The effectiveness of instruction set randomization
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Where's the FEEB?: The Effectiveness of Instruction Set Randomization. Nora Sovarel, David Evans, Nate Paul. To appear at USENIX Security, August 2005. The Effectiveness of Instruction Set Randomization. Nora Sovarel http://www.cs.virginia.edu/nora University of Virginia Computer Science

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The Effectiveness of Instruction Set Randomization

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Where's the FEEB?: The Effectiveness of Instruction Set Randomization. Nora Sovarel, David Evans, Nate Paul.To appear at USENIX Security, August 2005

The Effectiveness of Instruction Set Randomization

Nora Sovarel

http://www.cs.virginia.edu/nora

University of Virginia

Computer Science

2005 IEEE Symposium on Security and Privacy


Instruction Set Randomization

Encryption Key

Decryption Key

Compile

Load

In memory

Execution


2-byte instruction

Correct: infinite loop

Wrong:

Usually crashes

Sometimes false positive

False positives

Conditional jumps

Used to reduce the number of attempts (average 24 per byte)

Jump Attack: jmp -2

eb

eb

fe

fe

cd

0xbfffe990

0xbfffe991


Requirements

  • Multiple guess attempts on same key

    • Server forks process

    • No rerandomization

  • Remotely observable behavior

  • Injection at known address

  • Simple encryption scheme

    • Byte-wise

    • Learn key from one plain/cipher pair


Conclusion

  • It sometimes works

  • Possible countermeasures

    • Rerandomize periodically

    • Stronger encryption

http://www.cs.virginia.edu/nora

Where's the FEEB?: The Effectiveness of Instruction Set Randomization. Nora Sovarel, David Evans, Nate Paul. To appear at USENIX Security 2005


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