How to get list of GDI handles
See the question and my original answer on StackOverflowHere is a console application code that dumps all GDI handles out for a given process identifier. It should compile and work fine for 32 or 64-bit applications, as well as 32-bit application running on 64-bit OSes. It uses a lot of undocumented functions so don't rely on it :-) Credits on structures for the shared GDI table goes to Feng Yuan original work. (I had to adapt it for WOW64).
Here is a sample output when ran on a Notepad (64-bit) process:
[C:\Temp\EnumGdi\Debug]EnumGdi.exe 5916
DC handle:0xF20105DB
Bitmap handle:0xDF05118B
Font handle:0xDC0A19E0
Font handle:0xAB0A1A62
DC handle:0xA3011A63
Region handle:0xAF041B7B
Brush handle:0x11101C5B
Font handle:0x280A1CA1
Font handle:0xBB0A1D13
Bitmap handle:0xA3051DD8
Font handle:0xB40A1DDC
Region handle:0x3A041EE4
Brush handle:0x0B101F04
Region handle:0xC6041F3D
Font handle:0x2C0A2384
Brush handle:0xBA1024DA
EnumGdi.cpp:
#include "stdafx.h"
#include "enumgdi.h"
int _tmain(int argc, _TCHAR* argv[])
{
if (argc < 2)
{
printf("Format is EnumGdi <process id>\n");
return 0;
}
// get process identifier
DWORD dwId = _wtoi(argv[1]);
// open the process
HANDLE hProcess = OpenProcess(PROCESS_QUERY_INFORMATION | PROCESS_VM_READ, FALSE, dwId);
DWORD err = 0;
if (hProcess == NULL)
{
printf("OpenProcess %u failed\n", dwId);
err = GetLastError();
return -1;
}
// determine if 64 or 32-bit processor
SYSTEM_INFO si;
GetNativeSystemInfo(&si);
// NOTE: as this is undocumented, it *may vary* depending on bitness (32/64) and on Windows version.
// use WinDbg "dt ntdll!_PEB" command and search for GdiSharedHandleTable offset to find the truth out
DWORD GdiSharedHandleTableOffset = si.wProcessorArchitecture == PROCESSOR_ARCHITECTURE_AMD64 ? 0xF8 : 0x94;
DWORD tableCount = 16384; // count of GDI table cells
// determine if this process is running on WOW64
BOOL wow;
IsWow64Process(GetCurrentProcess(), &wow);
// read basic info to get PEB address, we only need the beginning of PEB
DWORD pebSize = GdiSharedHandleTableOffset + 8;
LPBYTE peb = (LPBYTE)malloc(pebSize);
ZeroMemory(peb, pebSize);
if (wow)
{
// we're running as a 32-bit process in a 64-bit process
PROCESS_BASIC_INFORMATION_WOW64 pbi;
ZeroMemory(&pbi, sizeof(pbi));
// get process information from 64-bit world
_NtQueryInformationProcess query = (_NtQueryInformationProcess)GetProcAddress(GetModuleHandleA("ntdll.dll"), "NtWow64QueryInformationProcess64");
err = query(hProcess, 0, &pbi, sizeof(pbi), NULL);
if (err != 0)
{
printf("NtWow64QueryInformationProcess64 failed\n");
CloseHandle(hProcess);
return -1;
}
// read PEB from 64-bit address space
_NtWow64ReadVirtualMemory64 read = (_NtWow64ReadVirtualMemory64)GetProcAddress(GetModuleHandleA("ntdll.dll"), "NtWow64ReadVirtualMemory64");
err = read(hProcess, pbi.PebBaseAddress, peb, pebSize, NULL);
if (err != 0)
{
printf("NtWow64ReadVirtualMemory64 PEB failed\n");
CloseHandle(hProcess);
return -1;
}
// get GDI table ptr from PEB
GDICELL_WOW64* gdiTable = (GDICELL_WOW64*)*(LPVOID*)(peb + GdiSharedHandleTableOffset); // address in remote process adress space
if (gdiTable == NULL)
{
printf("GDI32.DLL is not loaded in the process\n");
CloseHandle(hProcess);
return -1;
}
free(peb);
DWORD tableSize = sizeof(GDICELL_WOW64) * tableCount; // size of GDI table
GDICELL_WOW64* table = (GDICELL_WOW64*)malloc(tableSize); // local table copied over to our address space
// copy GDI table
err = read(hProcess, gdiTable, table, tableSize, NULL);
if (err != 0)
{
printf("NtWow64ReadVirtualMemory64 GdiTable failed\n");
free(table);
CloseHandle(hProcess);
return -1;
}
for(DWORD i = 0; i < tableCount; i++)
{
GDICELL_WOW64 cell = table[i];
if (cell.wProcessId != dwId)
continue;
HGDIOBJ gdiHandle = (HGDIOBJ)((cell.wUpper << 16) + i);
WORD type = cell.wType & 0x7F;
switch(type)
{
case 1:
printf("DC handle:0x%08X\n", gdiHandle );
break;
case 4:
printf("Region handle:0x%08X\n", gdiHandle);
break;
case 5:
printf("Bitmap handle:0x%08X\n", gdiHandle);
break;
case 8:
printf("Palette handle:0x%08X\n", gdiHandle);
break;
case 10:
printf("Font handle:0x%08X\n", gdiHandle);
break;
case 16:
printf("Brush handle:0x%08X\n", gdiHandle);
break;
case 48:
printf("Pen handle:0x%08X\n", gdiHandle);
break;
default:
printf("Unknown type handle:0x%08X\n", gdiHandle);
break;
}
}
free(table);
}
else
{
// we're running as a 32-bit process in a 32-bit OS, or as a 64-bit process in a 64-bit OS
PROCESS_BASIC_INFORMATION pbi;
ZeroMemory(&pbi, sizeof(pbi));
// get process information
_NtQueryInformationProcess query = (_NtQueryInformationProcess)GetProcAddress(GetModuleHandleA("ntdll.dll"), "NtQueryInformationProcess");
err = query(hProcess, 0, &pbi, sizeof(pbi), NULL);
if (err != 0)
{
printf("NtQueryInformationProcess failed\n");
CloseHandle(hProcess);
return -1;
}
// read PEB
_NtReadVirtualMemory read = (_NtReadVirtualMemory)GetProcAddress(GetModuleHandleA("ntdll.dll"), "NtReadVirtualMemory");
err = read(hProcess, pbi.PebBaseAddress, peb, pebSize, NULL);
if (err != 0)
{
printf("NtReadVirtualMemory PEB failed\n");
CloseHandle(hProcess);
return -1;
}
// get GDI table ptr
GDICELL* gdiTable = (GDICELL*)*(LPVOID*)(peb + GdiSharedHandleTableOffset); // address in remote process adress space
if (gdiTable == NULL)
{
printf("GDI32.DLL is not loaded in the process\n");
CloseHandle(hProcess);
return -1;
}
free(peb);
DWORD tableSize = sizeof(GDICELL) * tableCount; // size of GDI table
GDICELL* table = (GDICELL*)malloc(tableSize); // local table copied over to our address space
// read GDI table
err = read(hProcess, gdiTable, table, tableSize, NULL);
if (err != 0)
{
printf("NtReadVirtualMemory GdiTable failed\n");
free(table);
CloseHandle(hProcess);
return -1;
}
for(DWORD i = 0; i < tableCount; i++)
{
GDICELL cell = table[i];
if (cell.wProcessId != dwId)
continue;
HGDIOBJ gdiHandle = (HGDIOBJ)((cell.wUpper << 16) + i);
WORD type = cell.wType & 0x7F;
switch(type)
{
case 1:
printf("DC handle:0x%08X\n", gdiHandle );
break;
case 4:
printf("Region handle:0x%08X\n", gdiHandle);
break;
case 5:
printf("Bitmap handle:0x%08X\n", gdiHandle);
break;
case 8:
printf("Palette handle:0x%08X\n", gdiHandle);
break;
case 10:
printf("Font handle:0x%08X\n", gdiHandle);
break;
case 16:
printf("Brush handle:0x%08X\n", gdiHandle);
break;
case 48:
printf("Pen handle:0x%08X\n", gdiHandle);
break;
default:
printf("Unknown type handle:0x%08X\n", gdiHandle);
break;
}
}
free(table);
}
CloseHandle(hProcess);
}
EnumGdi.h:
#pragma once
#include "stdafx.h"
// defines a GDI CELL
typedef struct
{
LPVOID pKernelAddress;
USHORT wProcessId;
USHORT wCount;
USHORT wUpper;
USHORT wType;
LPVOID pUserAddress;
} GDICELL;
// defines a GDI CELL for WOW64
typedef struct
{
PVOID64 pKernelAddress;
USHORT wProcessId;
USHORT wCount;
USHORT wUpper;
USHORT wType;
PVOID64 pUserAddress;
} GDICELL_WOW64;
// NtQueryInformationProcess for pure 32 and 64-bit processes
typedef NTSTATUS (NTAPI *_NtQueryInformationProcess)(
IN HANDLE ProcessHandle,
ULONG ProcessInformationClass,
OUT PVOID ProcessInformation,
IN ULONG ProcessInformationLength,
OUT PULONG ReturnLength OPTIONAL
);
typedef NTSTATUS (NTAPI *_NtReadVirtualMemory)(
IN HANDLE ProcessHandle,
IN PVOID BaseAddress,
OUT PVOID Buffer,
IN SIZE_T Size,
OUT PSIZE_T NumberOfBytesRead);
// NtQueryInformationProcess for 32-bit process on WOW64
typedef NTSTATUS (NTAPI *_NtWow64ReadVirtualMemory64)(
IN HANDLE ProcessHandle,
IN PVOID64 BaseAddress,
OUT PVOID Buffer,
IN ULONG64 Size,
OUT PULONG64 NumberOfBytesRead);
// PROCESS_BASIC_INFORMATION for pure 32 and 64-bit processes
typedef struct _PROCESS_BASIC_INFORMATION {
PVOID Reserved1;
PVOID PebBaseAddress;
PVOID Reserved2[2];
ULONG_PTR UniqueProcessId;
PVOID Reserved3;
} PROCESS_BASIC_INFORMATION;
// PROCESS_BASIC_INFORMATION for 32-bit process on WOW64
// The definition is quite funky, as we just lazily doubled sizes to match offsets...
typedef struct _PROCESS_BASIC_INFORMATION_WOW64 {
PVOID Reserved1[2];
PVOID64 PebBaseAddress;
PVOID Reserved2[4];
ULONG_PTR UniqueProcessId[2];
PVOID Reserved3[2];
} PROCESS_BASIC_INFORMATION_WOW64;