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Windows Virtual Address Space

as I read here the virtual address space of a 32 bit Windows application has 2GB of storage (from 0x00000000-0x7FFFFFFF). The other 2GB are reserved for the system address space.

However, I found a pointer in a 32bit program (using Cheat Engine) which is pointing to an address which isn't in range of the virutal address space. The addresses in my last exploration were 0x301DDC3C -> 0x87F56190 like you can see in the picture: enter image description here

(The expansion in the first line means a dereference of the pointer 0x301DDC3C, in the next line you can see what's in the dereference location 0x87F56190 in RAM)

After dereferencing the pointer there are pointers back into the process virtual address space.

How is it possible that a user mode application has a valid pointer into system address space?

Does this mean the pointer in location 0x301DDC3C is pointing to an location in the system address space? And so the process I'm examining is using kernel mode stuff?

Solution

  • from Memory and Address Space Limits

    Limits on memory and address space vary by platform, operating system, and by whether the IMAGE_FILE_LARGE_ADDRESS_AWARE flag in the IMAGE_FILE_HEADER.Characteristics. IMAGE_FILE_LARGE_ADDRESS_AWARE (The application can handle addresses larger than 2 GB) is set or cleared by using the /LARGEADDRESSAWARE linker option.

    by default IMAGE_FILE_LARGE_ADDRESS_AWARE cleared for 32-bit PE and set for 64-bit PE, but we can overwrite default:

    enter image description here

    so 32-bit process with set IMAGE_FILE_LARGE_ADDRESS_AWARE flag - up to 4Gb memory is avaible.

    really of course [0, 0x800000000000) (win8.1 +) or [0, 0x80000000000) (before win 8.1) memory space is avaible for user mode in x64 windows. but system artificially restrict this by reserve big range of memory (this allocation is protected and can not be free)

    for 32-bit process this reservation begin from 7FFF0000 or FFFE0000 and up to 64-bit ntdll.dll. very interesting that in 64-bit process, where IMAGE_FILE_LARGE_ADDRESS_AWARE cleared - also was such reserved memory space begin from 0x80000000. also interesting that in this case kernel32.dll is loaded at another address compare usual 64-bit process. so base of kernel32.dll not the same in general in all 64-bit processes. but ntdll.dll loaded at the same address in all processes anyway.

    usual memory allocations on x64 windows:

    1. 32 bit process, IMAGE_FILE_LARGE_ADDRESS_AWARE cleared (default) enter image description here
    2. 32 bit process, IMAGE_FILE_LARGE_ADDRESS_AWARE set enter image description here
    3. 64 bit process, IMAGE_FILE_LARGE_ADDRESS_AWARE cleared enter image description here
    4. 64 bit process, IMAGE_FILE_LARGE_ADDRESS_AWARE set (default) enter image description here