The Apple T2 (Apple's internal name is T8012)[2] security chip is a system on a chip "SoC" tasked with providing security and controller features to Apple's Intel basedMacintosh computers. It is a 64-bitARMv8 chip and runs bridgeOS.[3][4] T2 has its own RAM and is essentially a computer of its own, running in parallel to and responding to requests by the main computer that the user interacts with.
Design
The main application processor in T2 is a variant of the Apple A10, which is a 64-bitARMv8.1-A based CPU.[1] It is manufactured by TSMC on their 16 nm process, just as the A10. Analysis of the die reveals a nearly identical CPU macro as the A10 which reveals a four core design for its main application processor, with two large high performance cores, "Hurricane", and two smaller efficiency cores, "Zephyr". Analysis also reveals the same amount of RAM controllers, but a much reduced GPU facility; three blocks, only a quarter the size compared to A10.[1]
The die measures 9.6 mm × 10.8 mm, a die size of 104 mm2, which amounts to about 80% of the size of the A10.[1]
As it serves as a co-processor to its Intel based host, it also consists of several facilities handling a variety of functions not present in the host system's main platform. It is designed to stay active even if the main computer is in a halted low power mode. The main application processor in T2 is running an operating system called bridgeOS.
The secondary processor in T2 is an 32-bit ARMv7-A based CPU called Secure Enclave Processor (SEP) which has the task of generating and storing encryption keys. It is running an operating system called "sepOS" based on the L4 microkernel.[5]
The T2 module is built as a package on a package (PoP) together with its own LP-DDR4 RAM. Mac configurations with 1 TB of SSD storage or greater receive 2 GB LP-DDR4, while lower storage configurations receive 1 GB.[6]
The T2 communicates with the host via a USB-attached Ethernet port.[3]
Security features
There are numerous features regarding security, including:
A storage controller for the computer's solid-state drive, including always on, on-the-fly encryption and decryption of data to and from it.[4][8][9] As a side effect, even if the SSD uses a standardized socket and is not soldered, it still can't be replaced.
Controllers for microphones, camera, ambient light sensors and Touch ID, decoupling the main operating system's access to those.[7][8][9]
On November 7, 2018, Apple released the updated Mac mini and MacBook Air models with the T2 chip.[13][14] MacBook Air's Touch ID sensor is powered by the chip.
On August 4, 2020, a refresh of the 5K iMac was announced, including the T2 chip.[15]
The functionality of the T2 chip is incorporated in Apple's M-series CPUs, thus eliminating the need for a separate chip in Apple silicon-powered computers.[5] The T2 chip was discontinued with the completion of the Mac transition to Apple silicon in June 2023.
Security vulnerabilities
In October 2019 security researchers began to theorize that the T2 might also be affected by the checkm8 bug as it was roughly based on the A10 design from 2016 in the original iMac Pro.[16] Rick Mark then ported libimobiledevice to work with the Apple T2 providing a free and open source solution to restoring the T2 outside of Apple Configurator and enabling further work on the T2.[17] On March 6, 2020, a team of engineers dubbed T2 Development Team exploited the existing checkm8 bug in the T2 and released the hash of a dump of the secure ROM as a proof of entry.[18] The checkra1n team quickly integrated the patches required to support jailbreaking the T2.[19][20][21][22]
The T2 Development Team then used Apple's undocumented vendor-defined messages over USB power delivery to be able to put a T2 device into Device Firmware Upgrade mode without user interaction. This compounded the issue making it possible for any malicious device to jailbreak the T2 without any interaction from a custom charging device.[23][24][25]
Later in the year the release of the blackbird SEP vulnerability further compounded the impact of the defect by allowing arbitrary code execution in the T2 Secure Enclave Processor.[26] This had the impact of potentially affecting encrypted credentials such as the FileVault keys as well as other secure Apple Keychain items.
Developer Rick Mark then determined that macOS could be installed over the same iDevice recovery protocols, which later ended up true of the M1 series of Apple Macs.[27] On September 10, 2020, a public release of checkra1n was published that allowed users to jailbreak the T2.[28][29] The T2 Development Team created patches to remove signature validation from files on the T2 such as the MacEFI as well as the boot sound. Members of the T2 Development Team begin answering questions in industry Slack instances.[30] A member of the security community from IronPeak used this data to compile an impact analysis of the defect, which was later corrected to correctly attribute the original researchers[31] The original researchers made multiple corrections to the press that covered the IronPeak blog.[32]
In October 2020, a hardware flaw in the chip's security features was found that might be exploited in a way that cannot be patched, using a similar method as the jailbreaking of the iPhone with A10 chip, since the T2 chip is based on the A10 chip. Apple was notified of this vulnerability but did not respond before security researchers publicly disclosed the vulnerability.[33] It was later demonstrated that this vulnerability can allow users to implement custom Mac startup sounds.[34][35]
^ abcDavidov, Mikhail; Erickson, Jeremy (August 8, 2019). "Inside The Apple T2"(PDF). Black Hat USA 2019. Archived(PDF) from the original on June 14, 2021. Retrieved July 11, 2021.
^ abcParrish, Kevin (July 24, 2018). "Apple's T2 chip may be causing issues in iMac Pro and 2018 MacBook Pros". DigitalTrends. Archived from the original on September 18, 2018. Retrieved January 22, 2019. Of all the error messages uploaded to these threads, there is one detail they seem to share: Bridge OS. This is an embedded operating system used by Apple's stand-alone T2 security chip, which provides the iMac Pro with a secure boot, encrypted storage, live "Hey Siri" commands, and so on.
