Software Verification Contracts, Trusted Components and Patterns
description
Transcript of Software Verification Contracts, Trusted Components and Patterns
Chair of Software Engineering
Software VerificationContracts, Trusted Components
and Patterns
Bertrand MeyerManuel Oriol
Till BayETH, Fall 2008
Chair of Software Engineering
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Today & next lecture
Aims of the courseIntroduction to issues of software qualityAxiomatic semantics and program correctness (1)
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Aims of this course
To provide a survey of
Reuse and component technology, with a special emphasis on object-oriented approaches
Techniques for quality components
Software verification techniques
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Topics Quality issues in software engineering Components and the notion of trusted component Designing O-O libraries Axiomatic Semantics and Program Correctness Componentization: turning patterns into
Components Automatic component testing techniques Program analysis Model checking Abstract interpretation Separation logic (guest lectures by Cristiano
Calcagno) Proof-Carrying Code
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Basic references
Clemens Szyperski, Component Software, Addison-Wesley, 1998Bertrand Meyer, Object-Oriented Software Construction, 2nd edition, Prentice Hall, 1997Bertrand Meyer, Reusable Software, Prentice Hall, 1994Martin Abadi, Luca Cardelli: A Theory of Objects, Springer-Verlag, 1996Robert V. Binder: Testing Object-Oriented Systems: Models, Patterns, and Tools, Addison-Wesley, 1999. Karine Arnout: From Patterns to Components, ETH Ph.D. thesis, 2004Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides: Design Patterns: Elements of Reusable Object-Oriented Software, Addison-Wesley, 1995
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OrganizationCourse page
http://se.ethz.ch/teaching/2008-F/tc-0239/index.htmlLectures:
Monday: 2 hoursWednesday: 1 hour -- exercises and applications
Assistant: Stephan van Staden [email protected]
All exercises are optional, but will be corrected. They are an important preparation for the exam and the project.
Grading:Written exam on date of 15 December (lecture time):
70%Project (take-home exercise): 30%
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Reading assignment“Ariane” paper: http://tinyurl.com/xy3sAlso read Ken Garlington’s criticism (link in the article) (and optionally) the official report on the Ariane crash
Chapter 9 of “Introduction to the Theory of Programming Languages”
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PART 1: Introduction
Issues of Software Quality
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Software quality: external vs internal External factors: visible to customers
(not just end users but e.g. purchasers)
Examples: ease of use, extendibility, timeliness
Internal factors: perceptible only to developers
Examples: good programming style, information hiding
Only external factors count in the end, but the internal factors make it possible to obtain them.
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Software quality: product vs process
Product: properties of the resulting software
For example: correctness, efficiency
Process: properties of the procedures used to produce and “maintain” the software
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External quality factors
CorrectnessRobustnessSecurityEase of useEase of learningEfficiency
ExtendibilityReusabilityPortability
TimelinessCost-effectiveness
Security
Hostility
Robustness
Errors
Correctness
Specification
Process quality:
Product quality (long-term):
Product quality (immediate):
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Reliability
Correctness:The systems’ ability to perform according to specification, in cases covered by the specification
Robustness:The systems’ ability to perform reasonably in cases not covered by the specification
Security (integrity):The systems’ ability to protect itself against hostile use
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Ariane 5, 1996
$500 million, not insured.40 seconds into flight, exception in Ada program not processed; order given to abort the mission.Exception was caused by an incorrect conversion: a 64-bit real value was incorrectly translated into a 16-bit integer.• Not a design error.• Not an implementation error.• Not a language issue.• Not really a testing problem.• Only partly a quality assurance issue.Systematic analysis had “proved” that the exception could not occur – the 64-bit value (“horizontal bias” of the flight) was proved to be always representable as a 16-bit integer !
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Ariane-5 (Continued)It was a REUSE error:• The analysis was correct – for Ariane 4 !• The assumption was documented – in a design document !With assertions, the error would almost certainly (if not avoided in the first place) detected by either static inspection or testing:
integer_bias (b: REAL): INTEGER is require representable (b) do … ensure equivalent (b, Result) end
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NIST report on “testing” (2002)
Monetary effect onDevelopers andUser due to“insufficient testing infrastructure”:
$59.5 billion
(Financial sector: $3.3 billion,auto/aerospace $1.8 billion etc.)
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From reliability to security
Buffer overflow(Morris worm, most viruses)
See http://www.cert.org
Some_innocuous_public_command “Some message”(Or maybe just inputting text into a browser field)
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Buffer overflow
Memory Setup
0 Max
Program Heap Stack
Stack frames
MainRout1Routn
Stack growth …
Stack top Stack bottom
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Calling a routine
0 Max
Program Heap Stack
Stack frames
MainRout1Routn…Args
ofRout
Localsof
Rout
Return address
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Calling a utility
syslogd "Some error message“
finger Some_name
some_command "some text"
(Text input into some browser field)
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Allocating the buffer
0 Max
Program Heap Stack
Stack frames
MainRout1Routn…Args
ofRout
Return address
Other locals
Buffer
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How was the routine coded?from i := 1 until
i > input_sizeloop
buffer [i] := input [i]i := i + 1
end
from i := 1 untili > input_size or i > buffer_size
loopbuffer [i] := input [i]i := i + 1
end
(1)
(2)
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Allocating the buffer
0 Max
Program Heap Stack
Stack frames
MainRout1Routn…Args
ofRout
Return address
Other locals
Buffer
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Getting close
0 Max
Program Heap Stack
Stack frames
MainRout1Routn…
Return address
Other locals
Buffer
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Getting closer
0 Max
Program Heap Stack
Stack frames
MainRout1Routn…
Return address
Other locals
Buffer
Available !
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Inserting the code
0 Max
Program Heap Stack
Stack frames
MainRout1Routn…
Return address
Other locals
Buffer
Available !
Your Code
Modified Return Address
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Buffer overflow: lessons
Lack of specificationLack of specification enforcementProgramming techniquesSecurity concepts
At the core, a programming methodology issue
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Software quality (through technology)
A priori (build it right)Object technology, formal development
A posteriori (validate and fix it)Testing, abstract interpretation, model
checking
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Management aspects
Process standards: CMMI, ISO 9001Get software in source from, benefit from public scrutinyMetrics collection and applicationCode reviews?
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Today’s software is often good enough
Overall:Works most of the timeDoesn’t kill too many peopleNegative effects, esp. financial, are diffuse
Significant improvements since early years:Better languagesBetter toolsBetter practices (configuration management)
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From “good enough” to good?
Beyond “good enough”, quality is economically badHe who perfects, dies
Actual
IdealQuality
1 2 3
Time4
Choose to release?
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The economic argument
Stable system: Sum of individual optima = Global optimum
Non-component-based development: Individual optimum = “Good Enough Software” Improvements: I am responsible!
Component-based development: Interest of both consumer and producer: Better
components Improvements: Producer does the job
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Quality through reuse
The good news:
Reuse scales up everything
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Quality through reuse
The good news:
Reuse scales up everything
The bad news:
Reuse scales up everything
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Trusted components
Confluence of
Quality engineeringReuse
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Classifying components by...
Lifecycle role:• Analysis• Design• Implementation
Flexibility:• Static• Dynamic• Replaceable
Form of use:• Interface only• Source only• Source + hiding
Economics:• Free• Purchased• Rented
Abstraction level:• Functional (subroutine)• Casual (package)• Data (class)• Cluster (framework)• System (binary comp.)
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This is a broad view of components
Encompasses patterns and frameworks
Software, especially with object technology, permits “pluggable” components (“don’t call us, we’ll call you”), where client programmers can insert their own mechanisms.
Supports component families