Transcript TRP Launch Model in SAL

Measured Boot Model
Jon Millen, Joshua Guttman, John Ramsdell,
Justin Sheehy, Brian Sniffen, Lindsay Spriggs
MITRE
November, 2007
© 2007 The MITRE Corporation. All rights reserved
Boot Analysis
• Context
– Design study for trust research platform
– Use of Trusted Platform Module, domain separation VMM
• Objective
– Verify evidence of proper system initialization
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© 2007 The MITRE Corporation. All rights reserved
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
VMM
TPM: Trusted Platform Module
PCR: Platform Configuration Register
SINIT
CRTM
TPM
BIOS
PCR 0
PCR 17
PCR 18
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© 2007 The MITRE Corporation. All rights reserved
Modeling Idea
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• Each component has a binary "good" state variable
good
0
– 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
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© 2007 The MITRE Corporation. All rights reserved
system = execs || goodness || main || pcr
execs
goodness
exec[CRTM]
xgood
main
pcr
good[ ]
CRTM
BIOS
pc
pcr0_val
protect_control
exec[BIOS]
xgood
cur_pcr
cur_cmd
cur_locality
target_meas
pcr17_val
pcr18_val
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© 2007 The MITRE Corporation. All rights reserved
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]));
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© 2007 The MITRE Corporation. All rights reserved
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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© 2007 The MITRE Corporation. All rights reserved