System Security 论文笔记 CC

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COIN Attack


To find vulnerabilities of SGX applications in four models:

  • Concurrent calls: multithread, race condition, improper lock…
  • Order: assumes the calling sequence
  • Input manipulation: bad OCALL return val & ECALL arguments
  • Nested calls: calling OCALL that invokes ECALL, not implemented

Design & Method

The design of COIN:

COIN Overview

COIN Modules

  • Emulation: QEMU
  • Symbolic execution: Triton (backed by z3)
  • Policy-based vulnerability discovery


COIN uses 8 policies to find the potential vulnerabilities:

  • Heap info leak
  • Stack info leak
  • Ineffectual condition
  • Use after free
  • Double free
  • Stack overflow
  • Heap overflow
  • Null pointer dereference



  • Symbolic execution + emulation
  • Policies can be configurable
  • Real world problems


  • nested call left unimplemented
  • May not be powerful enough to deal with complicate situations
    • Policies are mainly at relatively low-level


  • USENIX Security 2020
  • Paper
  • Source code unavailable

Traditional TrustZone OSes and Applications is not easy to fuzz because they cannot be instrumented or modified easily in the original hardware environment. So to emulate them for fuzzing purpose.


  • Emulate TrustZone OSes(TZOS) and Trusted Applications (TAs)
  • Abstract and reimplement a subset of hardware/software interfaces
  • Fuzz these components
  • TZOSes: QSEE, Huawei, OPTEE, Kinibi, TEEGRIS(Samsung) & TAs

Design & Method


  • Re-host the TZOS frimware
  • Choose the components to reuse/emulate carefully
    • Bootloader
    • Secure Monitor
    • TEE driver and TEE userspace
    • MMIO registers (easy to emulate)


  • TriforceAFL + QEMU
  • Manually written Interfaces


Emulations works well. For upgraded TZOSes, only a few efforts are needed for compatibility.



  • Identifying the fuzzed target
  • Result stability (migrate to hardware, reproducibility)
  • Randomness
Class Vulnerability Types Crashes
Availability Null-pointer dereferences 9
  Insufficient shared memory crashes 10
  Other 8
Confidentiality Read from attacker-controlled pointer to shared memory 8
  Read from attacker-controlled 0
  OOB buffer length to shared memory  
Integrity Write to secure memory using attacker-controlled pointer 11
  Write to secure memory using 2
  attacker-controlled OOB buffer length  

Just like the previous paper, the main causes of the crashes can be attributed to:

  • Assumptions of Normal-World Call Sequence
  • Unvalidated Pointers from Normal World
  • Unvalidated Types


  • Normal-World Checks
  • Assumptions of Normal-World Call Sequence



  • Solid work
  • Efforts taken to run TZOS and TA in emulation environment
  • Acceptable performance


  • Low coverage
  • Crashes -X-> vulnerabilities