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Measured Boot Model

Measured Boot Model. Jon Millen, Joshua Guttman, John Ramsdell, Justin Sheehy, Brian Sniffen, Lindsay Spriggs MITRE November, 2007. Boot Analysis. Context Design study for trust research platform Use of Trusted Platform Module, domain separation VMM Objective

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Measured Boot Model

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  1. Measured Boot Model Jon Millen, Joshua Guttman, John Ramsdell, Justin Sheehy, Brian Sniffen, Lindsay Spriggs MITRE November, 2007

  2. Boot Analysis • Context • Design study for trust research platform • Use of Trusted Platform Module, domain separation VMM • Objective • Verify evidence of proper system initialization

  3. Chain of Trust • The TPM (standard v. 1.2) has Platform Configuration Registers • Each component may measure the next (SHA-1 hash) • Signed "TPM quote" reports PCR contents launch sequence VMM TPM: Trusted Platform Module PCR: Platform Configuration Register SINIT CRTM BIOS TPM PCR 0 PCR 17 PCR 18

  4. Modeling Idea 1 good • Each component has a binary "good" state variable • iff it has an expected (symbolic) measurement hash • A "good" component behaves as expected for • measurement of target component into PCR • transfer of control to next component ("program counter" update) • A "not-good" component is unpredictable (non-deterministic) • It could be malicious and falsify measurements! • TPM properties limit consequences of misbehavior • Extend and Reset operations have access control 0

  5. system = execs || goodness || main || pcr execs goodness main pcr cur_pcr cur_cmd cur_locality target_meas exec[CRTM] good[ ] CRTM xgood pc pcr0_val BIOS protect_control exec[BIOS] xgood pcr17_val pcr18_val

  6. Specifications • The main objective is to show that enough good measurements imply that the measured components are good. • Example spec, for VMM: spec: CLAIM system |- G(pcr17_val = SINITm AND pcr18_val = VMMm AND pc = VMM => G(good[VMM]));

  7. Model Checking Experience • Started with SMV • Tried SAL for language benefits (types, arrays) • As models got bigger, SAL model ran much faster than SMV • Specs take from a few seconds to a few minutes to verify • Some style adjustments were needed

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