Question

Since the release of Win Vista, Microsoft introduced file virtualization for legacy applications running as 32bit processes. Released as part of Microsoft’s User Account Control (UAC) any legacy applications attempting to write to any locations considered protected by the operating system are redirected to the VirtualStore.

At this point, steps have been taken to ensure that the application in question now runs as a 64bit process that is UAC aware, however, this does little to address the issue of migrating the users data to a location that is considered safe from virtualization.

While troubleshooting this issue, I’ve found that when dealing with multiple user accounts some changes have been made within the legacy path located at C:\Program Files(x86)\MyApp\Data while at the same time, changes have been made to the VirtualStore located at %localappdata%\VirtualStore\Programs\MyApp\Data. The question being, how can I detect if any file/folder virtualization is taking place and how can I merge the two locations?

EDIT: I found several websites that detail the problem and how to duplicate it, but nothing that includes a way to fix it. I did find this reference FILE_ATTRIBUTE_VIRTUAL that defines a file attribute that seems promising – I found another reference somewhere, though I can’t remember where, that states that this is the attribute used by Windows to indicate that file virtualization is taking place and flags the request for redirection.

These links describe the issue:

http://www.c-sharpcorner.com/uploadfile/GemingLeader/windows-file-and-registry-virtualization/

http://www.codeproject.com/Articles/66275/Windows-Vista-File-and-Registry-Virtualization

http://download.microsoftvirtuallabs.com/download/8/a/7/8a71365b-4c80-4e60-8185-8f12f59bf1d4/UACDataRedirection.pdf

Answer 1

Wasn’t easy, but I found how to detect whether UAC virtualization is enabled. Calling GetTokenInformation() and passing in TokenVirtualizationEnabled as the information class will return whether file and registry virtualization is enabled. Here is a C function to do it:

// Gets whether the current process has UAC virtualization enabled.
// Returns TRUE on success and FALSE on failure.
BOOL GetVirtualizationEnabled(BOOL *enabled) {
    HANDLE token;
    DWORD tmpEnabled;
    DWORD returnLen;
    BOOL retVal = TRUE;

    if(!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &token))
        return FALSE;

    if(!GetTokenInformation(token, TokenVirtualizationEnabled,
            &tmpEnabled, sizeof(tmpEnabled), &returnLen)) {
        retVal = FALSE;
        goto err;
    }

    *enabled = tmpEnabled;

err:
    CloseHandle(token);

    return retVal;
}

A bit harder with P/Invoke, but here it is, including the P/Invoke headers:

enum TOKEN_INFORMATION_CLASS
{
    TokenUser = 1,
    TokenGroups,
    TokenPrivileges,
    TokenOwner,
    TokenPrimaryGroup,
    TokenDefaultDacl,
    TokenSource,
    TokenType,
    TokenImpersonationLevel,
    TokenStatistics,
    TokenRestrictedSids,
    TokenSessionId,
    TokenGroupsAndPrivileges,
    TokenSessionReference,
    TokenSandBoxInert,
    TokenAuditPolicy,
    TokenOrigin,
    TokenElevationType,
    TokenLinkedToken,
    TokenElevation,
    TokenHasRestrictions,
    TokenAccessInformation,
    TokenVirtualizationAllowed,
    TokenVirtualizationEnabled,
    TokenIntegrityLevel,
    TokenUIAccess,
    TokenMandatoryPolicy,
    TokenLogonSid,
    MaxTokenInfoClass
}

public const UInt32 STANDARD_RIGHTS_REQUIRED = 0x000F0000;
public const UInt32 STANDARD_RIGHTS_READ = 0x00020000;
public const UInt32 TOKEN_ASSIGN_PRIMARY = 0x0001;
public const UInt32 TOKEN_DUPLICATE = 0x0002;
public const UInt32 TOKEN_IMPERSONATE = 0x0004;
public const UInt32 TOKEN_QUERY = 0x0008;
public const UInt32 TOKEN_QUERY_SOURCE = 0x0010;
public const UInt32 TOKEN_ADJUST_PRIVILEGES = 0x0020;
public const UInt32 TOKEN_ADJUST_GROUPS = 0x0040;
public const UInt32 TOKEN_ADJUST_DEFAULT = 0x0080;
public const UInt32 TOKEN_ADJUST_SESSIONID = 0x0100;
public const UInt32 TOKEN_READ = (STANDARD_RIGHTS_READ | TOKEN_QUERY);
public const UInt32 TOKEN_ALL_ACCESS = (STANDARD_RIGHTS_REQUIRED | TOKEN_ASSIGN_PRIMARY |
    TOKEN_DUPLICATE | TOKEN_IMPERSONATE | TOKEN_QUERY | TOKEN_QUERY_SOURCE |
    TOKEN_ADJUST_PRIVILEGES | TOKEN_ADJUST_GROUPS | TOKEN_ADJUST_DEFAULT |
    TOKEN_ADJUST_SESSIONID);

[DllImport("advapi32.dll", SetLastError=true)]
static extern bool GetTokenInformation(
    IntPtr TokenHandle,
    TOKEN_INFORMATION_CLASS TokenInformationClass,
    IntPtr TokenInformation,
    int TokenInformationLength,
    out uint ReturnLength);

[DllImport("advapi32.dll", SetLastError = true)]
static extern bool SetTokenInformation(IntPtr TokenHandle, TOKEN_INFORMATION_CLASS TokenInformationClass,
    ref uint TokenInformation, uint TokenInformationLength);

[DllImport("advapi32.dll", SetLastError=true)]
static extern bool OpenProcessToken(IntPtr ProcessHandle,
    uint DesiredAccess, out IntPtr TokenHandle);

[DllImport("kernel32.dll", SetLastError=true)]
    static extern bool CloseHandle(IntPtr hObject);

static bool TryGetVirtualizationEnabled(out bool enabled) {
    IntPtr processHandle = Process.GetCurrentProcess().Handle;
    IntPtr token;
    uint returnLen;
    object tmpEnabled = new uint();

    enabled = false;
    GCHandle handle = GCHandle.Alloc(tmpEnabled, GCHandleType.Pinned);

    try {
        if(!OpenProcessToken(processHandle, TOKEN_QUERY, out token))
            return false;

        try {
            if(!GetTokenInformation(token, TOKEN_INFORMATION_CLASS.TokenVirtualizationEnabled,
                                    handle.AddrOfPinnedObject(), Marshal.SizeOf(typeof(uint)), out returnLen))
                return false;

            enabled = (uint)tmpEnabled != 0;
        } finally {
            CloseHandle(token);
        }
    } finally {
        handle.Free();
    }

    return true;
}

I tried turning UAC virtualization on and off with Task Manager and verified that the correct result is returned. Enabling and disabling virtualization can be done by calling SetTokenInformation().

Microsoft says they plan on removing UAC virtualization in a future Windows version and for programs to not rely on it existing. I saw a suggestion by someone to make a separate program that is not UAC aware to move files from the VirtualStore to AppData, but I don’t know if that’s a good solution or not.