Quick introduction to reverse engineering for beginners

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Chapter 8 Other things 8.1 Compiler’s anomalies Intel C++ 10.1, which was used for Oracle RDBMS 11.2 Linux86 compilation, may emit two JZ in row, and there are no references to the second JZ. Second JZ is thus senseless. For example, kdli.o from libserver11.a: .text:08114CF1 loc_8114CF1: ; CODE XREF: __PGOSF539_kdlimemSer+89A .text:08114CF1 ; __PGOSF539_kdlimemSer+3994 .text:08114CF1 8B 45 08 mov eax, [ebp+arg_0] .text:08114CF4 0F B6 50 14 movzx edx, byte ptr [eax+14h] .text:08114CF8 F6 C2 01 test dl, 1 .text:08114CFB 0F 85 17 08 00 00 jnz loc_8115518 .text:08114D01 85 C9 test ecx, ecx .text:08114D03 0F 84 8A 00 00 00 jz loc_8114D93 .text:08114D09 0F 84 09 08 00 00 jz loc_8115518 .text:08114D0F 8B 53 08 mov edx, [ebx+8] .text:08114D12 89 55 FC mov [ebp+var_4], edx .text:08114D15 31 C0 xor eax, eax .text:08114D17 89 45 F4 mov [ebp+var_C], eax .text:08114D1A 50 push eax .text:08114D1B 52 push edx .text:08114D1C E8 03 54 00 00 call len2nbytes .text:08114D21 83 C4 08 add esp, 8 From the same code: .text:0811A2A5 loc_811A2A5: ; CODE XREF: kdliSerLengths+11C .text:0811A2A5 ; kdliSerLengths +1C1 .text:0811A2A5 8B 7D 08 mov edi, [ebp+arg_0] .text:0811A2A8 8B 7F 10 mov edi, [edi+10h] .text:0811A2AB 0F B6 57 14 movzx edx, byte ptr [edi+14h] .text:0811A2AF F6 C2 01 test dl, 1 .text:0811A2B2 75 3E jnz short loc_811A2F2 .text:0811A2B4 83 E0 01 and eax, 1 .text:0811A2B7 74 1F jz short loc_811A2D8 .text:0811A2B9 74 37 jz short loc_811A2F2 .text:0811A2BB 6A 00 push 0 .text:0811A2BD FF 71 08 push dword ptr [ecx+8] 197
.text:0811A2C0 E8 5F FE FF FF call len2nbytes It’s probably code generator bug wasn’t found by tests, because, resulting code is working correctly anyway. 198
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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
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4.2 Middle level 4.2.1 Task 2.1 Wel
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mov [edx+eax], bl mov ebx, edi mov
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loc_80485AB: ; CODE XREF: f+1E0 ; f
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mov [ecx+eax], dl inc eax cmp ebx,
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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 192 and 193: .text:64405171 call dbg .text:64405
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 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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