A Reverse Engineer's Anatomy of the macOS Boot Chain and Security Architecture
Mood
informative
Sentiment
neutral
Category
research
Key topics
MacOS
Boot Chain
Security Architecture
Reverse Engineering
Discussion Activity
Moderate engagementFirst comment
3h
Peak period
7
Hour 9
Avg / period
2.9
Based on 43 loaded comments
Key moments
- 01Story posted
Nov 22, 2025 at 3:54 PM EST
1d ago
Step 01 - 02First comment
Nov 22, 2025 at 7:18 PM EST
3h after posting
Step 02 - 03Peak activity
7 comments in Hour 9
Hottest window of the conversation
Step 03 - 04Latest activity
Nov 23, 2025 at 11:20 PM EST
3h ago
Step 04
Generating AI Summary...
Analyzing up to 500 comments to identify key contributors and discussion patterns
I'm also not sure if it's 100% accurate. My (possibly wrong) understanding of the guarded execution feature is that each GL is paired with a normal ARM EL. i.e. GL2 constrains EL2, GL1 constrains EL1, etc. XNU lives in EL2 so SPTM lives in GL2, and GENTER/GEXIT move you between ELx and GLx through a secure call vector. In contrast, this guide refers to GL0 being the "standard XNU kernel context" even though XNU lives in EL2 on macOS. Furthermore, on device OSes (iOS/iPadOS/etc) they put a second kernel in GL1 and various enforcement policy tools (i.e. code signing policy, camera indicator policy) in GL0[0]. So I'm not sure how macOS putting XNU in GL0 makes sense?
[0] XNU source refers to this concept as an Exclave, which itself can be grouped with other isolated resources as a Conclave.
For example, it says quite unambiguously that the bootloader is encrypted directly with the GID key (loading the LLB ciphertext into the AES engine), but that's not how it works, the GID key is used to decrypt the LLB's KBAG into an AES key:IV pair and that is used to decrypt the LLB.
More:
> The behavior of the Boot ROM changes fundamentally based on the "Security Domain" fuse. > > Production (CPFM 01):
Security Domain (SDOM) is a different thing than CPFM. And production devices have CPFM 03.
> CHIP (Chip ID): Identifies the SoC model (e.g., 0x8101 for M1).
The M1 SoC is 0x8103.
Due to Brandolini's Law I will not continue to list everything else that is wrong here...
New strategy discovered: Ask LLM to write article, nerdsnipe HN into correcting it, feed corrections back into LLM until people stop complaining
I suspected LLM rewriting or generation but I don't possess enough knowledge into how the Apple pre-boot environment works to make an accurate judgement on the accuracy of the post. But I definitely had very strong suspicions of LLM influence with all the bullet lists and hem-hawing the post does; I would expect that someone who successfully reverse engineered the boot chain this thoroughly wouldn't need to hedge anything but Apple's rationale on why they did things. But maybe I'm too overly focused on details.
The large amount of rewriting being done within 5 minutes is another sign of LLM...
This quickly went from Brandolini's Law to Cunningham's Law. Learn how Apple's boot process works by explaining it wrong and waiting for people to correct you!
I have met multiple brilliant, very bright, and talented people (mathematicians, physicists, doctors) who excel at what they know and do, yet immensely struggle to spell, write, or both. There are also people who do not like to write (whatever the reason is).
GenAI has been a great boon for such a type of person as it dissolves their struggle – they convey the idea to the machine (however awful the scribe is) and GenAI handles the grammar and style.
Granted, it is different from «hey, GenAI pet, write me a blog post on XYZ».
Sometimes people mix up “i.e.” (“id est”; “that is”) and “e.g.” (“exempli gratia”; “for example”).
Of course, only the author knows if this case was a mix up, or if they really wrote what they meant.
I have never seen this frequency before.
I think the author might have left an LLM agent in a loop fixing it whenever HN points out an error or finds something new to add on the internet.
You also don't have "kernel access" in macOS. After boot, the memory region corresponding to the macOS kernel is marked as read-only at the memory controller level.
Does that work for USB boot?
> You also don't have "kernel access" in macOS. After boot, the memory region corresponding to the macOS kernel is marked as read-only at the memory controller level.
You can turn that off from recovery mode. (see `bputil`) It's needed to use dtrace.
Recently I've taken on their code signing component. The concepts they've created, such as identifying applications by their "designated requirements" is a stroke of genius. It makes the system completely stateless and capable of almost anything without auxiliary data structure or additional code.
I've seen other engineering teams try and fail at building something similar, and never with such powerful simplicity.
cough iMessage, hardware backdoors cough
"In this case, the federal government prohibited us from sharing any information," the company said in a statement. "Now that this method has become public we are updating our transparency reporting to detail these kinds of requests."
“At Apple, we are always working to defend our users against even the most complex cyberattacks. The steps we’re taking today will send a clear message: in a free society, it is unacceptable to weaponise powerful state-sponsored spyware against those who seek to make the world a better place,”
"The app in question is called “LassPass Password Manager” and lists Parvati Patel as the developer. The app attempts to copy our branding and user interface..."
Final Thought: macOS is no longer just a Unix system. It is a distributed system running on a single die, governed by a hypervisor that doesn't exist in software. The kernel is dead; long live the Monitor.
Want the full context?
Jump to the original sources
Read the primary article or dive into the live Hacker News thread when you're ready.