Quick introduction to reverse engineering for beginners

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.text:64405171 call dbg .text:64405176 add esp, 0Ch ... or: .text:6440237A push eax .text:6440237B push offset aCclientStart_6 ; "CClient::Start: set shortcut user to ’\%"... .text:64402380 push dword ptr [edi+4] .text:64402383 call dbg .text:64402388 add esp, 0Ch It’s very useful. So let’s see contents of that nagging pop-up window function: .text:64404F4F CDwsGui__PrepareInfoWindow proc near .text:64404F4F .text:64404F4F pvParam = byte ptr -3Ch .text:64404F4F var_38 = dword ptr -38h .text:64404F4F var_34 = dword ptr -34h .text:64404F4F rc = tagRECT ptr -2Ch .text:64404F4F cy = dword ptr -1Ch .text:64404F4F h = dword ptr -18h .text:64404F4F var_14 = dword ptr -14h .text:64404F4F var_10 = dword ptr -10h .text:64404F4F var_4 = dword ptr -4 .text:64404F4F .text:64404F4F push 30h .text:64404F51 mov eax, offset loc_64438E00 .text:64404F56 call __EH_prolog3 .text:64404F5B mov esi, ecx ; ECX is pointer to object .text:64404F5D xor ebx, ebx .text:64404F5F lea ecx, [ebp+var_14] .text:64404F62 mov [ebp+var_10], ebx ; demangled name: ATL::CStringT(void) .text:64404F65 call ds:mfc90_316 .text:64404F6B mov [ebp+var_4], ebx .text:64404F6E lea edi, [esi+2854h] .text:64404F74 push offset aEnvironmentInf ; "Environment information:\ n" .text:64404F79 mov ecx, edi ; demangled name: ATL::CStringT::operator=(char const *) .text:64404F7B call ds:mfc90_820 .text:64404F81 cmp [esi+38h], ebx .text:64404F84 mov ebx, ds:mfc90_2539 .text:64404F8A jbe short loc_64404FA9 .text:64404F8C push dword ptr [esi+34h] .text:64404F8F lea eax, [ebp+var_14] .text:64404F92 push offset aWorkingDirecto ; "working directory: ’\%s’\ n" .text:64404F97 push eax ; demangled name: ATL::CStringT::Format(char const *,...) .text:64404F98 call ebx ; mfc90_2539 187
.text:64404F9A add esp, 0Ch .text:64404F9D lea eax, [ebp+var_14] .text:64404FA0 push eax .text:64404FA1 mov ecx, edi ; demangled name: ATL::CStringT::operator+=(class ATL::CSimpleStringT const &) .text:64404FA3 call ds:mfc90_941 .text:64404FA9 .text:64404FA9 loc_64404FA9: .text:64404FA9 mov eax, [esi+38h] .text:64404FAC test eax, eax .text:64404FAE jbe short loc_64404FD3 .text:64404FB0 push eax .text:64404FB1 lea eax, [ebp+var_14] .text:64404FB4 push offset aTraceLevelDAct ; "trace level \%d activated \n" .text:64404FB9 push eax ; demangled name: ATL::CStringT::Format(char const *,...) .text:64404FBA call ebx ; mfc90_2539 .text:64404FBC add esp, 0Ch .text:64404FBF lea eax, [ebp+var_14] .text:64404FC2 push eax .text:64404FC3 mov ecx, edi ; demangled name: ATL::CStringT::operator+=(class ATL::CSimpleStringT const &) .text:64404FC5 call ds:mfc90_941 .text:64404FCB xor ebx, ebx .text:64404FCD inc ebx .text:64404FCE mov [ebp+var_10], ebx .text:64404FD1 jmp short loc_64404FD6 .text:64404FD3 ; --------------------------------------------------------------------------- .text:64404FD3 .text:64404FD3 loc_64404FD3: .text:64404FD3 xor ebx, ebx .text:64404FD5 inc ebx .text:64404FD6 .text:64404FD6 loc_64404FD6: .text:64404FD6 cmp [esi+38h], ebx .text:64404FD9 jbe short loc_64404FF1 .text:64404FDB cmp dword ptr [esi+2978h], 0 .text:64404FE2 jz short loc_64404FF1 .text:64404FE4 push offset aHexdumpInTrace ; "hexdump in trace activated\n" .text:64404FE9 mov ecx, edi ; demangled name: ATL::CStringT::operator+=(char const *) .text:64404FEB call ds:mfc90_945 .text:64404FF1 .text:64404FF1 loc_64404FF1: .text:64404FF1 .text:64404FF1 cmp byte ptr [esi+78h], 0 .text:64404FF5 jz short loc_64405007 188
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Quick introduction to reverse engin
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1.16 C++ classes . . . . . . . . .
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Preface Here (will be) some of my n
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1.1 Hello, world! Let’s start wit
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1.2 Stack Stack — is one of the m
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(_snprintf() function works just li
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1.3 printf() with several arguments
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1.4 scanf() Now let’s use scanf()
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GCC replaced first printf() call to
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}; return 0; printf ("What you ente
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1.5 Passing arguments via stack Now
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1.6 One more word about results ret
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push OFFSET $SG741 ; ’a
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1.8 switch()/case/default 1.8.1 Few
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1.8.2 A lot of cases If switch() st
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loc_804840C: ; DATA XREF: .rodata:0
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et 0 _main ENDP Nothing very specia
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add esp, 1Ch xor eax, eax ; return
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C/C++ standard defines char type as
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eax=eax+ecx return eax ... and this
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mov eax, ecx imul edx sar edx, 1 mo
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; current stack state: ST(0) = resu
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; in local stack here 8 bytes still
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fld QWORD PTR _a$[esp-4] ; current
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In other words, fnstsw ax / sahf in
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1.13 Arrays Array is just a set of
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mov [esp+70h+var_70], eax call _pri
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jge SHORT $LN1@main mov ecx, DWORD
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ebp 0x15 0x15 esi 0x0 0 edi 0x0 0 e
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1.14 Bit fields A lot of functions
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So, let’s download Linux Kernel 2
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There are some redundant code prese
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y 10 just by dropping last digit (3
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_key$ = 8 ; size = 4 _len$ = 12 ; s
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1.15 Structures It can be defined t
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call DWORD PTR __imp__GetSystemTime
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1.15.4 Fields packing in structure
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}; int b; struct outer_struct { cha
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}; printf ("stepping=%d\n", tmp->st
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call ___printf_chk mov eax, esi shr
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mov edx, DWORD PTR _t$[ebp] or edx,
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1.16 C++ classes I placed a C++ cla
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push ecx mov DWORD PTR _this$[ebp],
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call _ZN1c4dumpEv lea eax, [esp+20h
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1.17 Unions 1.17.1 Pseudo-random nu
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xor eax, eax pop esi mov esp, ebp p
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Let’s compile it in MSVC 2010 (I
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comp() function: public comp comp p
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Some compilers can do vectorization
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mov ecx, [esp+10h+var_10] mov edx,
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GCC In all other cases, non-SSE2 co
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add ebx, edx lea esi, [esi+0] loc_8
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movdqa xmm1, XMMWORD PTR [ecx+16] a
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1.20 x86-64 It’s a 64-bit extensi
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} x40 = a3 | x31; x41 = x24 & ~x37;
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or ebx, DWORD PTR _x6$[esp+36] mov
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and r11, r8 and rsi, r8 and r10, r1
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pop rdi pop rsi ret 0 s1 ENDP Nothi
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2.1 LEA instruction LEA (Load Effec
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2.3 npad It’s an assembler macro
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2.4 Signed number representations T
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call function function: .. do somet
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3.2 String Debugging messages are o
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.text:3011E91B DD 1E fstp qword ptr
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loc_80483F2: pop ebp retn _f endp 4
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loc_8048444: loc_8048448: loc_80484
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public f2 f2 proc near push ebp mov
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loc_804840A: loc_804842E: loc_80484
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mov esi, DWORD PTR _k$[esp+16] push
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or eax, edx retn f endp 4.1.8 Task
Page 142 and 143: 4.2 Middle level 4.2.1 Task 2.1 Wel
Page 144 and 145: mov [edx+eax], bl mov ebx, edi mov
Page 146 and 147: loc_80485AB: ; CODE XREF: f+1E0 ; f
Page 148 and 149: mov [ecx+eax], dl inc eax cmp ebx,
Page 150 and 151: Chapter 5 Tools ∙ IDA as disassem
Page 152 and 153: Chapter 7 More examples 147
Page 154 and 155: .text:00541050 arg_0 = dword ptr 4
Page 156 and 157: .text:005410F3 .text:005410F3 loc_5
Page 158 and 159: .text:005411A9 pop ebx .text:005411
Page 160 and 161: .text:00541249 .text:00541249 next_
Page 162 and 163: .text:005412FC mov esi, offset cube
Page 164 and 165: .text:005413DC call _fwrite ; write
Page 166 and 167: .text:005414A7 push ecx ; Filename
Page 168 and 169: .text:005413A3 mov ecx, [esp+44h+pa
Page 170 and 171: .text:00541408 push offset aRb ; "r
Page 172 and 173: }; }; return; fseek (f, 0, SEEK_END
Page 174 and 175: .text:005411B5 mov ebp, eax Check f
Page 176 and 177: .text:0054124C inc ebp .text:005412
Page 178 and 179: This instruction clears bit, in oth
Page 180 and 181: .text:005410CD add esp, 40h .text:0
Page 182 and 183: }; for (i=0; i
Page 184 and 185: }; tmp[y][z]=get_bit (row, y, z); f
Page 186 and 187: }; fread (buf, flen, 1, f); fclose
Page 188 and 189: 7.2 SAP client network traffic comp
Page 190 and 191: .text:64413F68 .text:64413F68 loc_6
Page 194 and 195: .text:64404FF7 push offset aLogging
Page 196 and 197: .text:64405113 loc_64405113: .text:
Page 198 and 199: Now let’s dig deeper and find con
Page 200 and 201: .text:64411E0B .text:64411E0B loc_6
Page 202 and 203: Chapter 8 Other things 8.1 Compiler
Page 204 and 205: Chapter 9 Tasks solutions 9.1 Easy
Page 206 and 207: 9.1.5 Task 1.5 Hint #1: Keep in min
Page 208 and 209: } 9.1.8 Task 1.8 Solution: two 100*
Page 210 and 211: #define PUSH(low, high) ((void) ((t
Page 212 and 213: } } ignore one or both. Otherwise,
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