaining kernel modules. Since Apple A7 and Apple M1, the LLB is stored on NAND flash of iPhone or iPad, or SSD of Apple Silicon Mac.

On x86 Macs, iBoot is located in /System/Library/CoreServices/boot.efi.[8] Once the kernel and all drivers necessary for booting are loaded, the boot loader starts the kernel’s initialization procedure. At this point, enough drivers are loaded for the kernel to find the root device.[9]

Memory safety

Apple has modified the C compiler toolchain that is used to build iBoot in order to advance memory safety since iOS 14. This advancement is designed to mitigate entire classes of common memory corruption vulnerabilities such as buffer overflows, heap exploitations, type confusion vulnerabilities, and use-after-free attacks. These modifications can potentially prevent attackers from successfully escalating their privileges to run malicious code, such as an attack involving arbitrary code execution.[10]

Source code leak incident

in 2018, a portion of iBoot source code for iOS 9 was leaked on GitHub,[11] Apple then issued a copyright takedown request (DMCA) to GitHub to remove the repository. It was believed an Apple employee was responsible for the leak. However, this was not confirmed by Apple.

External links

Notes and References

  1. Web site: Darwin 9.2 Source Code. Apple Inc.. January 19, 2020. September 21, 2020. https://web.archive.org/web/20200921020149/https://opensource.apple.com/release/mac-os-x-1052.html. dead.
  2. Book: Hayes, Darren R.. A Practical Guide to Computer Forensics Investigations. 2014-12-17. Pearson IT Certification. 9780132756150. en.
  3. Book: The New Codebreakers: Essays Dedicated to David Kahn on the Occasion of His 85th Birthday. Ryan. Peter Y. A.. Naccache. David. Quisquater. Jean-Jacques. 2016-03-17. Springer. 9783662493014. en.
  4. Web site: boot process for T2, M1, and iOS devices.
  5. Web site: iOS Security Guide. Apple Inc.. May 2016. apple.com. live. https://web.archive.org/web/20160227071343/http://www.apple.com/business/docs/iOS_Security_Guide.pdf. February 27, 2016. mdy-all.
  6. Web site: Boot process for a Mac with Apple silicon - Apple Support. Jan 2024.
  7. Web site: iFixit Support: DFU Restore. iFixit. en. 2019-09-29.
  8. Web site: rEFIt - The Intel Mac boot process. refit.sourceforge.net. 2017-08-26.
  9. Web site: The Early Boot Process. developer.apple.com. en. 2017-08-26.
  10. Web site: Memory safe iBoot implementation . Apple Platform Security . Apple . 25 January 2023.
  11. News: Apple confirms iPhone source code leak . BBC News . 9 February 2018 .