Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Reverse Engineering automation

995 views

Published on

Published in: Technology
  • Be the first to comment

Reverse Engineering automation

  1. 1. by Anton Dorfman PHDAYS 2014, Moscow
  2. 2.  Fan of & Fun with Assembly language  Researcher  Scientist  Teach Reverse Engineering since 2001  Candidate of technical science  Lecturer at Samara State Technical University and Samara State Aerospace University
  3. 3.  Intro  Simple  Trace & Coverage  Graph  Program Slicing  All Together
  4. 4.  Iterative process  Understand small piece of code – make abstraction in mind  Understand all pieces of code in procedure – unite all abstractions – make abstraction about function  And etc  Good visualization important  Many routine tasks
  5. 5.  Code localization  Data flow dependencies  Code flow dependencies  Local variables checking  Input output procedures parameters checking  Variables range checking  Labels naming  Function naming  Function prototyping
  6. 6.  Biggest science school - Professor Thomas W. Reps - University of Wisconsin-Madison - http://pages.cs.wisc.edu/~reps/  In Russia – Institute for System Programming Russian Academy of Science - http://www.ispras.ru
  7. 7.  Dynamic Binary Instrumentation (DBI)  Intermediate representation (IR)  System emulators
  8. 8.  Function  Variable  Label
  9. 9.  Also called Execution Trace  Trace of program execution  Simpe case - just a list of addresses that instruction pointer takes on single run
  10. 10.  Firstly used as a measure to describe the degree to which the source code of a program is tested by a particular test suite.  List of instructions that executed during single run  List of unique addresses from program trace
  11. 11.  Difference between code coverage can help to locate code that do some functionality  Common code coverage – common functionality  More runs – more diff between code coverage – precise code localization
  12. 12.  The collection of all memory accesses performed by an application in single run  Include both writes and reads
  13. 13.  Include Code Trace  Include all registers values and memory values at every execution point  May be absolute – save all values  Relative – just save values that changed at this execution point
  14. 14.  Directed graph that shows control dependencies between blocks of commands  Each node represents basic block  Basic block – piece of code ends with jump, starts with jump target without any jump or jump target inside block  Two special blocks – entry block and exit block
  15. 15.  Directed graph that represents calling relationships between subroutines in a computer program  Each node represents procedure  Each edge (a, b) indicates that procedure a calls procedure b  Cycle in the graph indicates recursive procedure calls  Static call graph represents every possible run of the program  Dynamic call graph is a record of an execution of the program
  16. 16.  Directed graph that represents data dependencies between a number of operations  Each node represents operation  Each edge represents variable
  17. 17.  Ottenstein & Ottenstein – PDG, 1984  Actually – Procedure dependence graph because introduced for programs with one procedure  Each node represents a statement  Two types of edges  Control Dependence – between a predicate and the statements it controls  Data Dependence – between statements modifying a variable and those that may reference it  Special “Entry” node is connected to all nodes that are not control dependant
  18. 18.  Horowitz, Reps & Binkly – SDG, 1990  PDG included for procedures  New nodes: Call Site, Procedure Entry, Actual-in- argument, Actual-out-argument, Formal-in- parameter, Formal-out-parameter  3 new edge types  Call Edge – connect “call site” and “procedure entry”  Parameter-In Edge – connect “Actual-in” with “Formal-in”  Parameter-Out-Edge – connect “Actual-out” with “Formal-out”
  19. 19.  Large programs must be decomposed for understanding and manipulation.  However, it should be into procedures and abstract data types.  Program Slicing is decomposition based on data flow and control flow analysis.  A study showed, experienced programmers mentally slicing while debugging.  “The mental abstraction people make when they are debugging a program” [Weiser]
  20. 20.  All the statements of a program that may affect the values of some variables in a set V at some point of interest i.  A slicing criterion of a program P is a tuple (i, V), where i is a statement in P and V is a subset of variables in P.  Slicing Criterion: C = (i , V)
  21. 21.  Direction of slicing ◦ Backward ◦ Forward  Slicing techniques ◦ Static ◦ Dynamic ◦ Conditioned  Levels of slices ◦ Intraprocedural slicing ◦ Interprocedural slicing
  22. 22.  Original Slicing Method  Backward slice of a program with respect to a program point i and set of program variables V consists of all statements and predicates in the program that may affect the value of variables in V at I  Answer the question “what program components might effect a selected computation?”  Preserve the meaning of the variable (s) in the slicing criterion for all possible inputs to the program
  23. 23.  Slice criterion <12,i> ◦ 1 main( ) ◦ 2 { ◦ 3 int i, sum; ◦ 4 sum = 0; ◦ 5 i = 1; ◦ 6 while(i <= 10) ◦ 7 { ◦ 8 Sum = sum + 1; ◦ 9 ++ i; ◦ 10 } ◦ 11 Cout<< sum; ◦ 12 Cout<< i; ◦ 13 }
  24. 24. • Forward slice of a program with respect to a program point i and set of program variables V consists of all statements and predicates in the program that may be affected by the value of variables in V at I • Answers the question “what program components might be effected by a selected computation?” • Can show the code affected by a modification to a single statement
  25. 25.  Slice criterion <3,sum> ◦ 1 main( ) ◦ 2 { ◦ 3 int i, sum; ◦ 4 sum = 0; ◦ 5 i = 1; ◦ 6 while(i <= 10) ◦ 7 { ◦ 8 sum = sum + 1; ◦ 9 ++ i; ◦ 10 } ◦ 11 Cout<< sum; ◦ 12 Cout<< i; ◦ 13}
  26. 26.  Static Slicing does not make any assumptions regarding the input.  Slices derived from the source code for all possible input values  May lead to relatively big slices  Contains all statements that may affect a variable for every possible execution  Current static methods can only compute approximations
  27. 27.  Slice criterion (12,i) ◦ 1 main( ) ◦ 2 { ◦ 3 int i, sum; ◦ 4 sum = 0; ◦ 5 i = 1; ◦ 6 while(i <= 10) ◦ 7 { ◦ 8 sum = sum + 1; ◦ 9 ++ i; ◦ 10 } ◦ 11 Cout<< sum; ◦ 12 Cout<< i; ◦ 13 }
  28. 28.  First introduced by Korel and Laski  Dynamic Slicing assumes a fixed input for a program.  Only the dependences that occur in a specific execution of the program are taken into account  Computed on a given input  Dynamic slicing criterion is a triple (input, occurrence of a statement, variable) – it specifies the input, and distinguishes between different occurrences of a statement in the execution history
  29. 29. 1. read (n) 2. for I := 1 to n do 3. a := 2 4. if c1==1 then 5. if c2==1 then 6. a := 4 7. else 8. a := 6 9. z := a 10. write (z) • Assumptions – Input n is 1 – C1, c2 both true – Execution history is 11, 21, 31, 41, 51, 61, 91, 22, 101 – Slice criterion<1, 101, z>
  30. 30.  Assumptions - Input ‘a’ is positive number 1. read(a) 2. if (a < 0) 3. a = -a 4. x = 1/a
  31. 31.  Computes slice within one procedure  Consists basically of two steps:  A single slice of the procedure containing the slicing criterion is made.  Procedure calls from within this procedure are sliced using new criteria.
  32. 32.  Compute slice over an entire program  Two ways for crossing procedure boundary  Up – going from sliced procedure into calling procedure  Down – going from sliced procedure into called procedure  Must Be Context Sensitive
  33. 33.  Chopping  Value Set Analysis
  34. 34.  CodeSurfer ◦ Commercial product by GammaTech Inc. ◦ GUI Based ◦ Scripting language-Tk  Unravel ◦ Static program slicer developed at NIST ◦ Slices ANSI C programs ◦ Limitations are in the treatment of Unions, Forks and pointers to functions
  35. 35.  Slicing of Register on Code Coverage  Graph based view of file reading and moves between memory blocks
  36. 36.  dorfmananton@gmail.com

×