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XPDDS17: Introduction to Intel SGX and SGX Virtualization - Kai Huang, Intel

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The Linux Foundation

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In era of cloud computing, security is becoming more and more critical for customers. In existing HW/SW architecture hypervisor does not protect tenants against the cloud provider and thus the supplied operating system and hardware. Intel Software Guard Extension (SGX) provides a mechanism that addresses this scenario. It aims at protecting user-level software from attacks from other processes, the operating system, and even physical attackers. Intel SGX makes such protection possible through the use of enclave, which is a protected area in userspace application where the code/data cannot be accessed directly by any software from outside. This presentation intends to give you an introduction of Intel SGX technology, including what it is, how it works, and the existing SW stack to enable SGX for customers, followed by introduction of our work to support SGX virtualization in Xen hypervisor, including the high-level design, current status and future plan.
Published in: Technology

XPDDS17: Introduction to Intel SGX and SGX Virtualization - Kai Huang, Intel

  1. 1. INTEL RESTRICTED SECRET1 SSG System Software Division Introduction to SGX (Software Guard Extensions) and SGX Virtualization Kai Huang, Jun Nakajima (Speaker) July 12, 2017
  2. 2. INTEL RESTRICTED SECRET2 SSG System Software Division Agenda • SGX Introduction • Xen SGX Virtualization Support • Backup
  3. 3. INTEL RESTRICTED SECRET3 SSG System Software Division SGX: Reduce TCB to “HW + Enclave” App App App OS VMM Hardware App OS VMM Hardware Enclave Attack Surface Today Attack Surface with Enclave Enclave: • A protected container in App’s address space (ring 3). • Even privileged SW cannot access enclave directly. • Reduce TCB to “HW + Enclave” è App gets its own capability of protection
  4. 4. INTEL RESTRICTED SECRET4 SSG System Software Division SGX: Prevent Memory Snooping Attacks • Security perimeter is the CPU package boundary • Data and code unencrypted inside CPU package • Data outside CPU package is encrypted and/or integrity checked • External memory reads and bus snooping only see encrypted data CPU MEE12345678 jco3lks937w Snoop Snoop Memory Bus System Memory *MEE: SGX Memory Encryption Engine
  5. 5. INTEL RESTRICTED SECRET5 SSG System Software Division SGX Enclave • Enclave – Trusted Execution Environment embedded in application – Provides confidentiality and/or integrity – With it’s own code/data. – With controlled entry points – Multiple threads supported • EPC (Enclave Page Cache) – Trusted Memory to commit enclave (via page table) – With additional access check – Typically reserved by BIOS as Processor Reserved Memory – Along with EPCM with limited size (ex, 32M, 64M, 128M) • New SGX instructions to manage/access Enclave – ENCLS, ENCLU. OS Enclave APP stack APP code Enclave stack Enclave heap Enclave code Memory EPC Page table mapping EPCM * EPCM (Enclave Page Cache Map) : Used by HW to track EPC status (not-visible to SW)
  6. 6. INTEL RESTRICTED SECRET6 SSG System Software Division Instruction Behavior Changes in Enclave • Invalid Instructions • Behavior Changes – RDTSC, RDTSCP: Only legal when SGX2 is available. – RDRAND, RDSEED, PAUSE: May cause VMEXIT – INVD: #UD in enclave – INT3
  7. 7. INTEL RESTRICTED SECRET7 SSG System Software Division SGX Application Flow 2. Create enclave 3. CallTrusted () 4. Process secrets 5. Return 6. Cont Untrusted part Trusted part (Enclave) Call Bridge1. Define and partition App to untrusted and trusted part. 2. App creates enclave 3. Trusted function is called; 4. Code in enclave process secrets. 5. Trusted function returns. 6. App continues normal execution. 1. Partition SGX App OS, VMM, BIOS, SMM,…
  8. 8. INTEL RESTRICTED SECRET8 SSG System Software Division Agenda • SGX Introduction • Xen SGX Virtualization Support • Backup
  9. 9. INTEL RESTRICTED SECRET9 SSG System Software Division Virtualizing SGX • General Enabling – Pretty Straightforward – Discover SGX and Manage EPC in Hypervisor – Expose part of the host EPC to guest – Size: configurable from user – Base: calculated internally – SGX CPUID/MSR emulation – Setup EPT mapping for guest EPC and host EPC. – ENCLS and ENCLU runs perfectly in non-root mode. • EPC Virtualization Approaches – Static Partitioning – Oversubscription – Ballooning
  10. 10. INTEL RESTRICTED SECRET10 SSG System Software Division SGX Interaction with VMX • New ENCLS VMEXIT – New bit in secondary exec control to enable ENCLS VMEXIT – New 64-bit bitmap to control which ENCLS leaves will trigger VMEXIT • New bits to indicate whether VMEXIT (any) is from Enclave – Bit 27 in exit_reason – Bit 4 in GUEST_INTERRUPTBILITY_INFO.
  11. 11. INTEL RESTRICTED SECRET11 SSG System Software Division Enclave SGX App ACPI/CPUID/MSR EPT mapping Xen SGX App Notify - EPC base - EPC size Enclave Xen SGX Virtualization Support Guest EPC SGX driver * EPT Violation * ENCLS Emulation Dom0 HVM XL Tools memory = 1024 epc = 64M … Kernel EPT Violation handler ENCLS Emulation handler Host EPCEPC Management Exposing EPCPopulate EPC * ENCLS emulation & EPT violation may not needed, depending on implementation of EPC virtualization Hypervisor Changes
  12. 12. INTEL RESTRICTED SECRET12 SSG System Software Division EPC Virtualization Approaches (3) Pros Cons Static Partitioning • Easy implementation (no ENCLS trapping/emulation, No EPT violation) • No hypervisor overhead Potential inefficient use of EPC Ballooning • Pros of “static partitioning” • More efficient use of EPC Require ballooning driver in guest Oversubscription More efficient use of EPC • Complicated implementation • Higher hypervisor overhead • We have preliminary patches on github with “static partitioning” implemented. • Oversubscription vs Ballooning?
  13. 13. INTEL RESTRICTED SECRET13 SSG System Software Division Questions?

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