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The Effectiveness of Instruction Set Randomization

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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  1. 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

  2. Instruction Set Randomization Encryption Key Decryption Key Compile Load In memory Execution

  3. 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

  4. 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

  5. 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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