How can a 64-bit process have a 32-bit view of file system and registry?

Question

For backwards compatibility, my 64 process needs to see the the 32-bit view of the file system and registry.

I know how to make a 32-bit process see a 64-bit view of the file system and registry (using Wow64DisableWow64FsRedirection and Wow64RevertWow64FsRedirection)

But how do I make a 64 bit process have a 32 bit view of the file system and registry?

Answer 1

You need to explicitly look in the "WOW64" keys/directories. There is actually no "64-bit" registry, there's just "the registry" and the Wow64 redirection stuff simply redirects a 32-bit process to a different subkey. So when a 32-bit process asks for "HKLM\Software\foo" the registry API actually says, "hang on, you're 32-bit so I'm going to pretend you asked for 'HKLM\Software\Wow6432Node\foo' instead".

So with that in mind, there is no way to have a 64-bit process look in the "32-bit" registry, because there is no such thing as a "32-bit registry". Instead, you'll just have to do what the Wow64 redirection logic does automatically.

EDIT

For the registry, there's actually the KEY_WOW64_32KEY key which you can specify in various method calls.

For the filesystem, you might be able to try Wow64EnableWow64FsRedirection, but I'm not sure whether it'll work or not...

Answer 2

If you want to see the 32-bit registry you can use the KEY_WOW64_32KEY as described here

If you want to access the SysWOW64 directory you can use the GetSystemWow64Directory as described here

Answer 3

KEY_WOW64_32KEY works for 64 bit and 32 bit processes.

From experiment, Wow64EnableWow64FsRedirection/Wow64DisableWow64FsRedirection doesn't seem to work in a 64 bit process - and the name suggests it only seems to work in an WOW64 process.

So in order to have a 32 bit "view" of the file system from a 64 bit process the paths will need to be be altered to point to the correct locations

This is really ugly, but here is a c++ code sample of how to perform the file system redirection according to Microsoft. Requires Boost.

#include"boost/filesystem.hpp"
#include"wstring"
#include"shfolder.h"
#include"Shlobj.h"
bool redirectPathRoot( boost::filesystem::wpath pathFromRoot, boost::filesystem::wpath pathToRoot, boost::filesystem::wpath & pathToRedirect )
{
bool bPathWasRedirected = false;
boost::filesystem::wpath theNewPath;
boost::filesystem::wpath::iterator iPathToRedirect = pathToRedirect.begin();
boost::filesystem::wpath::iterator iFromRoot = pathFromRoot.begin();
bool bMatch = true;
while( iPathToRedirect != pathToRedirect.end() && iFromRoot != pathFromRoot.end() && bMatch )
{
    //
    // see if the root of the path we are checking matches 
    //
    bMatch = ( std::wstring(*iPathToRedirect++) == std::wstring(*iFromRoot++) );
}
if( bMatch && iFromRoot == pathFromRoot.end() )
{
    theNewPath = pathToRoot;
    //
    // these guys need to be redirected
    //
    while( iPathToRedirect != pathToRedirect.end() )
    {
        theNewPath /= *iPathToRedirect++;
    }
    bPathWasRedirected = true;
    pathToRedirect = theNewPath;
}
return bPathWasRedirected;
}
std::wstring adjustPathFor32BitOn64BitProcess( LPCWSTR thePath )
{
std::wstring strPath(thePath);
boost::to_lower(strPath);
//
// default to the original path
//
boost::filesystem::wpath theNewPath(strPath.c_str());
theNewPath.normalize();
//
// init the supplied path
//
boost::filesystem::wpath pathToCheck( strPath.c_str() );
pathToCheck.normalize();
//
// get the path for the 32 bit folder on a 64 bit system
//
wchar_t strTemp[MAX_PATH] = L"\0";
GetSystemWow64Directory( strTemp, MAX_PATH );
std::wstring strSysWow64 = strTemp;
boost::to_lower( strSysWow64 );
boost::filesystem::wpath pathSysWow64( strSysWow64.c_str() );
pathSysWow64.normalize();

//
// get the path for the system directory
//
GetSystemDirectory( strTemp, MAX_PATH );
std::wstring strSys = strTemp;
boost::to_lower( strSys );
boost::filesystem::wpath pathSys( strSys.c_str() );
pathSys.normalize();

//
// get the path for the Program Files directory
//
SHGetFolderPath( NULL, CSIDL_PROGRAM_FILES, NULL, SHGFP_TYPE_DEFAULT, strTemp);
std::wstring strPrograms = strTemp;
boost::to_lower( strPrograms );
boost::filesystem::wpath pathPrograms( strPrograms.c_str() );
pathPrograms.normalize();

//
// get the path for the Program Files x86 directory
//
SHGetFolderPath( NULL, CSIDL_PROGRAM_FILESX86, NULL, SHGFP_TYPE_DEFAULT, strTemp);
std::wstring strProgramsX86 = strTemp;
boost::to_lower( strProgramsX86 );
boost::filesystem::wpath pathProgramsX86( strProgramsX86.c_str() );
pathProgramsX86.normalize();

//
// get the path for the Windows\lastgood\system32 directory
//
SHGetFolderPath( NULL, CSIDL_WINDOWS, NULL, SHGFP_TYPE_DEFAULT, strTemp);
std::wstring strWindows = strTemp;
boost::to_lower( strWindows );
boost::filesystem::wpath pathWindows( strWindows.c_str() );
pathWindows.normalize();

boost::filesystem::wpath pathWindowsLastGoodSystem32( strWindows.c_str() );
pathWindowsLastGoodSystem32 /= L"lastgood";
pathWindowsLastGoodSystem32 /= L"system32";
pathWindowsLastGoodSystem32.normalize();

boost::filesystem::wpath pathWindowsLastGoodSysWOW64( strWindows.c_str() );
pathWindowsLastGoodSysWOW64 /= L"lastgood";
pathWindowsLastGoodSysWOW64 /= L"syswow64";
pathWindowsLastGoodSysWOW64.normalize();


//
// finally, regedit...
//
boost::filesystem::wpath pathRegedit( strWindows.c_str() );
pathRegedit /= L"regedit.exe";
pathRegedit.normalize();

boost::filesystem::wpath pathRegeditSysWOW64( pathSysWow64 );
pathRegeditSysWOW64 /= L"regedit.exe";
pathRegeditSysWOW64.normalize();

//
// now see if the supplied path matches system directoy
//
boost::filesystem::wpath::iterator iPathToCheck = pathToCheck.begin();
boost::filesystem::wpath::iterator iSys = pathSys.begin();
bool bMatch = true;
while( iPathToCheck != pathToCheck.end() && iSys != pathSys.end() && bMatch )
{
    //
    // see if the beginning of the path we are checking matches the system path
    //
    bMatch = ( std::wstring(*iPathToCheck++) == std::wstring(*iSys++) );
}
if( bMatch && iSys == pathSys.end() )
{
    //
    // the supplied path matches at least as far as the system dir...
    //
    if( iPathToCheck == pathToCheck.end() )
    {
        //
        // ...actually its an exact match, so redirect it
        //
        theNewPath = pathSysWow64;
    }
    else
    {
        //
        // ...however, there are a few exceptions....
        //
        boost::filesystem::wpath::iterator iTemp = iPathToCheck;
        if( 
                !(
                    std::wstring(*iTemp) == L"drivers" && 
                    ( 
                        (++iTemp) != pathToCheck.end()  && 
                        std::wstring(*(iTemp)) == L"etc" 
                        )
                    ) 
                &&
                (std::wstring(*iPathToCheck) != L"catroot") &&
                (std::wstring(*iPathToCheck) != L"catroot2") &&
                (std::wstring(*iPathToCheck) != L"logfiles") &&
                (std::wstring(*iPathToCheck) != L"spool")
                )
        {
            //
            // all but the above dirs should be redirected
            //
            theNewPath = pathSysWow64;
            while( iPathToCheck != pathToCheck.end() )
            {
                theNewPath /= *iPathToCheck++;
            }
        }
    }
}
else
{
    //
    // didn't match the system dir... see if it matches the Program Files dir
    //
    if(!redirectPathRoot(  pathPrograms, pathProgramsX86, theNewPath ))
    {
        //
        // now try %windir%/lastgood/system32
        //
        if(!redirectPathRoot(  pathWindowsLastGoodSystem32, pathWindowsLastGoodSysWOW64, theNewPath ))
        {
            //
            // finally, regedit
            //
            redirectPathRoot(  pathRegedit, pathRegeditSysWOW64, theNewPath );
        }
    }

}
return theNewPath.file_string();}

Answer 4

Bit late to the party, but could you not create a small 32-bit process that does your 32-bit work? Then all of the built in goodness of WOW64 will work.

Not sure what your development language/runtime is like, so not able to offer further suggestions on what the inter-process communication would look like.