🤟🏻 🌴 ♨️ OllyDbg on death - saving the workings of the debug session 🦖 🏢 🐑

If you use OllyDbg not for debugging your own applications for which you have debugging information, but for reverse engineering or third-party research, your typical activity is delving into the machine code of someone else's product, understanding the essence of things that are happening and placing a large number of labels (labels ) and comments throughout the code, as well as data sections. You systematically scout the essence of procedures / functions and variables and give them names that reflect your understanding of their purpose.

OllyDbg needs no introduction for everyone involved in debugging, reverse engineering applications, researching or circumventing security mechanisms, etc. It is one of the best user-mode debuggers for Windows, although there are many shortcomings and shortcomings in it that cannot be hushed up.

And now, after a few hours (or even days) of work, when you figured out and signed hundreds, or even thousands of procedures and variables, OllyDbgsuddenly freezes or crashes, taking away all your work (which may include not only labels and comments in large numbers, but also breakpoints and modifications placed in the right places). This is a waste of time and a monstrously demotivating factor, from which one gives up and turns pale.

This article is about how I used OllyDbg in such an emergency to quickly reverse-engineer OllyDbg (partially), save the data hanging by a thread and develop a recipe for actions in case of such disasters.

Since you have continued reading the article, let's agree on some things from the very beginning:

OllyDbg 1.xx, OllyDbg 2.xx, , - , 1.xx ( ).
OllyDbg , , , .. « » — « », , , , OllyDbg. , , — .
IDA Pro , OllyDbg . Audi « BMW» . — , .
, . « » . howto- , SSH, , , , ? , « BSOD» — , , . ?

«» , , , , , . :

(Labels) — OllyDbg , , .
(Comments) — .
(Breakpoints) — .
(Hints) — OllyDbg, , 4 4 , DWORD.

, , , . , , . , , , — - .

, , , , { → } OllyDbg names. .

names PDK

NM_LABEL — User-defined label
NM_EXPORT — Exported (global) name
NM_IMPORT — Imported name
NM_LIBRARY — Name extracted from library, object file or debug data
NM_CONST — User-defined constant (currently not implemented)
NM_COMMENT — User-defined comment
NM_LIBCOMM — Automatically generated comment from library or object file
NM_BREAK — Condition related with breakpoint
NM_ARG — Arguments decoded by analyser
NM_ANALYSE — Comment added by analyser
NM_BREAKEXPR — Expression related with breakpoint
NM_BREAKEXPL — Explanation related with breakpoint
NM_ASSUME — Assume function with known arguments
NM_STRUCT — Code structure decoded by analyzer
NM_CASE — Case description decoded by analyzer
NM_PLUGCMD — Plugin commands to execute at breakpoint
NM_INSPECT — Several last entered inspect expressions
NM_WATCH — Watch expressions

( .udd), — . , - , , , ( ) . , , UDD-, supercool.dll, foo.exe, bar.exe, supercool.dll.

, , OllyDbg ( ). OllyDbg , .

, UDD-? -, , UDD- , . UDD . «Save everything to UDD». «Update .udd file now» — (EXE/DLL/OCX) . , Modules , - . , UDD, . 20 - , UDD , . -, .

4 :

— . BSOD . .
— . , , , , « » « ». ( ?), . . , OllyDbg, , - , .
. OllyDbg . , OllyDbg.exe, . : , OllyDbg «» 27 . , . , OllyDbg, deadlock - Windows, - ( - ). , Microsoft- Spy++, « » , Spy++ GUI- DLL, . - , GUI-. , , . .
OllyDbg UDD-, . UDD- , OllyDbg . , . OllyDbg , , — , , UDD-, . , - . , OllyDbg UDD, UDD-. , UDD- , , , , . — DLL. OllyDbg «» UDD-, , UDD-, , UDD-. UDD-.

, , , , , , , (.. — ).

UDD — . , , . , . .

UDD :

. , git ( ) ( , ). diff , (, custom diff git). , merge — .
, , . , UDD .

- , . - , , . - ( — , , , , , , ..) - - .

- VCS Git , . : ( WinMain()

), — ( , ). , , . , ( memcpy

, strncat

, qsort

). , , (merge conflict), , . « », .

, - - , , , « », , « », . , , - , , ( , new

).

, - ( ) , , , , .

« »

, , , DAW . : - 5—6 , , , , , . merge, , , — VST- , — - . , , , , git diff

, VST- VST- -.

UDD- - , , OllyDbg, ( ( , ) ) ( ), .

Markup Dumper plugin

Markup Dumper, markup — , . «», — markup, , , .

, ,

OllyDbg, , , . , - . , , - .

@ MODULE OLLYDBG
@ VERSION 1.0.10.0
@ BASEADDR 00400000
@ CHECKSUM 17ca77a5

//
// Section: .text
//

LABEL 0040c214 like_ParseStuff
  CMT 0040c4c5 colon case
  CMT 0040c521 eq case
  CMT 0040c575 checking for 1-byte typespec
  CMT 0040c578 jump if more than 2 byte spec
  CMT 00463f08 checking arg1 (addr) against 0
  CMT 00463f0c EDI = arg2 (type of name)
  CMT 00463f0f goto error if addr==NULL
  CMT 00463f11 checking [addr] against 0
  CMT 00463f15 goto error if 0
...
LABEL 004642fb Insertname_EPILOGUE
LABEL 004a3530 like_memcpy
LABEL 004a36d4 like_strlen
LABEL 004a38bc parse_keyword_1
LABEL 004a6c2c like_sprintf

//
// Section: .data
//

LABEL 004eae14 pNamesBlock
LABEL 004eae18 cNameEntriesCur
LABEL 004eae1c cNameEntriesMax
LABEL 004eae30 pNamesStringPool
LABEL 004eae34 cbStringPoolUsed
LABEL 004eae38 cbStringPoolTotal
LABEL 004eae3c xxxWtfNameStringPoolrelated

. , .

, CMT

, LABEL

— . . , git diff , , — , . LABEL

, CMT

, , , git diff , ( ), - , :

, , , , (git add --patch

).

, ( ) , , , - .

, , DVCS , №1 (BSOD ) №4 ( UDD).

№2 №3 ( ). .

, « », « », «», — SEH-, , , « » ( SEH- EXCEPTION_NONCONTINUABLE

).

OllyDbg ( ) — EXCEPTION_ACCESS_VIOLATION

(0xc0000005

), . , EIP , ESP/EBP , . , ( ) . , - . « » , (GetMessage→TranslateMessage→DispatchMessage), , . OllyDbg GUI-, , , .

, - , . EBP . , ( ) , retn

(EIP) .

, , , — () . EXCEPTION_ACCESS_VIOLATION

, ( ). , , , , , DEP, . , ( DEP ), ( , ) , . , , , EIP , , ( , ). , — .

, , , , Markup Dumper, message loop ( ) .

( ), OllyDbg , ( , ), .

, , , EIP , . , OllyDbg , , ( ). , . . , : , , - .

, - , . , , , , , .

Findname()

Findnextname()

— API-, OllyDbg .

void DumpMarkupEx(FILE * fiOutput, int iNameType, char* pszNameType, ulong vaStart, ulong vaLimit)
{
    ulong vaCur;
    char rgchName[TEXTLEN];
    Findname(vaStart-1, iNameType, NULL);
    while(vaCur = Findnextname(rgchName) && vaCur<vaLimit)
        if(vaCur >= vaStart) fprintf(fiOutput, "%5s %.8x %s\n", pszNameType, vaCur, rgchName);
}

void DumpMarkup(FILE * fiOutput, ulong vaStart, ulong vaLimit)
{
    DumpMarkupEx(fiOutput, NM_LABEL, "LABEL", vaStart, vaLimit
    DumpMarkupEx(fiOutput, NM_COMMENT, "CMT", vaStart, vaLimit)
}

: TEXTLEN , , API- Findnextname()

rgchName

. .

, OllyDbg. , — /, .

, , , OllyDbg. , , OllyDbg - (, OllyDbg) .

, - . , - . ( ), (unwinding) , message loop. , Markup Dumper, , , - — EIP , , — , , , , .

10—20% OllyDbg . 80—90% , OllyDbg - WinAPI-, , , . , , - NtWaitForSingleObject, . wait-, - , . Windows deadlock, . , .

, OllyDbg , . , ( New origin here EIP). New Origin Here, EIP — WinAPI- SetThreadContext()

. , Windows , — . APC. «» APC.

, OllyDbg

, Windows, OllyDbg, , , deadlock- , , UI , , (WaitForDebugEvent

, ReadProcessMemory

, WriteProcessMemory

) — . , watchdog-, GUI- ( ) . , Spy++ , .

, , OllyDbg , . OllyDbg — , , , . , TLS , , , , , . , , , , /, .

- OllyDbg , CreateRemoteThread()

.

push param1
push param2
push param3
call <____>
int3
int3
int3

( ), , int3 — , ( ) -.

, , , OllyDbg . , . , .

, , .

, , №2 — - . , .

«» :

Exotic bug

, 0xC000026E

( 0xC000005

— STATUS_ACCESS_VIOLATION

, / ), 0x004436E8

. , , 0x00400000

EXE-, - ( ).

«», , ( , ), . , 0xC000026E

. , STATUS_VOLUME_DISMOUNTED

. OllyDbg - 0x004436E8

, , , OllyDbg?

, , :

OllyDbg.exe . , . , OllyDbg.exe, , «Go to address» — , :
- Ctrl+G, (, at

CommandBar, Ctrl+G).
, . 0x004436E8

— — , «Go to expression».
CS:EIP=001B:004436E8

004436E8

( ), 004436E8

, . , x86- , ( PE CR0 ) ( PG CR0 ).
() , — P (Present) PDE PTE .
#PF (Page Fault), .
Windows, (KiTrap0E()

→MmAccessFault()

→ .) — - ( ) ( , ( user-mode) VirtualAlloc

, , - , image-backed swap-backed copy-on-write ).
00443000

, , , image-backed.
- (h:\soft\odbg\ollydbg.exe

), , , H:\

, . , STATUS_VOLUME_DISMOUNTED

(0xC000026E

).

, . , , , (working set) , , , .

image alt ( ), OllyDbg , - VirtualQueryEx()

, - . — , ( ) , , , , .

, ( DLL, OllyDbg) H:\

. Markup Dumper , . , (), , ( «» , ) .

, , .

, , , , , ( EIP - ) .

- , , OllyDbg (names), , , .

: . , - , . (Oleh Yuschuk), ...

, , , , , , .

Process Explorer , . , , - . Process Explorer ( VAD-), — , ReadProcessMemory()

. , .

— , «», «», . , , — - OllyDbg OllyDbg. H:\

.

API- Insertname()

, name ( , - ) names. names — , (markup), .

, names?

{, , }. , — . : ( $O(n)$ ), , , , , , , , .
, (). , $O(lb(n))$ — , 30 . ( , ). , «» , .
, (RB, AVL, ..). , , ( ) , / , / .

, , «», . — , .

, OllyDbg OllyDbg _Insertname()

, :

iInsertname under the disassembler

, , EBX, ESI, EDI, — . , — VirtualAlloc()

VirtualFree()

, memcpy

, - OllyDbg .

- : Process Monitor ( FileMon), , - ( TEST.DLL

), - TEST.UDD

, TEST.ARG

( , ). ARG- , , , OllyDbg

- ARG-.

- OllyDbg , ARG-, . : ARG- OllyDbg. ARG- custom-, , , OllyDbg — , , , VirtualAlloc()

VirtualFree()

, , , (push 4

fProtect = 4

, fProtet = PAGE_READWRITE

).

: ARG-, . . , ARG-.

like_memcpy

( memcpy()

libc) ,

Arg3 = ...
Arg2 = ...
Arg1 = ...

count = ...
src = ...
dest = ...

, , clr = 8000FF

clr = (R=255 G=0 B=128)

ARG- , OllyDbg «Custom function descriptions», .

, RTFM twice.

, - — … , .

, ? - , . () — , .

( ), malloc()

/HeapAlloc()

, VirtualAlloc()

, (, 4 ) . , EDX*24, EDX , - . , 24 — .
Plugin Development Kit (PDK) , Insertname() Quickinsertname() Mergequicknames(), names — API- . , , .

API- Insertname()

, :

Arrangement of tags and comments

, , . Names, , — , , , 24 , 12 , DWORD- ( — , , ). 24 12, 2 — , .

, Insertname()

:

int Insertname(ulong addr,int type,char *name)
{
    //
    //    
    //

    if(addr == NULL ||
       name == NULL ||
       type == NM_ANYNAME || type == NM_NONAME)
    {
        return -1;
    }

    //
    // ,     name- 
    //

    if(!pNamesBlock) return -1;

    if(!(cNameEntriesCur < cNameEntriesMax) && cNameEntriesMax < 1000000)
    {
        //
        //       ,   
        //

        void* const pNewBlock = VirtualAlloc(NULL, 
            2 * cNameEntriesMax * sizeof(NAME_REC), 
            MEM_COMMIT, 
            PAGE_READWRITE);

        if(pNewBlock)
        {
            //
            //   ,      
            //   .
            //

            memcpy(pNewBlock, pNameBlock, cNameEntriesMax * sizeof(NAME_REC));
            VirtualFree(pNamesBlock, 0, MEM_RELEASE);

            //
            //        , 
            //  ,    
            //     .
            //

            pNamesBlock = (NAME_REC*)pNewBlock;
            cNameEntriesMax *= 2;
        }
    }

    //      00463FB0

, , name

NULL, , -1

. API-:

Insertname

Inserts new or replaces existing name of given type in the name table. If name is NULL or empty, entry is deleted. Returns 0 on success and -1 on error. Note: do not call this function between calls to Quickinsertname and Mergequicknames!

int Insertname(ulong addr,int type,char *name);**

Parameters:

addr — name address;

type — name type ( NM_xxx for predefined types);

name — name to insert. If name is NULL or empty, entry is removed from the name table.

. , - OllyDbg.

. OllyDbg OllyDbg, OllyDbg , OllyDbg , {, , } c «» «» ( NM_LABEL

NM_COMMENT

).


DWORD	Address
DWORD	Value
DWORD	NameType

, «Value» names, , - ASCII-. , , — - .

, , - ( ), . - .

, OllyDbg , VirtualAlloc DWORD , : , - .

, ?

Continuation of Insertname () Code

, : - , , , , VirtualAlloc

VirtualFree

memcpy

, , , strlen

memcpy

.

, name' , , , , , , — , .

, :

We continue to reverse the Insertname () function further

, . , :

    if(!(cbStringPoolUsed + TEXTLEN < cbStringPoolTotal))
    {
        char* pNewStringPool;
        int cbDesiredNewPoolSize;

        if(GlobVarC > 4096 || cbStringPoolTotal > 320000000)
            cbDesiredNewPoolSize = cbStringPoolTotal;
        else
            cbDesiredNewPoolSize = cbStringPoolTotal * 2;

        pNewStringPool = VirtualAlloc(NULL, 
                                      cbDesiredNewPoolSize, 
                                      MEM_COMMIT,
                                      PAGE_READWRITE);
        if(pNewStringPool)
        {
            int cchUsed = 0;
            int i;
            for(int i = 0; i < cNameEntriesCur; i++)
            {
                char* pszCurString = pNamesStringPool + pNamesBlock[i].Offset;
                int   cchCurString = strlen(pszCurString) + 1;

                memcpy(pNewStringPool + cchUsed, pszCurString, cchCurString);
                pNamesBloc[i].Offset = cchUsed;
                ccUsed += cchCurString;
            }

            VirtualFree(pNamesStringPool, 0, MEM_RELEASE);

            pNamesStringPool = pNewStringPool;
            cbStringPoolUsed  = cchUsed;       
            cbStringPoolTotal = cbDesiredNewPoolSize;
            GlobalVarC = 0;
        }
    }

, (, - name', ) , (), , 320 , - ( GlobVarC

) 4096.

, memcpy

? , — ( , , ). , , , - , . , , , , 320 GlobVarC

> 4096. , GlobVarC

— , (delayed) . , / .

OllyDbg

, , , cbStringPoolUsed + TEXTLEN < cbStringPoolTotal

,

    cchCurString = strlen(Value) + 1;
    if(!(cbStringPoolUsed + cchCurString < cbStringPoolTotal))

-, , , , 5 , 100 , , 256 ( TEXTLEN

), .

-, 256 , - . , 255 , .

, strlen(value)

, Insertname()

, 255 !

1000 , Findname()

Findnextname()

, , .

, TEXTLEN

, , . . , , , — , - , . , , , , .

, 255 ?

-, , Insertname()

. , watch expressions, , , — name-. , 255 , .

-, OllyDbg , TEXTLEN

, . , Insertname()

Quickinsertname()

, . . , , OllyScript, . , , , .

OllyDbg (, ).

CNFFMappedStream::Unmap

, ?Unmap@CNFFMappedStream@@UAGXEPAPAX@Z

, OllyDbg « ». . , , . :

virtual void __stdcall CNFFMappedStream::Unmap(unsigned char,void * *)

. . , , COMDAT folding.

COMDAT folding?

, . , , , , , , . , , , , , , COMDAT ( Communal Data).

« » : COMDAT, ( , , , ; , COMDAT- , , ). — COMDAT , . "ERROR"

, — , . , , --.

unsigned short GetCodepointLength(const char* pCodepoint)
{
#ifdef UNICODE_STRINGS
#if UNICODE_STINGS == UTF8
    const char cp = *pCodepoint;
    unsigned short cbExtra;
    for(cbExtra = 0; (cp & 0x80) && (cbExtra < 3); cbExtra++, cp<<=1) 
        if(cp & 0x40) {if(!(cp & 0x20)) break; } else return 0;
    return 1 + cbExtra;
#else // UCS-2 or UTF-16
    return sizeof(wchar_t);
#endif
#else
    return sizeof(char);
#endif
}

LONG __stdcall CFlatArrayObject::GetDimensionsCount() // for IArrayObject::GetDimensionsCount
{
    return 1;
}

BOOL CAudioCodec::IsSampleFormatSupported(SAMPLE_FORMAT sf)
{
    return TRUE; // We support all
}

mov eax, 00000001
retn 4

( Microsoft ) COMDAT-folding . .

, COMDAT folding' , , « », , //

«FOLDED:

». COMDAT-folding' ( COM COM-, E_NOTIMP

— 5—6 , , , RETN

). , . , TEXTLEN

. ? OllyScript .

API- , , , , .

, «» Insertname()

, , , , ( ):

Global variables describing data blocks

PE- (EXE DLL) : ( ) swap-backed , image-backed, copy-on-write image-backed swap-backed, / / , PE-.

, ( , , OllyDbg , , , , .bss

) , OllyDbg ( ), , , swap-backed-.

H:\

( SSD-), OllyDbg.exe, , , ReadProcessMemory()

.

— , , , — , . , ( ) , - , , , .

, — , , , — :

NAME_REC

, {, , }. 12 . «» . .
, -, (, ..). «» , , . .

OllyDbg.exe

, — .

Two data blocks

, . , , , — , 7 ( 4 ).

, . 1.10. ! 1.10, , OllyDbg, , .

, 0x004EAE14

, , , , , OllyDbg. : — API- Insertname()

. ( , ). API- . , , . , , , , VirtualFree

, , VirtualAlloc

.

, . OllyDbg , , - (ollydbg.exe

), , - . «» , , . -, , , :

struct
{
    struct 
    {
        DWORD pNamesBlock;
        DWORD cNameEntriesCur;
        DWORD cNameEntriesMax;
    } NameBlockInfo;

    struct
    {
        DWORD pNamesStringPool;
        DWORD cbStringPoolUsed;
        DWORD cbStringPoolTotal;
        DWORD wtf;
    } StringPool;
} Metadata;

void main()
{
    HANDLE hOdbgProc;
    DWORD cbRead = 0;
    DWORD pid = ?????????;

    hOdbgProc = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pid);

    ReadProcessMemory(hOdbgProc, 
        (LPCVOID)0x004EAE14, 
        &Metadata.NameBlockInfo,
        sizeof(Metadata.NameBlockInfo),
        &cbRead))

    ReadProcessMemory(hOdbgProc, 
        (LPCVOID)0x004EAE30,
        &Metadata.StringPool, 
        sizeof(Metadata.StringPool),
        &cbRead))

    VOID* pNamesBlock;
    VOID* pNamesPool;

    pNamesBlock = VirtualAlloc(0, Metadata.NameBlockInfo.cNameEntriesMax * 12, MEM_COMMIT, PAGE_READWRITE);
    pNamesPool = VirtualAlloc(0, Metadata.StringPool.cbStringPoolTotal, MEM_COMMIT, PAGE_READWRITE);

    ReadProcessMemory(hOdbgProc, 
                      (LPCVOID)Metadata.NameBlockInfo.pNamesBlock,
                      pNamesBlock,
                      Metadata.NameBlockInfo.cNameEntriesMax * 12,
                      &cbRead))

    ReadProcessMemory(hOdbgProc, 
                      (LPCVOID)Metadata.StringPool.pNamesStringPool,
                      pNamesPool,
                      Metadata.StringPool.cbStringPoolTotal,
                      &cbRead))

    DumpBlockToFile(&Metadata,  sizeof(Metadata), "names-meta.dat");
    DumpBlockToFile(pNamesBlock, Metadata.NameBlockInfo.cNameEntriesMax * 12, "names-tbl.dat");
    DumpBlockToFile(pNamesPool,  Metadata.StringPool.cbStringPoolTotal, "names-pool.dat");

    VirtualFree(pNamesBlock, 0, MEM_RELEASE);
    VirtualFree(pNamesPool,  0, MEM_RELEASE);
}

— , , ReadProcessMemory

. , - , - — , , , -, . , ( ), - — OllyDbg.

Dumping by OllyDbg

, , OllyDbg, , - , .

- , , , , . , , , . , .

- , , , . , , , - ?

VirtualAlloc()

, , (4K x86). - 0x00000FFF , .
, VirtualAlloc()

Insertname()

- , , , SYSTEM_INFO::dwAllocationGranularity, x86 64K. 16 , .
VirtualQueryEx()

, () VirtualAlloc()

, ( PAGE_READWRITE

), , .
, «» .
( ) , , — . , , 32- , 640 . , , , NM_xxxx

, PDK.
( ) - , . , - , ( ), — , (.. ). , , .
, , ( ).

, - , « » — , . , API- Insertname

, , .

?

, . . ?

, :

, Markup Dumper, , , ( , ). , OllyDbg. , 5 , . ( ) .
«» , ( , ) OllyDbg, API-, . .. Insertname()

( ). , UDD-.
, , — OllyDbg , / . UDD-. - , . , , , .

, , . , :

typedef struct
{
    DWORD Va;      // virtual address of NAME in debugger process
    DWORD Offset;  // offset of NAME's value in string pool
    DWORD Type;    // one of NM_xxxxx values
} NAME_REC;

, for

-, cNameEntriesCur

Insertname()

, , .

P.S. . , , , , . , howto-, , , - Git VCS, - API- OllyDbg, OllyDbg, Windows . , , , , , - .

OllyDbg on death - saving the workings of the debug session

Insertname

?

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