Demystifying the Secure Enclave Processor

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Secure Enclave Processor • Security circuit designed to perform secure services for the rest of the SOC ▫ Prevents main processor from gaining direct access to sensitive data • Used to support a number of different services ▫ Most notably Touch ID • Runs its own operating system (SEPOS) ▫ Includes its own kernel, drivers, services, and applications
Secure (?) Enclave Processor • Very little public information exists on the SEP ▫ Only information provided by Apple • SEP patent only provides a high level overview ▫ Doesn’t describe actual implementation details • Several open questions remain ▫ What services are exposed by the SEP? ▫ How are these services accessed? ▫ What privileges are needed? ▫ How resilient is SEP against attacks?
Page 1 and 2: Demystifying the Secure Enclave Pro
Page 3: Introduction • iPhone 5S was a te
Page 7 and 8: Glossary • AP: Application Proces
Page 11 and 12: Dedicated Hardware Peripherals •
Page 13 and 14: Physical Memory • Dedicated BootR
Page 17 and 18: SEP Initialization - Page Tables
Page 19 and 20: SEP Initialization - Second Stage
Page 21 and 22: SEP Boot Flow SEP AP Configure TZ0
Page 23 and 24: Memory Encryption Setup • Use “
Page 25 and 26: • Mode actually used is AES-256-X
Page 27 and 28: SEP Boot Flow: Stage 3 SEP AP Ackno
Page 29 and 30: Sending SEPOS • SEPOS is sent (op
Page 31 and 32: Boot-loading: Img4 • SEP uses the
Page 33 and 34: Img4 - Manifest • The manifest (A
Page 35 and 36: IMG4 - Manifest Properties (2/2) He
Page 37 and 38: Reversing SEP’s Img4 Parser: Stag
Page 39 and 40: Img4 Parsing Flow SEP AP Decode Pay
Page 43 and 44: Secure Mailbox • Actual mailbox i
Page 45 and 46: Interrupt-based Message Passing •
Page 47 and 48: Mailbox Message Format • A single
Page 49 and 50: SEP Endpoint • Each endpoint is r
Page 51 and 52: SEP Endpoints (2/2) Index Name Driv
Page 53 and 54: Control Endpoint Opcodes Opcode Nam
Page 55 and 56:
Endpoint Registration (AP) Start Cr
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Demystifying the Secure Enclave Pro
Page 59 and 60:
L4-embedded • Modified version of
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SEPOS Architecture SEP Applications
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System Calls (1/2) Num Name Descrip
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Privileged System Calls • Some sy
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SEPOS (INIT) • Initial process on
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Application List • Includes infor
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Bootstrap Server • Implements the
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Privileged Methods • An applicati
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proc_has_privilege( ) int proc_has_
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Entitlement Assignment int proc_cre
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SEP Drivers • Hosts all SEP drive
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Driver Interaction Retrieves SEPD t
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SEP Services • Hosts various SEP
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Service Interaction Retrieves sepS
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Demystifying the Secure Enclave Pro
Page 89 and 90:
Attack Surface: AKF Endpoints • E
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Attack Surface: Endpoint Handler SE
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Address Space Layout - Image • SE
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Stack Corruptions • The main thre
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Stack Corruptions • SEP applicati
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Heap Corruptions: malloc() Free Lis
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No-Execute Protection • SEPOS imp
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Attack Surface: BootROM • Effecti
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Attack Surface: Hardware • Memory
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End Game: JTAG • Glitch the fuse
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Conclusion • SEP(OS) was designed
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Thanks! • Questions?
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SEPOS: System Methods Class Id Meth
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SEPOS: Object Methods (2/2) Class I
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Demystifying the Secure Enclave Processor

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