T8012

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T8012, also just known as the T2 is the CPU introduced in the second-generation iBridge processor, the processor found on the iMac Pro, and used on all subsequent T2 enabled Mac products.

Enabled Mac Products

Devices sourced from [1] and [2]

iBridge Product ID Board ID Board Minor Description (Product ID) checkm8/blackbird confirmed
iBridge2,1 J137AP 0x0A Apple T2 iMacPro1,1 (j137) yes
iBridge2,3 J680AP 0x0B Apple T2 MacBookPro15,1 (j680) yes
iBridge2,4 J132AP 0x0C Apple T2 MacBookPro15,2 (j132) yes
iBridge2,5 J174AP 0x0E Apple T2 Macmini8,1 (j174) yes
iBridge2,6 J160AP 0x0F Apple T2 MacPro7,1 (j160) yes
iBridge2,7 J780AP 0x07 Apple T2 MacBookPro15,3 (j780) yes
iBridge2,8 J140kAP 0x17 Apple T2 MacBookAir8,1 (j140k) yes
iBridge2,10 J213AP 0x18 Apple T2 MacBookPro15,4 (j213) yes
iBridge2,11 J230AP 0x1F ? ?
iBridge2,12 J140aAP 0x37 Apple T2 MacBookAir8,2 (j140a) yes
iBridge2,13 J214AP 0x1E ? ?
iBridge2,14 J152fAP 0x3A Apple T2 MacBookPro16,1 (j152f) yes
iBridge2,15 J230kAP 0x3F Apple T2 MacBookAir9,1 (j230k) yes
iBridge2,16 J214kAP 0x3E Apple T2 MacBookPro16,2 (j214k) ?
iBridge2,19 J185AP 0x22 Apple T2 iMac20,1 (j185) ?
iBridge2,20 J185fAP 0x23 Apple T2 iMac20,2 (j185f) ?
iBridge2,21 J223AP 0x3B Apple T2 MacBookPro16,3 (j223) ?
iBridge2,22 J215AP 0x38 Apple T2 MacBookPro16,4 (j215) ?

T2 Recovery USB Device ID

During the restore process, the T2 presents as a Restore Mode com.apple.recoveryd service, but uses the USB product ID of 0x8086 instead of the iPhone's 0x1290-0x12AF.[3]

Bootrom Exploits

The T8012 uses Bootrom version Bootrom_3401.0.0.1.16 which is vulnerable to checkm8. A fork of checkm8 with support for the t2 exists at h0m3us3r and a checkra1n with T2 tutorial is at t8012 blog. The adaption of checkm8 was performed by the t8012 checkm8 group by brute forcing the various locations from ROM. The copyright string reads SecureROM for t8012si, Copyright 2007-2016, Apple Inc, for version Bootrom_3401.0.0.1.16.

Similar to iPhones, iPads, and iPods, iBridge firmware bundles come in IPSW form. Build train codenames are appended with "HWBridge" to distinguish them from normal firmwares, and the disk image files inside have labels that are appended with "UniversalBridgeOS." They can only be restored to if the Mac is in DFU mode.

The T2 Secure Enclave Processor (SEP)

The T2 is based on the A10 silicon design and therefore has a A10 SEP. The A10 SEP is a ARM Cortex-A7 32bit CPU. The T2 Secure Enclave is vulnerable to the same exploit Pangu presented at MOSEC named `blackbird`.

The T2 SEP is responsible for acting as a secure store for symmetric secrets (tokens) as well as asymmetric credentials that can be generated and wrapped by the SEP. The SEP plays a key role in disk encryption.

Entering DFU Mode

The T2 models can be restored via a Thunderbolt cable using Apple Configurator 2.

Desktop Macs

For example, iMac Pro and Mac mini models from 2018 or later.[1]

  1. Completely power off the Mac; disconnect it from external power.
  2. Attach one end of a Thunderbolt cable to the correct Thunderbolt port on the Mac.
    • iMac Pro: The Thunderbolt port that is located next to the Ethernet port.
    • Mac mini: The Thunderbolt port that is located next to the HDMI port.
  3. Connect the other end to any Thunderbolt or USB port on the host Mac (the device which will be used for restoring).
  4. Hold down the power button on the back of the Mac for 3 seconds, while connecting the power cord.

Portable Macs

For example, MacBook models from 2018 or later.[2]

  1. Completely power off the Mac; disconnect it from external power.
  2. Attach one end of a Thunderbolt cable to the Thunderbolt port that is located on the left side, closest to the front.
  3. Connect the other end to any Thunderbolt or USB port on the host Mac (the device which will be used for restoring).
  4. Hold down the power button, right Shift key, and left Control and Option keys, for 3 seconds.

Identifying the T2 from DFU

Once a device is in DFU enumerating the USB device yields the BoardID. Using either Linux's lsusb -v or macOS's ioreg -p IOUSB the USB serial attribute will contain the same information as any other Apple A core iBoot device. (http://newosxbook.com/bonus/iBoot.pdf). The ChipID will always be 8012. The value for BDID is the BoardID. Full decoding of the version string can be performed using the code at https://github.com/das-iboot/das-iboot/blob/master/das_iboot/device.py. These values for BDID, CPID, CPRV and ECID are in Hex.

Identifying the T2 from macOS

This will provide many of the same values as DFU but in Decimal instead of Hex like above:

# ECID in decimal instead of Hex
/usr/libexec/remotectl get-property localbridge UniqueChipID
# Chip ID CPID in decimal (32786 == 0x8012)
/usr/libexec/remotectl get-property localbridge ChipID
# Board Revision CPRV in decimal instead of hex
/usr/libexec/remotectl get-property localbridge BoardRevision
# Board ID (BDID) in decimal instead of hex
/usr/libexec/remotectl get-property localbridge BoardId
# Hardware Model is the name of the Board
/usr/libexec/remotectl get-property localbridge HWModel
# Mac Model String
sysctl -n hw.model

Mac Configuration Utility

The Mac Configuration Utility icon.

In order to restore a firmware to an iBridge device, technicians must use two Apple Internal tools. The first one, Apple Service Toolkit (AST), is used to initiate a diagnostic session between the host Mac and the Mac in DFU mode. The second tool, which must be installed on the host Mac, is known as the Mac Configuration Utility (MCU). It communicates with AST to provide board information and initiate restores and diagnostics over-the-air. MCU supports macOS 10.13.2 or later.

The Mac Configuration Utility startup screen.

iBridge devices can still be managed if there is no firmware present by booting a diagnostic image, which is pushed to the device by MCU after a Blank Board Serializer test is initiated on AST. This test will also assign a serial number to a new board.

During a restore, an Apple logo and progress bar will show on the screen, similar to that of a normal device restore. It is unknown if iBridge firmwares are signed, or if they are verified by the host or by iBridge devices.

References