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Cheat engine dbk

 
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Viloresi
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Joined: 02 Feb 2017
Posts: 144

PostPosted: Tue Aug 06, 2019 2:35 pm    Post subject: Cheat engine dbk Reply with quote

So I'm trying to make a driver that does these things (I'm not an expert and I lack a lot of knowledge tbh) :
1)Sets a breakpoint on an address
2)Change the EAX register on that address to 1
3) continues execution

I would like to do this through a driver like cheat engine does with dbk.
I've already taken a look at the source code, but I quite didn't understand how it works because I've seen in the dbk source code it uses this function:
__writedr(0,value);
to write in db registers but I don't understand what's the first parameter and also after the breakpoint is set where is the code that handles the breakpoint? is there an exception raised or some other things I can't see in the source??,hmm anyway if someone could provide a code snippet might be better but everything is accepted, thank you for reading.
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Dark Byte
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PostPosted: Tue Aug 06, 2019 3:21 pm    Post subject: Reply with quote

you're imeadiately delving into the deep end, but ok

:

there are 6 debug registers
0, 1,2,3,6 and 7

set dr0 to the address
set dr7 the configuration to break. (execute,read/write, write only, and size applicable)

but the important part is the exception or interrupt handler (good luck with pathguard in 64 bit) in there you decide on passing the exception to the target or handling it yourself

https://software.intel.com/en-us/download/intel-64-and-ia-32-architectures-sdm-combined-volumes-1-2a-2b-2c-2d-3a-3b-3c-3d-and-4

i recommend reading and understanding everything, but especially volume 3 and the chapters about interrupts (6) and debugging (17) is important

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Viloresi
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Joined: 02 Feb 2017
Posts: 144

PostPosted: Tue Aug 06, 2019 3:52 pm    Post subject: Reply with quote

Dark Byte wrote:
you're imeadiately delving into the deep end, but ok

:

there are 6 debug registers
0, 1,2,3,6 and 7

set dr0 to the address
set dr7 the configuration to break. (execute,read/write, write only, and size applicable)

but the important part is the exception or interrupt handler (good luck with pathguard in 64 bit) in there you decide on passing the exception to the target or handling it yourself

https://software.intel.com/en-us/download/intel-64-and-ia-32-architectures-sdm-combined-volumes-1-2a-2b-2c-2d-3a-3b-3c-3d-and-4

i recommend reading and understanding everything, but especially volume 3 and the chapters about interrupts (6) and debugging (17) is important

thank you, wow that's 4922 pages , thinking to study that right now for me it's probably not a good choice bcs I'll have a math exam in about 1 month. I guess I'll look into this when I'll have more freetime

anyway I was trying to do this in a c++ program (not with a driver) by setting a VEH hook to the target address, by changing as you said dr0 by writing inside the address and writing 0x401 in dr7 (which if I understood correctly enables the dr0), but unfortunately it doesn't work and in some programs it crashes...
I think I'll open a new thread about it since it's a different argument
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