How to enum modules in a 64bit process from a 32bit WOW process

Question

I have a requirement to retrieve all modules of a 64bit process in a 32bit WOW process in Windows, EnumProcessModules would fail as described:

If this function is called from a 32-bit application running on WOW64, it can only enumerate the modules of a 32-bit process. If the process is a 64-bit process, this function fails and the last error code is ERROR_PARTIAL_COPY (299).

So as to EnumProcessModulesEx and CreateToolhelp32Snapshot.

Do you have any idea on how to achieve it?

Thanks.

Answer 1

Without going into undocumented APIs, you can't do this. In general, reading a 64-bit process' memory from a 32-bit process won't work due to the address space differences.

EnumProcessModulesEx, which has LIST_MODULES_32BIT and LIST_MODULES_64BIT filter flags, has this to say:

This function is intended primarily for 64-bit applications. If the function is called by a 32-bit application running under WOW64, the dwFilterFlag option is ignored and the function provides the same results as the EnumProcessModules function.

You could do this by converting your program to 64-bit, using an out-of-proc 64-bit COM server (specifically using a DLL surrogate), or having a separate process that you communicate with. Alternatively, depending on when your process starts relative to your target process, you could use WMI to get module load events. See the Win32_ModuleLoadTrace event.

Process Explorer, a single 32-bit exe, can show you modules for both 32- and 64-bit processes, but it's really smoke and mirrors: the 32-bit exe contains a 64-bit version of itself that gets written out to disk and executed on 64-bit machines.

Answer 2

Solution for your request has some intersections with the task of reading x64 process memory from x86 process. Mainly, we should be aware of functions NtWow64QueryInformationProcess64 and NtWow64ReadVirtualMemory64 which are present in x86 ntdll.dll and are designed specifically for getting information about x64 process from the x86 one.

We should also know some dependencies between OS structures.

PROCESS_BASIC_INFORMATION contains address of PEB. PEB stands for Process Environment Block. It contains address of PEB_LDR_DATA structure. It in turn contains address of the first LDR_DATA_TABLE_ENTRY structure in the LIST_ENTRY chain. LDR_DATA_TABLE_ENTRY contains link to the following LDR_DATA_TABLE_ENTRY.

Example of examining this information in WinDbg:

0:000> !peb
PEB at 000007fffffdb000
...

0:000> dt ntdll!_peb 000007fffffdb000
...
+0x018 Ldr              : 0x00000000`76fbd640 _PEB_LDR_DATA
...

0:000> dt ntdll!_PEB_LDR_DATA 76fbd640
...
+0x010 InLoadOrderModuleList : _LIST_ENTRY [ 0x00000000`00415bb0 - 0x00000000`070eb9c0 ]
...

0:000> dt ntdll!_LDR_DATA_TABLE_ENTRY 00415bb0
+0x000 InLoadOrderLinks : _LIST_ENTRY [ 0x00000000`00415ca0 - 0x00000000`76fbd650 ]
...
+0x030 DllBase          : 0x00000001`3f4d0000 Void
...
+0x058 BaseDllName      : _UNICODE_STRING "procexp64.exe"
...

0:000> dt ntdll!_LDR_DATA_TABLE_ENTRY 00415ca0
+0x000 InLoadOrderLinks : _LIST_ENTRY [ 0x00000000`00416020 - 0x00000000`00415bb0 ]
...
+0x030 DllBase          : 0x00000000`76e90000 Void
...
+0x058 BaseDllName      : _UNICODE_STRING "ntdll.dll"
...

Steps to be taken in code are the following:

1. Obtain process handle with usual call to OpenProcess function.
2. Read PROCESS_BASIC_INFORMATION structure with call to NtWow64QueryInformationProcess64.
3. Get address of PEB which is present in PROCESS_BASIC_INFORMATION structure.
4. Read PEB structure with call to NtWow64ReadVirtualMemory64.
5. Get address of PEB_LDR_DATA structure.
6. Read PEB_LDR_DATA structure and get address of first LDR_DATA_TABLE_ENTRY element.
7. Keep on reading memory for LDR_DATA_TABLE_ENTRY element while the address of the next element is not equal to the address of the first element.

At step 7 we also read buffer of UNICODE_STRING (which resides in LDR_DATA_TABLE_ENTRY) to obtain current module name.

The code is provided below. It consists of two files, main.cpp and os_structs.hpp.

main.cpp:

#include "os_structs.hpp"

#include <algorithm>
#include <codecvt>
#include <cstdint>
#include <iostream>
#include <stdexcept>
#include <string>
#include <vector>

#ifndef WIN32
#   error "This application must be built as an x86 executable"
#endif

#define GET_FUNC_ADDR(name) _##name name = (_##name)::GetProcAddress(::GetModuleHandleA("ntdll.dll"), #name)

#define IS_TRUE(clause, msg) if (!(clause)) { throw std::runtime_error(msg); }

namespace
{

struct close_on_exit
{
    close_on_exit(HANDLE ptr)
        : ptr_(ptr)
    { };

    ~close_on_exit()
    {
        if (ptr_)
        {
            ::CloseHandle(ptr_);
            ptr_ = nullptr;
        }
    }

private:
    HANDLE ptr_;
};

// Names of modules 
std::string convert_unicode_to_utf8(std::vector<uint8_t> &raw_bytes)
{
    std::vector<uint16_t> unicode(raw_bytes.size() >> 1, 0);
    memcpy(unicode.data(), raw_bytes.data(), raw_bytes.size());

    std::wstring_convert<std::codecvt_utf8<wchar_t>> converter;

    const std::wstring wide_string(unicode.begin(), unicode.end());
    const std::string utf8_string = converter.to_bytes(wide_string);

    return utf8_string;
}

void *get_handle(uint32_t id)
{
    HANDLE handle = ::OpenProcess(PROCESS_ALL_ACCESS, FALSE, id);

    std::cout << "Opening target process...";

    IS_TRUE(NULL != handle, "OpenProcess failed");

    std::cout << " ok" << std::endl;

    return handle;
}

void check_if_process_is_x64(HANDLE handle)
{
    BOOL is_wow64_process = TRUE;
    IS_TRUE(::IsWow64Process(handle, &is_wow64_process), "IsWow64Process failed");
    IS_TRUE(FALSE == is_wow64_process, "Target process is not x64 one");
}

std::vector<uint8_t> read_mem(HANDLE handle, uint64_t address, uint32_t length)
{
    IS_TRUE(handle, "No process handle obtained");

    std::vector<uint8_t> data(length, 0);

    GET_FUNC_ADDR(NtWow64ReadVirtualMemory64);

    NTSTATUS status = NtWow64ReadVirtualMemory64(handle, address, data.data(), data.size(), FALSE);

    IS_TRUE(NT_SUCCESS(status), "NtWow64ReadVirtualMemory64 failed");

    return data;
}

void read_pbi(HANDLE handle, sys::PROCESS_BASIC_INFORMATION64 &pbi)
{
    IS_TRUE(handle, "No process handle obtained");

    GET_FUNC_ADDR(NtWow64QueryInformationProcess64);

    NTSTATUS status = NtWow64QueryInformationProcess64(handle, sys::ProcessBasicInformation, &pbi, sizeof(pbi), NULL);

    IS_TRUE(NT_SUCCESS(status), "NtQueryInformationProcess failed");
}

std::vector<uint8_t> read_peb_data(HANDLE handle)
{
    sys::PROCESS_BASIC_INFORMATION64 pbi = { 0 };
    read_pbi(handle, pbi);

    return read_mem(handle, pbi.PebBaseAddress, sizeof(sys::PEB64));
}

bool get_modules_load_order_via_peb(HANDLE handle)
{
    std::cout << "Getting module load order...\n" << std::endl;

    std::vector<uint8_t> read_peb = read_peb_data(handle);
    sys::PEB64 *peb = (sys::PEB64 *)read_peb.data();

    // ------------------------------------------------------------------------
    // Read memory from pointer to loader data structures.
    // ------------------------------------------------------------------------
    std::vector<uint8_t> read_peb_ldr_data = read_mem(handle, (uintptr_t)peb->LoaderData, sizeof(sys::PEB_LDR_DATA64));
    sys::PEB_LDR_DATA64 *peb_ldr_data = (sys::PEB_LDR_DATA64 *)read_peb_ldr_data.data();
    sys::PEB_LDR_DATA64 *loader_data = (sys::PEB_LDR_DATA64 *)peb->LoaderData;

    const uintptr_t addr_of_ptr_to_first_ldr_module = (uintptr_t)loader_data
        + ((uintptr_t)&loader_data->InLoadOrderModuleList - (uintptr_t)&loader_data->Length);

    ULONGLONG address = peb_ldr_data->InLoadOrderModuleList.Flink;

    uint32_t counter = 1;

    // ------------------------------------------------------------------------
    // Traversing loader data structures.
    // ------------------------------------------------------------------------
    do
    {
        std::vector<uint8_t> read_ldr_table_entry = read_mem(handle, address, sizeof(sys::LDR_DATA_TABLE_ENTRY64));

        sys::LDR_DATA_TABLE_ENTRY64 *ldr_table_entry = (sys::LDR_DATA_TABLE_ENTRY64 *)read_ldr_table_entry.data();

        std::vector<uint8_t> unicode_name = read_mem(handle, ldr_table_entry->BaseDllName.Buffer, ldr_table_entry->BaseDllName.MaximumLength);
        std::string name = convert_unicode_to_utf8(unicode_name);

        std::cout << "Module: " << name << std::endl;
        std::cout << "  Image base: 0x" << std::hex << ldr_table_entry->BaseAddress << std::endl;

        ldr_table_entry = (sys::LDR_DATA_TABLE_ENTRY64 *)read_ldr_table_entry.data();
        address = (uintptr_t)ldr_table_entry->InLoadOrderModuleList.Flink;
    } while (addr_of_ptr_to_first_ldr_module != address);

    std::cout << "\nEnumeration finished" << std::endl;

    return true;
}

}  // namespace

int main()
{
    try
    {
        HANDLE handle = get_handle(16944);
        close_on_exit auto_close_handle(handle);

        check_if_process_is_x64(handle);
        get_modules_load_order_via_peb(handle);
    }
    catch (const std::runtime_error &e)
    {
        std::cerr << "\n----------------------------------------------------\n";
        std::cerr << "Exception occurred: " << e.what();
        std::cerr << "\n----------------------------------------------------\n";
    }

    return 0;
}

os_structs.hpp:

#pragma once

#include <windows.h>

#define NT_SUCCESS(x) ((x) >= 0)

// Namespace is present Not to collide with "winbase.h"
// definition of PROCESS_INFORMATION_CLASS and others.
namespace sys
{

typedef enum _PROCESS_INFORMATION_CLASS {
    ProcessBasicInformation,
    ProcessQuotaLimits,
    ProcessIoCounters,
    ProcessVmCounters,
    ProcessTimes,
    ProcessBasePriority,
    ProcessRaisePriority,
    ProcessDebugPort,
    ProcessExceptionPort,
    ProcessAccessToken,
    ProcessLdtInformation,
    ProcessLdtSize,
    ProcessDefaultHardErrorMode,
    ProcessIoPortHandlers,
    ProcessPooledUsageAndLimits,
    ProcessWorkingSetWatch,
    ProcessUserModeIOPL,
    ProcessEnableAlignmentFaultFixup,
    ProcessPriorityClass,
    ProcessWx86Information,
    ProcessHandleCount,
    ProcessAffinityMask,
    ProcessPriorityBoost,
    MaxProcessInfoClass
} PROCESS_INFORMATION_CLASS, *PPROCESS_INFORMATION_CLASS;

// ------------------------------------------------------------------------
// Structs.
// ------------------------------------------------------------------------

typedef struct _PROCESS_BASIC_INFORMATION64 {
    ULONGLONG Reserved1;
    ULONGLONG PebBaseAddress;
    ULONGLONG Reserved2[2];
    ULONGLONG UniqueProcessId;
    ULONGLONG Reserved3;
} PROCESS_BASIC_INFORMATION64;

typedef struct _PEB_LDR_DATA64 {
    ULONG Length;
    BOOLEAN Initialized;
    ULONGLONG SsHandle;
    LIST_ENTRY64 InLoadOrderModuleList;
    LIST_ENTRY64 InMemoryOrderModuleList;
    LIST_ENTRY64 InInitializationOrderModuleList;
} PEB_LDR_DATA64, *PPEB_LDR_DATA64;

// Structure is cut down to ProcessHeap.
typedef struct _PEB64 {
    BOOLEAN InheritedAddressSpace;
    BOOLEAN ReadImageFileExecOptions;
    BOOLEAN BeingDebugged;
    BOOLEAN Spare;
    ULONGLONG Mutant;
    ULONGLONG ImageBaseAddress;
    ULONGLONG LoaderData;
    ULONGLONG ProcessParameters;
    ULONGLONG SubSystemData;
    ULONGLONG ProcessHeap;
} PEB64;

typedef struct _UNICODE_STRING64 {
    USHORT Length;
    USHORT MaximumLength;
    ULONGLONG Buffer;
} UNICODE_STRING64;

typedef struct _LDR_DATA_TABLE_ENTRY64 {
    LIST_ENTRY64 InLoadOrderModuleList;
    LIST_ENTRY64 InMemoryOrderModuleList;
    LIST_ENTRY64 InInitializationOrderModuleList;
    ULONGLONG BaseAddress;
    ULONGLONG EntryPoint;
    DWORD64 SizeOfImage;
    UNICODE_STRING64 FullDllName;
    UNICODE_STRING64 BaseDllName;
    ULONG Flags;
    SHORT LoadCount;
    SHORT TlsIndex;
    LIST_ENTRY64 HashTableEntry;
    ULONGLONG TimeDateStamp;
} LDR_DATA_TABLE_ENTRY64, *PLDR_DATA_TABLE_ENTRY64;

}  // namespace sys

// ------------------------------------------------------------------------
// Function prototypes.
// ------------------------------------------------------------------------

typedef NTSTATUS(NTAPI *_NtWow64QueryInformationProcess64)(
    IN HANDLE ProcessHandle,
    ULONG ProcessInformationClass,
    OUT PVOID ProcessInformation,
    IN ULONG ProcessInformationLength,
    OUT PULONG ReturnLength OPTIONAL);

typedef NTSTATUS(NTAPI *_NtWow64ReadVirtualMemory64)(
    IN HANDLE ProcessHandle,
    IN DWORD64 BaseAddress,
    OUT PVOID Buffer,
    IN ULONG64 Size,
    OUT PDWORD64 NumberOfBytesRead);

If you're interested in initial structure definitions - the best way I've figured out is to download symbols for WinDbg and then watch structures' layout in this debugger. You can see the sample in this post above.

Answer 3

Use Windows Management Instrumentation (WMI). Example (Delphi):

function GetProcessCount(const aFileName: string): Integer;
var
  lValue: LongWord;
  lWMIService: OleVariant;
  lWMIItems: OleVariant;
  lWMIItem: OleVariant;
  lWMIEnum: IEnumVariant;
begin
  Result := -1;
  lWMIService := GetWMIObject('winmgmts:\\.\root\CIMV2'); { Do not localize. }
  if (TVarData(lWMIService).VType = varDispatch) and (TVarData(lWMIService).VDispatch <> nil) then
  begin
    Result := 0;
    lWMIItems := lWMIService.ExecQuery(Format('SELECT * FROM Win32_Process WHERE Name=''%s''', [ExtractFileName(aFileName)])); { Do not localize. }
    lWMIEnum := IUnknown(lWMIItems._NewEnum) as IEnumVariant;
    while lWMIEnum.Next(1, lWMIItem, lValue) = 0 do
    begin
      Inc(Result);
    end;
  end;
end;