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Getting a module's base address and bound

Posted on 2007-08-09
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How can I obtain a module's base address and bound in memory? I have a DLL that I wrote, which is being loaded by an EXE (that I did *not* write) as a CBT Hook. I want to muddle with the memory of the EXE and alter a few instructions. I know the pattern I'm searching for and what I want to replace it with, but can't figure out how to obtain the base address to start searching from on-the-fly, as well as the ending address for that EXE module.

I want to dynamically find the base address and bound somehow, since the default base address specified in the PE header isn't always available and Windows can shift things around.
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Question by:jimstar
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jkr earned 2000 total points
ID: 19663339
>>How can I obtain a module's base address and bound in memory?

The base address is avialble via

LPVOID pvBaseAddr = (LPVOID) GetModuleHandle("mymodule.dll");

What do you mean by "bound"?
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by:grg99
ID: 19663785
I think there are some useful functions for this in the ToolHelp API.

You can also approach it with the debugging API or Read/WriteProcessMemory.

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by:jimstar
ID: 19666043
Thanks, I didn't realize that the HMODULE returned from GetModuleHandle is actually a pointer to the base address of the module. By 'bound' I mean the size of the module or ending address, so when I'm searching for a particular byte pattern in the module's memory, I don't go past the end of that module.
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by:jkr
ID: 19666128
For the size, you can use


MEMORY_BASIC_INFORMATION mbi;
LPVOID pvBaseAddr = (LPVOID) GetModuleHandle("mymodule.dll");

VirtualQuery (pvBaseAddr, &mbi, sizeof ( mbi));

// 'size' is mbi.RegionSize
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by:jkr
ID: 19666163
Oh, BTW, you will need to use the MEMORY_BASIC_INFORMATION along with the size from above to to remove the 'readonly' attribute from the memory pages before altering anything, i.e.

DWORD dwProtect = mbi.Protect & ~PAGE_READONLY;
DWORD dwOld; // dummy

VirtualProtect(pvBaseAddr,mbi.RegionSize,dwProtect,&dwOld);
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