darwin-xnu-build

This repository contains scripts to build xnu as well as generate a kernel collection and CodeQL databases.

Supported OS Versions

[!NOTE] CodeQL DBs built with MACHINE_CONFIG=VMAPPLE
MacOS 14.3 booted:

• via Virtualization.framework with MACHINE_CONFIG=VMAPPLE
• via qemu with ARCH_CONFIG=x86_64
• via ASi tested with MACHINE_CONFIG=T8101 and MACHINE_CONFIG=T6000

Known Issue ⚠️

Currently MACHINE_CONFIG=T8103 is not correctly building for at least 14.3

[!NOTE] When attempting to boot try adding the boot-arg: sudo nvram boot-args="-unsafe_kernel_text"

Why? 🤔

I'm hoping to patch and build the xnu source in interesting ways to aid in research and development of macOS/iOS security research tools as well as generate CodeQL databases for the community to use.

Getting Started

Dependencies

• homebrew
  • jq
  • gum
  • xcodes
  • ipsw
  • cmake
  • ninja
• XCode
• python3
• codeql CLI

[!NOTE] The build.sh script will install all these for you if you are connected to the internet.

Clone the repo

git clone https://github.com/blacktop/darwin-xnu-build.git
cd darwin-xnu-build

❯ ./build.sh --help

Usage: build.sh [-h] [--clean] [--kc]

This script builds the macOS XNU kernel

Where:
    -h|--help       show this help text
    -c|--clean      cleans build artifacts and cloned repos
    -k|--kc         create kernel collection (via kmutil create)

Build the kernel and kernel Collection

KERNEL_CONFIG=RELEASE ARCH_CONFIG=ARM64 MACHINE_CONFIG=T6000 ./build.sh --kc

[!NOTE] Supported KERNEL_CONFIG include:

• RELEASE
• DEVELOPMENT

Supported MACHINE_CONFIG include:

• T8101
• T8103
• T6000
• VMAPPLE

<SNIP>
 ⇒ 📦 Building kernel collection for 'kernel.release.t6000'
   • Decompressing KernelManagement kernelcache
Merged LINKEDIT:
  weak bindings size:          0KB
  exports info size:           0KB
  bindings size:               0KB
  lazy bindings size:          0KB
  function starts size:       41KB
  data in code size:           0KB
  symbol table size:        3702KB (85348 exports, 87979 imports)
  symbol string pool size:  6465KB
LINKEDITS optimized from 30MB to 10MB
time to layout cache: 0ms
time to copy cached dylibs into buffer: 1ms
time to adjust segments for new split locations: 2ms
time to bind all images: 8ms
time to optimize Objective-C: 0ms
time to do stub elimination: 0ms
time to optimize LINKEDITs: 2ms
time to compute slide info: 1ms
time to compute UUID and codesign cache file: 1ms
  🎉 XNU Build Done!

Check that the output contains all the KEXTs

❯ ipsw macho info build/oss-xnu.kc | head
Magic         = 64-bit MachO
Type          = FILESET
CPU           = AARCH64, ARM64e
Commands      = 241 (Size: 17160)
Flags         = None
000: LC_UUID                     67DF7148-8EEC-B1A6-5F51-7502DADF2264
001: LC_BUILD_VERSION            Platform: unknown, SDK: 0.0
002: LC_UNIXTHREAD               Threads: 1, ARM64 EntryPoint: 0xfffffe0007ad1488
003: LC_DYLD_CHAINED_FIXUPS      offset=0x003690000  size=0x444
004: LC_SEGMENT_64 sz=0x00008000 off=0x00000000-0x00008000 addr=0xfffffe0007004000-0xfffffe000700c000 r--/r--   __TEXT
<SNIP>

Clean rebuild the kernel and kernel collection

KERNEL_CONFIG=RELEASE ARCH_CONFIG=ARM64 MACHINE_CONFIG=T6000 ./build.sh --clean --kc

Generate a CodeQL database

./codeql.sh

<SNIP>
[2023-03-03 22:33:20] [build-stdout]   🎉 XNU Build Done!
Finalizing database at darwin-xnu-build/xnu-codeql.
Running TRAP import for CodeQL database at darwin-xnu-build/xnu-codeql...
TRAP import complete (1m46s).
Successfully created database at darwin-xnu-build/xnu-codeql.
[info] Deleting log files...
[info] Zipping the CodeQL database...
  🎉 CodeQL Database Create Done!

Script builds and zips up the CodeQL database

❯ ll xnu-codeql.zip
-rw-r--r--@ 1 blacktop  staff   219M Mar  3 22:35 xnu-codeql.zip

Generate a CodeQL database (in a local Tart VM)

Install deps: packer, tart and cirrus

make deps

Build VM image

make build-vm

Create CodeQL DB

make codeql-db

 > Building CodeQL Database
🕓 'Build' Task 08:22
   ✅ pull virtual machine 0.0s
✅ 'Build' Task 47:59
 🎉 Done! 🎉
🕒 'Build' Task 46:28
✅ 'Build' Task 48:15

❯ tree artifacts/

artifacts/
└── Build
    └── binary
        └── xnu-codeql.zip

3 directories, 1 file

TODO

• [x] ~~Auto build xnu with Github Actions~~
• [x] ~~Auto generate CodeQL database with Github Actions~~

NOTES

To see kernel logs

log show --debug --last boot --predicate 'process == "kernel"'

Credit

• https://github.com/pwn0rz/xnu-build
• https://kernelshaman.blogspot.com/2021/02/building-xnu-for-macos-112-intel-apple.html