memory breakpoints like olly

[snoopy]

Hey Guys I am having a question about memory breakpoints, like Olly implements.

The main issue is that doing it myself with a dll I am injecting into the process, the concept is extremely slow.

While breakpointing with Olly it's just as fast as any other breakpoints.

I am having a spot inside the program I want to set the breakpoint on.

I copied this spot into a variable called: [HardwareBreakpointAddress]

I am hooking KiUserExceptionDispatcher to catch the exceptions. I know I could also install a Vectored Exception Handler but this seems to suit just fine aswell.

The code is WORKING, it's just I am wondering why it is so terrible slow.

Is it because of the way the trapflag is being set?

Export KiUserExceptionDispatcher_hook:

;-------------------------------------------------------------

;ntdll!KiUserExceptionDispatcher:

;7de80124 fc cld

;7de80125 8b4c2404 mov ecx,dword ptr [esp+4] //

;7de80129 8b1c24 mov ebx,dword ptr [esp] //

;-------------------------------------------------------------

cld

mov ecx, D[esp+04h] //Pointer to the context record

mov ebx, D[esp] //Pointer to the exception record

pushad

cmp D[ebx], EXCEPTION_SINGLE_STEP //Single Step Exception 0x80000004

je > __checkdrx

jmp > __checkpg

__checkdrx:

push ecx

mov esi, ecx

invoke SetSingleStepMode, [MainThreadIdHandle], FALSE // clear trap flag

invoke VirtualProtect, [HardwareBreakpointAddress], 1, PAGE_EXECUTE_READWRITE | PAGE_GUARD, offset OldProtection

pop ecx

jmp > __allgood

__done:

mov eax, [esi+CONTEXT.Eax]

mov [breakPointValue], eax

xor eax, eax

invoke ResumeThread, [DLLThreadHandle]

invoke SuspendThread, [MainThreadIdHandle]

__allgood:

popad

invoke NtContinue, ecx, 1

nop

nop

__checkpg:

cmp D[ebx], STATUS_GUARD_PAGE_VIOLATION

jne > __goback

push ecx

mov esi, ecx

mov eax, [esi+CONTEXT.Eip]

cmp eax, [HardwareBreakpointAddress]

je < __done

invoke VirtualProtect, [HardwareBreakpointAddress], 1, PAGE_EXECUTE_READWRITE, offset OldProtection

invoke SetSingleStepMode, [MainThreadIdHandle], TRUE // set trap flag

jmp < __allgood

__goback:

popad

push [KiUserExceptionDispatcher_ret]

ret

SetSingleStepMode Frame pThread, bSet

//If bSet==1 then set the single step, otherwise unset it.

mov [context.ContextFlags], CONTEXT_FULL

invoke GetThreadContext, [pThread], offset context

cmp B[bSet], 0

je >

or W[context.ContextFlags], 0100h // set trap flag

jmp > SetFlagContext

:

and W[context.ContextFlags], 0FEFFH // clear trap flag

SetFlagContext:

invoke SetThreadContext, [pThread], offset context

ret

Endf

Edited June 9, 2014 by snoopy