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The Thread Local Storage (TLS) contains static or global values for a thread. Those values can be very important to find reliable references to memory structures when the memory locations are not static.

I would like to get the Thread Local Storage of another process.

The TLS should be at [FS:0x2C] in the Thread Information Block (TIB). Though I quite don't understand how the FS register works. I guess I have to find the TIB Base address first? I think I can find it in the Thread Context I can get with WINAPI GetThreadContext, but I am a little bit overwhelmed.

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  • Are you looking for ways to access it in the same process? different process? Clarify your situation and what exactly you need to do.
    – Igor Skochinsky ♦
    Dec 7 '13 at 0:36
  • I try to do it for a different process. I will update my question for clarification.
    – samuirai
    Dec 7 '13 at 0:49
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You need to use GetThreadSelectorEntry().

Pseudocode:

GetThreadContext(hThread, &context);
GetThreadSelectorEntry(hThread, context.SegFs, &selectorEntry);
ReadProcessMemory(hProcess, (selectorEntry.BaseLow | (selectorEntry.HighWord.Bytes.BaseMid << 0x10) | (selectorEntry.HighWord.Bytes.BaseHi << 0x18)) + 0x2C, &pTLS, sizeof(pTLS), &numberOfBytesRead);

You can see the function GetProcessEntryPointAddress() here for some sample code that does something similar.

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  • thank you, it worked like a charm :) I didn't know GetThreadSelectorEntry()
    – samuirai
    Dec 7 '13 at 20:00

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