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I am studying assembly and hooking.

I know how to hook x86 assembly now. so if any thread goes to certain address which is overwritten with my code, it automatically returns to my function. I think this is normal hooking principle. https://www.apriorit.com/dev-blog/160-apihooks

And now, I want to hook x86 registers or memory in windows 32bit, like almost debugger's breakpoints do. So when some memory areas are accessed, automatically call my function in that process memory. To be exact, I want to use my hooked function instead of breakpoint. Any advance will be appreciated!

  • Welcome to RE.SE! Uhm, actually setting a breakpoint will in fact - through operating system facilities - typically end up as some kind of "hook function" being called. Alas you don't specify the environment (such as the OS) you're running in and it's not exactly clear what you're looking for, given how breakpoints pretty much already achieve what you want (in particular hardware-assisted breakpoints, whose number is limited, though). – 0xC0000022L Aug 17 '18 at 11:21
  • Thank your for approaching to my problem. 1. I am using windows x32. I think the OS is not a problem. 2. I know about hardware breakpoint. I want sth similar to hardware breakpoint, but I want a function called when condition is matched, instead of breakpoint. Thank you – Luis Bergmann Aug 17 '18 at 13:09
  • @LuisBergmann: Please, edit your question to add these information in it (and add some tags about your OS and the CPU architecture targeted). – perror Aug 17 '18 at 15:30
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The only way this can be accomplished, in my opinion, is to override the Page Fault Handler. You cannot do this in user mode, however. The hooks you cite deal with user mode DLL entry points, which is easy to achieve. The paging mechanism is implemented in the kernel, at Ring 0, so basically you will need to write a driver which, in case of a Page Fault, checks if the address is in the range you want monitored and, if yes, calls your function; otherwise calls the default kernel routines. Quite tricky to do, especially on Windows (Linux is somewhat easier) and you risk in de-stabilizing the entire system.

This is what kernel-mode debuggers such as SoftICE (https://en.wikipedia.org/wiki/SoftICE) or WinDbg (https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/getting-started-with-windbg--kernel-mode-) do.

If you really want to go for it, a good starting point for information is here: https://stackoverflow.com/questions/18431261/how-does-x86-paging-work and of course https://docs.microsoft.com/en-us/windows-hardware/drivers/

PS: No way to do it for registers

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