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Certificate Translation for Specification Preserving Advices Certificate Translation for Specification Preserving Advices Gilles Barthe and Csar Kunz INRIA Sophia Antipolis - Mditerrane FOAL 2008 Csar Kunz (with Gilles Barthe) FOAL

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César Kunz (with Gilles Barthe) Certificate Translation for Specification Preserving Advices FOAL 2008

Certificate Translation for Specification Preserving Advices

FOAL 2008 Gilles Barthe and César Kunz INRIA Sophia Antipolis - Méditerranée

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César Kunz (with Gilles Barthe) Certificate Translation for Specification Preserving Advices FOAL 2008

MOTIVATION SPECIFICATION PRESERVING ADVICES PROVING SPECIFICATION PRESERVING ADVICES REDUCING PROOF OBLIGATIONS IMPROVING THE VERIFICATION POWER CERTIFICATE TRANSLATION

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Local reasoning on:

  • Baseline Code (to understand main functionality)
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Local reasoning on:

  • Baseline Code (to understand main functionality)
  • Advice Code

(to understand the implemented aspect Incremental concerns:

  • Contract enforcement
  • Logging / Profiling
  • Evolving Security Requirements
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Local reasoning on:

  • Baseline Code (to understand main functionality)
  • Advice Code

(to understand the implemented aspect Global analysis of pointcuts to understand interaction of aspects Incremental concerns:

  • Contract enforcement
  • Logging / Profiling
  • Evolving Security Requirements
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Dantas & Walker [POPL06]:

  • characterize Harmless Advices that

allow local reasoning

  • information flow analysis to check

advice non-interference.

Producer vs Consumer Perspective

Obliviousness -> Local Reasoning? Syntactic Obliviousness vs. Semantic Obliviousness Syntactic Obliviousness is not enough baseline code Satisfies contract P Advice code baseline code Satisfies contract P

  • functional properties (logic formulae)
  • Absence of null pointer access
  • Type Safety, etc.

PCC setting: contract enforcement Contract preserv. vs semantic preserv weaker requirement

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MOTIVATION SPECIFICATION PRESERVING ADVICES PROVING SPECIFICATION PRESERVING ADVICES REDUCING PROOF OBLIGATIONS IMPROVING THE VERIFICATION POWER CERTIFICATE TRANSLATION

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Strong specification Harmless

  • Spec. preserving

NO NO

Specification Preserving Advices

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Harmless

  • Spec. preserving

NO YES

Specification Preserving Advices

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Harmless

  • Spec. preserving

YES NO

Specification Preserving Advices

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A specification preserving advice may modify variables in the specification.

  • Output value may differ
  • is not invalidated.
  • is ensured.

Harmless

  • Spec. preserving

NO YES

Specification Preserving Advices

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MOTIVATION SPECIFICATION PRESERVING ADVICES PROVING SPECIFICATION PRESERVING ADVICES REDUCING PROOF OBLIGATIONS IMPROVING THE VERIFICATION POWER CERTIFICATE TRANSLATION

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Proving spec-preservation

f f Verification of spec. preservation: wp-based Vcgen over modified advice code. Baseline Code Verification: wp-based Vcgen

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f f

Proving spec-preservation

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MOTIVATION SPECIFICATION PRESERVING ADVICES PROVING SPECIFICATION PRESERVING ADVICES REDUCING PROOF OBLIGATIONS IMPROVING THE VERIFICATION POWER CERTIFICATE TRANSLATION

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Specification Harmless Advices

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Specification Harmless Advices

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Specification Harmless Advices

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Does not modify V and res=x Does not modify V

Specification Harmless Advices

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Does not modify V and res=x Does not modify V

Specification Harmless Advices

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Does not modify V and res=x Does not modify V Does not modify V and res=x Does not modify V

Specification Harmless Advices

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Does not modify V and res=x Does not modify V Does not modify V and res=x Does not modify V

Specification Harmless Advices

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MOTIVATION SPECIFICATION PRESERVING ADVICES PROVING SPECIFICATION PRESERVING ADVICES REDUCING PROOF OBLIGATIONS IMPROVING THE VERIFICATION POWER CERTIFICATE TRANSLATION

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f f

IMPROVING THE VERIFICATION POWER

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f f g g

IMPROVING THE VERIFICATION POWER

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Drawback Multiple advised procedures = multiple verification invariants. f f g g Or you want to verify the advice locally without considering for the moment in which contexts it will be executed!

IMPROVING THE VERIFICATION POWER

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Drawback (specification of proceed improves modularity) Multiple advised procedures = multiple verification invariants. f f g g Or you want to verify the advice locally without considering for the moment in which contexts it will be executed!

IMPROVING THE VERIFICATION POWER

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Some advices are be spec-preserving when combined but not when analyzed in isolation ... ... ... Interference is not always a bad thing.

IMPROVING THE VERIFICATION POWER

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Baseline proc.

...

IMPROVING THE VERIFICATION POWER

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Baseline proc. Baseline proc.

...

IMPROVING THE VERIFICATION POWER

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Baseline proc. Baseline proc.

...

IMPROVING THE VERIFICATION POWER

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Baseline proc. Baseline proc.

...

IMPROVING THE VERIFICATION POWER

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Baseline proc.

. . .

... Baseline proc.

...

IMPROVING THE VERIFICATION POWER

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Baseline proc.

. . .

... Baseline proc.

...

IMPROVING THE VERIFICATION POWER

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Specification Refinement instead of Specification Preservation Baseline proc.

. . .

...

IMPROVING THE VERIFICATION POWER

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MOTIVATION SPECIFICATION PRESERVING ADVICES PROVING SPECIFICATION PRESERVING ADVICES REDUCING PROOF OBLIGATIONS IMPROVING THE VERIFICATION POWER CERTIFICATE TRANSLATION

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Certificate Translation

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. . . . . . Execution OK Code Certificate Code Certificate Code Certificate Baseline Code Producer Advice Code Producer Advice Code Producer Producer Side Consumer Side Consider the situation:

  • Client verification and execution environment not AOP-oriented
  • Code generated by multiple producers is weaved before execution

Proof Checker Weaved Code Code Weaving

Certificate Translation

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. . . Code Certificate Code Certificate Code Certificate . . . Weaved Code Execution Proof Checker OK Baseline Code Producer Advice Code Producer Advice Code Producer Producer Side Consumer Side Code Weaving

Certificate Translation

Certificate Consider the situation:

  • Client verification and execution environment not AOP-oriented
  • Code generated by multiple producers is weaved before execution

Certificate Translation

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Baseline Source Code

Compiler

Low level Code

Certificate Translation

High level/structured Low level/stack based

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Baseline Source Code

Certificate Translation

Certificate

Compiler

Low level Code Certificate

Certificate Translation

High level/structured Low level/stack based

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Baseline Source Code Advice Source Code Final Weaved Code

Certificate Translation

Certificate

Compiler

Low level Code Certificate

Compiler + Weaving

Certificate Translation

High level/structured Low level/stack based

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Baseline Source Code Advice Source Code Final Weaved Code

Certificate Translation

Certificate

Compiler

Low level Code Certificate

  • Cert. Trans.

for adv. weaving Compiler + Weaving

Certificate

  • preserv.

Certificate

Certificate Translation

High level/structured Low level/stack based

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Conclusions

  • A more flexible notion of non-interfering advices
  • Stronger non-interference analyses reduce proof obligations
  • Certificate translation targetting a typical backend