Hooked VirtualAlloc returns nullptr when called by system DLLs

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Hooking system functions like VirtualAlloc can be complex and might lead to unexpected behavior, especially when system DLLs are involved. In some cases, the behavior you're observing might be due to the way hooking mechanisms work or how the operating system manages memory allocation.

Here are a few potential reasons why your hooked VirtualAlloc might return nullptr when called by system DLLs:

  1. Hooking Mechanism:
    The way you're hooking the VirtualAlloc function can influence its behavior. Ensure that your hooking mechanism is correctly intercepting the function call and returning the appropriate value. Improper hooking can result in unexpected consequences.

  2. Recursive Calls:
    Some system DLLs might internally call functions like VirtualAlloc, and if your hooking mechanism is not properly designed, it could lead to recursive calls, eventually resulting in a failed memory allocation.

  3. Compatibility and ABI:
    System DLLs have specific calling conventions and might expect certain behaviors from functions like VirtualAlloc. If your hooking code is not compatible with these expectations, it could result in unexpected failures.

  4. Order of Execution:
    The order in which hooks are executed can impact the behavior. If another hook or system code modifies the arguments or state of the VirtualAlloc function before your hook is executed, it could lead to issues.

  5. Memory Allocation Issues:
    If your hooking code consumes a significant amount of memory or modifies memory allocation flags improperly, it could affect subsequent memory allocations, including those performed by system DLLs.

  6. Access Rights and Privileges:
    System DLLs might have different access rights and privileges compared to regular application code. Your hooking code should take into account the privileges required for system DLLs.

  7. Debugging and Profiling:
    Debugging and profiling tools can help you identify where the problem is occurring. Tools like WinDbg or Visual Studio's debugger can assist in analyzing the behavior of your hooking code.

  8. Compatibility with System DLLs:
    Some system DLLs might be sensitive to modification or interception of their internal functions. It's important to thoroughly understand the behavior and requirements of the specific DLLs you're dealing with.

  9. Operating System and Security:
    Certain security mechanisms or operating system features might interfere with your hooking attempts, especially when interacting with critical system functions.

  10. Alternative Approaches:
    Depending on your goals, consider alternative approaches that avoid hooking system functions. For example, you might use code injection techniques that work more seamlessly with system DLLs.

It's important to thoroughly test and validate your hooking code under various scenarios, including interactions with system DLLs. Keep in mind that hooking system functions can be complex, and unexpected consequences can arise due to the intricate interactions within the operating system.