UniXNU/docs/concepts/security.md

Integrity and boot policy

UniXNU keeps the original Apple security components and supplies the inputs they check. The source kernel adds the platform code those components need, and the boot payload supplies the trust caches and device tree properties that describe the device.

Inputs

Input	Supplier
Trust cache bundle	--trust-cache FILE
Trust cache pins	[payload] trust_cache_sha256
Platform seed	--unique-chip-id HEX
Device tree identity	Format 2 typed [adt] tables; format 1 board script
PMGR integration	XNU_SHENG_PMGR on boards that need it
Root policy	XNU_VERIFIED_ROOT_PROBE, XNU_OWNER_ROOT_AUDIT, XNU_OWNER_ROOT_TRUST

Trust cache

DarwinBoot validates the structure of the trust cache bundle and copies it into the kernel window. The ADT /chosen/memory-map/TrustCache placeholder receives the address and size.

The kernel patch native-trust-cache-runtime initializes the runtime trust cache path on BCM2837. The original AppleImage4 and AMFI components validate code against the cache.

The payload step accepts a trust cache bundle only when its SHA-256 is listed in [payload] trust_cache_sha256.

Code signing at 4 KiB

The original CodeDirectory uses a 16 KiB hash page. A 4 KiB kernel validates 4 KiB pages. The patch native-4k-signature-hash-cache:

1. Reads every original 16 KiB block through vn_rdwr.
2. Checks the block against the original CodeDirectory hash.
3. Derives one hash per 4 KiB page from the verified block.
4. Stores the derived hashes in read-only kernel memory.
5. Serves cs_validate_page from the derived table.

A block is published only after the original 16 KiB hash matches. A failed block leaves the blob without a derived table, and the page validator returns CS_VALIDATE_TAINTED.

AMFI policy

The ADT property /chosen/amfi-only-platform-code keeps AMFI in its platform code policy. The early_security_init entry in [kernel.prelink] runs the original AppleMobileFileIntegrity initializer at the selected address.

The kernel patches offline-owner-root-* add the owner root checks used by the first boot path:

Patch	Function
offline-owner-root-binding-audit	Checks the root binding against the boot manifest
offline-owner-root-crypto-probe	Checks the owner crypto provider
offline-owner-boot-manifest	Records the boot manifest hash
offline-owner-cache-carrier	Selects the code signing cache carrier
offline-owner-systemos-mount	Mounts the SystemOS cryptex
offline-owner-z-air-init	Initializes the Z air path for the owner root

GPU client grant

Adreno740 publishes NativeSandboxGrantProcess on its accelerator service. The patch zzw-native-adreno-sandbox-grant compares the opening process name with that property. The named process opens the user client past mac_iokit_check_open_service and mac_iokit_check_open. The render server is the named process.

Verified root

kits/VerifiedRoot supplies a signed policy bundle. The verified block driver checks every read against the policy. The policy can be selected per capacity with --verified-root-bundle.

The kit provides:

Tool	Function
verified_root.c	Policy parsing and read authentication
xnu_crypto.c	XNU crypto adapter
manifest.py	Policy bundle builder
verify_image.py	Image verification

Storage integrity

VirtioMmioBlock and RamBlock share the verified block policy. The build script checks that both transports import the same original storage bindings and that the compiled object matches the recorded hash.

Reporting

The payload report records:

Field	Meaning
kernel_sha256	Input kernel
payload_kernel_sha256	Kernel in the payload, after the optional panic screen patch
adt_sha256	ADT sidecar
trust_cache_sha256	Trust cache bundle
data_ramdisk_sha256	Data seed
payload_sha256	Payload image

The boot manager log records the staged kexts, the installed ACPI tables and the injected drivers.

Next steps

• Payload describes the trust cache and Data inputs.
• Patch reference lists the security patches.
• Boot arguments lists the security related arguments.