readprocessmemory error 299[通俗易懂]

全栈程序员-站长 • 2022年10月4日下午5:16 • 未分类 • 阅读 2

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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, tested in Win7-64):

#include <windows.h> void main() { 
    HANDLE hProc = OpenProcess(PROCESS_VM_READ | PROCESS_QUERY_INFORMATION,FALSE,GetCurrentProcessId()); SYSTEM_INFO si; ZeroMemory(&si,sizeof(SYSTEM_INFO)); GetSystemInfo(&si); char* buf = new char[si.dwPageSize]; for (unsigned i = 0; i < 0x7fff0; i++) { 
    void* baseOffs = (void*) (i * si.dwPageSize); MEMORY_BASIC_INFORMATION mbi; ZeroMemory(&mbi,sizeof(MEMORY_BASIC_INFORMATION)); if (VirtualQueryEx(hProc, baseOffs, &mbi, sizeof(MEMORY_BASIC_INFORMATION)) == 0) { 
    MessageBox(NULL, TEXT("VirtualQueryEx failed"),TEXT(""),MB_OK); } if (mbi.State == MEM_COMMIT) { 
    SIZE_T numByteWritten = 0; if(ReadProcessMemory(hProc, baseOffs,buf,si.dwPageSize,&numByteWritten) == FALSE) OutputDebugString(TEXT("bad\n")); //GetLastError()==ERROR_PARTIALLY_READ; numByteWritten == 0; else OutputDebugString(TEXT("good\n")); } } delete[] buf; }

I tired to look into the MEMORY_BASIC_INFORMATION for the failing pages but I didn’t find anything strange there. Also the number of failing pages varies from run to run (in average about 5). WHat prevents me from reading these pages? Do I need to adjust some privilges in the process token?

A little bit of debugging and somethings 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")); }