Disassembling Apple Exclaves

7 min readApr 6, 2025

Corrections to prior posts

Much of the functionality of Exclaves I covered previously (eg. Conclaves, Services etc) references the “XnuProxy”. This is a component running in user mode in the secure world.
In my first post on Exclaves, I suggested that the Secure Kernel may be based on seL4 because it contained strings referencing capabilities and other seL4 type objects. Posting on Bluesky, none other than Gernot Heiser himself (should that be “Himself”? 😊) said that SK almost certainly wouldn’t be seL4 (which would have been a GPL violation) but perhaps a clone. After further thought, I’ve realised that Apple could have simply taken some ideas from seL4 but developed their own flavour of L4, modified to suit their needs - perhaps even through modifications to their original cL4 kernel.
As already mentioned in a previous update post, Exclaves are implemented using the existing guarded execution privilege levels (GL0/1/2) rather than ARM TrustZone. More on this below, now that I have started disassembling it!

New Disassembly Discoveries!!

This section bought to you by … Microsoft! My [yes, old] PC running Windows 10 was going to be replaced by a Mac once Win10 support ended later this year. However the power supply died a few weeks ago and I’m now a happy Mac Mini owner 6 months early. I have a unix shell, and vi as an editor and am in heaven ;)

I’m new to this, but I have been slowly doing some small areas of disassembly related to Exclaves. It has very much helped to follow the prior work of other people on this. I’m doing this out of personal curiosity and impatience ;)

SPTM “Subsystems”

Dataflow forensics previously identified “subsystems” within SPTM. In iOS 18 there is now a new subsystem #9, which is identified as the CPUTRACE subsystem containing five calls.
Dataflow forensics also found two un-identified subsystems, #2 (with three calls) and #4 which was unimplemented in iOS17. Now in iOS 18, I have found that both of these are subsystems used by the Secure Kernel! Subsystem #4 contains two calls.
Like XNU, the Secure Kernel also has individual calls to SPTM subsystems #253, #254, and #255. The instruction following these calls is a HALT so I expect these are shutdown or panic type calls.

XNU and SPTM

As we already know:

XNU runs in EL1/2
XNU uses GENTER to switch to SPTM in GL2
SPTM uses GEXIT to return to EL2

Secure Kernel / cL4

Secure Kernel runs in GL1 due to its ability to modify GL1/2 system registers.
Secure Kernel calls “up” to SPTM (GL2) via a hypervisor HVC #0 instruction, with the subsystem&call parameter in register X16 (remember from the above, this will be one of three calls from subsystem #2, or two calls from subsystem #4). This is a mirror of XNU except it uses HVC instead of GENTER, as SK is already running in the guarded execution world.
Secure Kernel contains ERET calls, which indicate it receives system calls to return (from GL0 rather than EL0 I assume). And indeed, examining many of the binaries that run in Exclaves, they do make system calls.

SK userspace— Exclaves and TXM

These system calls from Exclaves to SK come in the form of SVC #0 through to SVC #5. The system call numbers do not match up with either XNU’s Mach Trap or BSD syscall numbers. At this point, I think this indicates six different SVC calls are available within Exclaves (running in GL0), to call into the Secure Kernel (in GL1).
I haven’t delved too deep yet, but I saw SVC #4 and SVC #5 called by the exclaves “roottask”, in a very tight loop waiting until X0 != 1.
TXM still uses SVC #37, #38, and #0. Dataflow forensics identified these as going to SPTM in iOS 17. I haven’t checked (yet), but these must now be intercepted by SK, even if it is just forwarding #37 and #38 onwards. I do wonder if one of SK’s two SPTM subsystems is for TXM, and the other is for Exclaves.

Domains and Resources in the Root table

My first post listed some of the contents of the exclaves root table that had been discovered from the XNU side, however I have now extracted a much more complete list of domains and resources. Remember, a conclave can contain many resources of various types (such as services or buffers), and every conclave must have a conclave manager in the com.apple.kernel domain. This gives a fairly complete picture of everything that Apple is currently using Exclaves for!


com.apple.audiomxd.conclave:    
  com.apple.audio.lpmic
  com.apple.audio.mic
  com.apple.audiomxd.AudioCaptureServer
  com.apple.audiomxd.MTDAudioDSPControl
  com.apple.audiomxd.PerceptionAudioDSPControl
  com.apple.audiomxd.SharedAudioDSPControl
  com.apple.audiomxd.SiriAudioDSPControl
  com.apple.audiomxd.SoundAnalysisAudioDSPControl
  com.apple.inbound_buffer.hpmic_injection
  com.apple.inbound_buffer.hpmic16_injection
  com.apple.inbound_buffer.muted_talker_detection_ref_stream
  com.apple.inbound_buffer.perception_ref_stream
  com.apple.inbound_buffer.shared_audiodsp_ref_stream
  com.apple.inbound_buffer.siri_ref_stream
  com.apple.inbound_buffer.sound_analysis_ref_stream
  com.apple.notification.audiocapture
  com.apple.notification.audiodsp
  com.apple.notification.audiodsp.analysis
  com.apple.sensors.mic


com.apple.backboardd.conclave:            
  com.apple.backboardd.ExclaveFDRDecodeRawDataStoreKitService
  com.apple.backboardd.AppleProxExclaveService
  com.apple.backboardd.SILManager

com.apple.cameracaptured.conclave:             
  com.apple.cameracaptured.ISPIRManager         
  com.apple.cameracaptured.ISPRGBManager           
  com.apple.cameracaptured.ISPIRService           
  com.apple.cameracaptured.ISPRGBService

com.apple.conclave.mediaserverd:               
  com.apple.mediaserverd.ISPIRManager        
  com.apple.mediaserverd.ISPRGBManager           
  com.apple.mediaserverd.ISPIRService          
  com.apple.mediaserverd.ISPRGBService

com.apple.conclave.test1:
  com.apple.service.ExclavesCHelloServer

com.apple.corespeechd.conclave:                
  com.apple.corespeechd.SiriVoiceTriggerService            
  com.apple.isolatedcoreaudioclient.service               
  com.apple.audio.siri_history                      
  com.apple.sensors.mic

com.apple.darwin:
  com.apple.service.ANEEngine
  com.apple.service.ANEExclave  
  com.apple.service.ANEExclave_EDK
  com.apple.service.ANEExclaveTestClient
  com.apple.service.AudioDriver 
  com.apple.service.AudioDriver_EDK
  com.apple.service.AudioDriverLPMic
  com.apple.service.AudioDriverLPMic_EDK
  com.apple.service.AudioDriverVT
  com.apple.service.AudioDriverVT_EDK
  com.apple.service.AudioSharedDARTMapper
  com.apple.service.AudioSharedDARTMapper_EDK
  com.apple.service.EXBrightCore
  com.apple.service.EXBrightCore_EDK
  com.apple.service.ExclaveDriverKit
  com.apple.service.ExclaveFDRDecodeTestClientExclave
  com.apple.service.ExclaveSEPManager
  com.apple.service.ExclaveSEPManager_EDK
  com.apple.service.ExclaveSEPTestClient
  com.apple.service.ExclaveTestService
  com.apple.service.EXDisplayPipeDriver_EDK_xnuproxy
  com.apple.service.EXDisplayPipeDriver_xnuproxy
  com.apple.service.HelloDrivers
  com.apple.service.HelloExclaveCxx
  com.apple.service.HelloExclaveKit
  com.apple.service.HelloStorage
  com.apple.service.HPMic16Device
  com.apple.service.HPMic16Device_EDK
  com.apple.service.HPMic16DMA  
  com.apple.service.HPMic16DMA_EDK
  com.apple.service.HPMicAudioDriver
  com.apple.service.HPMicAudioDriver_EDK
  com.apple.service.SecureRTBuddyAOP
  com.apple.service.SecureRTBuddyAOP_EDK
  com.apple.service.SecureRTBuddyAOP_IOReporting
  com.apple.service.SecureRTBuddyDCP
  com.apple.service.SecureRTBuddyDCP_EDK
  com.apple.service.SecureRTBuddyDCP_IOReporting
  com.apple.service.TightbeamTestsServer
  com.apple.service.user_app    
  com.apple.service.user_app2   
  com.apple.service.user_app3

com.apple.exclavetestrunnerd.conclave:
  com.apple.exclavetestrunnerd.service

com.apple.facekittestd.conclave:
  com.apple.facekittestd.service

com.apple.isolatedaudiometerclientd.conclave:  
  com.apple.isolatedaudiometerclientd.service
  com.apple.isolatedcoreaudioclient.service

com.apple.kernel:
  com.apple.audio.lpmic
  com.apple.audio.mic
  com.apple.audio.siri_history
  com.apple.audio.test
  com.apple.audiomxd.conclave
  com.apple.backboardd.conclave
  com.apple.cameracaptured.conclave
  com.apple.conclave.mediaserverd
  com.apple.conclave.test1
  com.apple.corespeechd.conclave
  com.apple.exclavetestrunnerd.conclave
  com.apple.facekittestd.conclave
  com.apple.inbound_buffer.exfiltration
  com.apple.inbound_buffer.hpmic_injection
  com.apple.inbound_buffer.hpmic16_injection
  com.apple.inbound_buffer.muted_talker_detection_ref_stream
  com.apple.inbound_buffer.siri_ref_stream
  com.apple.inbound_buffer.sound_analysis_ref_stream
  com.apple.isolatedaudiometerclientd.conclave
  com.apple.mobileassetd.conclave
  com.apple.named_buffer.1
  com.apple.named_buffer.10
  com.apple.named_buffer.112
  com.apple.named_buffer.113
  com.apple.named_buffer.16
  com.apple.named_buffer.2
  com.apple.named_buffer.3
  com.apple.named_buffer.32
  com.apple.named_buffer.36
  com.apple.named_buffer.4
  com.apple.named_buffer.41
  com.apple.named_buffer.6
  com.apple.named_buffer.7
  com.apple.notification.audiocapture
  com.apple.notification.audiodsp
  com.apple.notification.audiodsp.analysis
  com.apple.notification.hello
  com.apple.outbound_buffer.exfiltration
  com.apple.perceptiond.conclave
  com.apple.securdled.conclave
  com.apple.sensors.cam
  com.apple.sensors.cam_alt_faceid
  com.apple.sensors.cam_alt_faceid_delayed
  com.apple.sensors.mic
  com.apple.service.ConclaveLauncherControl
  com.apple.service.ConclaveLauncherDebug
  com.apple.service.ExclaveIndicatorController
  com.apple.service.ExclaveKeyStoreTestClient
  com.apple.service.ExclavesCHelloServer
  com.apple.service.Exfiltration_xnuproxy
  com.apple.service.FrameMint
  com.apple.service.HelloDriverInterrupts
  com.apple.service.ISPCamEngine
  com.apple.service.ISPCamEngine_EDK
  com.apple.service.ISPEngine
  com.apple.service.ISPEngine_EDK
  com.apple.service.LogServer_xnuproxy
  com.apple.service.PanicInit
  com.apple.service.Stackshot
  com.apple.shareddspd.conclave
  com.apple.sharedmem.stackshotserver
  com.apple.soundanalysisd.conclave
  com.apple.storage.backend

com.apple.mobileassetd.conclave:               
  com.apple.mobileassetd.service

com.apple.perceptiond.conclave:                
  com.apple.perceptiond.services             
  com.apple.isolatedcoreaudioclient.service

com.apple.securdled.conclave:
  com.apple.securdled.service

com.apple.shareddspd.conclave:
  com.apple.isolatedcoreaudioclient.service

com.apple.soundanalysisd.conclave:
  com.apple.soundanalysisd.service             
  com.apple.isolatedcoreaudioclient.service

I noticed that some resources have duplicates — they appear both in a conclave domain and also in com.apple.kernel. These are all buffers, notifications and sensors. It appears these types of resources can be in more than one domain.

ExclaveCore

ExclaveCore consists of the Secure Kernel plus a number of other OS binaries, in a ~43MB .img4 file. The kernel binary itself is only 229KB, with only about 68KB of this being executable text! -

Minnie 22D82__iPhone17,1/Firmware/image4/SYSTEM> disarm -l kernel
Opened companion file kernel.ARM64.3BB4444D-5A7C-3146-90B5-1A33C51C4800
0x4000-0x18000 -> 0xffffff8000000000-0xffffff8000014000 __TEXT               (TEXT,READ-ONLY, 81920 bytes)
 0x4000-0x41b0 -> 0xffffff8000000000-0xffffff80000001b0 __TEXT.__head        (TEXT,READ-ONLY, 432 bytes)
 0x4800-0x145cc -> 0xffffff8000000800-0xffffff80000105cc __TEXT.__text        (TEXT,READ-ONLY, 64972 bytes)
 0x145d0-0x15020 -> 0xffffff80000105d0-0xffffff8000011020 __TEXT.__const       (DATA,READ-ONLY, 2640 bytes)
 0x15020-0x15974 -> 0xffffff8000011020-0xffffff8000011974 __TEXT.__cstring     (TEXT,READ-ONLY, 2388 bytes)
0x18000-0x1c000 -> 0xffffff8000014000-0xffffff8000018000 __DATA               (DATA, 16384 bytes)
 0x18000-0x18130 -> 0xffffff8000014000-0xffffff8000014130 __DATA.__data        (DATA, 304 bytes)
 0x1c000-0x1d9e0 (not mapped) symbol table         (6624 bytes)
 0x1d9e0-0x1f990 (not mapped) string table         (8112 bytes)

ExclaveCore includes a small number of binaries aside from the kernel, these are all MachO arm64e 64 bit executables, like SK. They do not run in kernel mode as SK is a microkernel — all of these are found to perform SVC calls to SK.

ExclaveKit

This is where the code, resources and frameworks for Exclaves themselves live. ExclaveKit is approximate 514MB in size. The basic directory structure is:

A small number of dylibs (42 libraries, 17.4MB) are located within ExclaveKit under /usr/lib.

Public frameworks in ExclaveKit are:

Private Frameworks in ExclaveKit:

It should be noted that there are many Exclave related frameworks within iOS as well. These provide the necessary methods to interact with functionality walled off inside the actual Exclaves.

ExclaveOS

ExclaveOS is presumedly the combination of ExclaveCore and ExclaveKit.

XRT

I still haven’t figured out what “XRT”, which is a frequent prefix in variable and function names, stands for. Is the X for Xnu or eXclave? Is RT for “real time” or “run time”? Or something else?

Xrt even gets its own ASCI-art in the ExclaveOS sharedcache binary!

disarm -r __TEXT.__cstring /Firmware/image4/APP/sharedcache | grep -A13 0x8ad3993

0x8ad3993: exclaves_allow_unlimited_early_crashes
0x8ad39ba: panic_on_conclave_exception_triage
0x8ad39e0: [CONCLAVE LAUNCHER 
0x8ad3a00: State transition: 
0x8ad3a20: Not Booted, needs storage
0x8ad3a40: ConclaveLauncherEntry()
0x8ad3a60: __   _______ _______
\ \ / /  __ \__   __|
 \ V /| |__) | | |
  > < |  _  /  | |
 / . \| | \ \  | |
/_/ \_\_|  \_\ |_|___Conclavelauncher 
0x8ad3af0: ConclaveLauncherPseudoComponent/conclave-launcher.swift
0x8ad3b30: [Conclave Launcher] could not get resource data
0x8ad3b60: could not get data from EASM server resource collection

That wraps it up for now. My next post is hopefully about this whole concept of retrofitting microkernel-like isolation onto an existing OS. There is some prior art on this which I have been looking at, but it leads to questions of where exactly Apple is heading.

This post was based on the iPhone17,1_18.3.2_22D82_Restore.ipsw image.