ReadProcessMemory fails on some Pages (GetLastError()=299)

Question

I try to read all commited pages of a process (Win7-64). On most pages it works but it fails for a few pages. I cannot explain why. Here is my test programme (compiled x32,

Answer 1

A little bit of debugging and something interesting is identified: all pages that fail have protection bit PAGE_GUARD set (see MSDN doc). As I interpret the docs, it is by design that you cannot read these pages with ReadProcessMemory.

if(ReadProcessMemory(hProc, baseOffs,buf,si.dwPageSize,&numByteWritten) == FALSE) {
    assert(mbi.Protect & 0x100);
    OutputDebugString(TEXT("bad\n")); //GetLastError()==ERROR_PARTIALLY_READ; numByteWritten == 0; 
}
else {
    assert(!(mbi.Protect & 0x100));
    OutputDebugString(TEXT("good\n")); 
}