Modifying a Visual C++ 2010 project’s Platform Toolset programmatically with IVCRulePropertyStorage

Back from a long hiatus.

Lately I’ve been migrating a large legacy code base from Visual C++ 2008 to Visual C++ 2010. Visual C++ 2010 supports Native Multi-Targeting, which lets you use the Visual Studio 2010 IDE and the new MSBuild-based C++ project system (*.vcxproj files, etc.) while invoking a legacy compiler like Visual C++ 2008 for the actual build, or for invoking the modern compiler with special INCLUDE and LIB directory settings (e.g., using the Windows Driver Kit’s headers and import libraries).

The “Platform Toolset” is the project setting which specifies which baseline compiler settings apply. Visual Studio 2010 bundles the “v100” platform toolset for using the Visual C++ 2010 compiler and the “v90” platform toolset for using the Visual C++ 2008 compiler. The Windows SDK 7.1 includes the “Windows7.1SDK” platform toolset which invokes the Visual C++ 2010 compiler, but with the SDK’s build environment. The latest Intel C++ Compiler includes a “Intel C++ Compiler XE 12.0” toolset, as well. A third party has even created a platform toolset for the antiquated Visual C++ 2003 compiler.

The IDE GUI exposes the Platform Toolset project setting in the General property sheet. By right clicking a project in Solution Explorer, clicking Properties and going to General under Configuration Properties, you can change the setting on a per-build configuration basis. Solution Explorer is clever enough to let you group select several or all of the projects in the open solution and group-modifying the platform toolset in the properties dialog. For many cases, this may be sufficient.

However, if you want to modify the platform toolset en masse, but based on more complicated criteria, or just wish to achieve a higher degree of automation in the migration process, you may prefer to modify the setting programmatically like I did.

Visual Studio has an automation model for modifying project settings and for many other IDE tasks. This object model is accessible from Visual Studio Macros (which have unfortunately been removed from the Visual Studio 11 Developer Preview) and from other forms of Visual Studio extensibility such as add-ins. After some browsing of the documentation and searching the Web, it is clear how to modify things like the project’s Linker OutputFile property. However, it took me a while to figure out how to access other properties like the PlatformToolset.

It turns out that project settings that have appeared recently are not accessible in straightforward way like the older ones. That is, they are not properties of the VCProject object or its child objects. Instead, there is a new interface for manipulating these properties, IVCRulePropertyStorage.

With this interface, the PlatformToolset property in the General property sheet becomes easily accessible. To illustrate, the following is an example Visual Studio macro that changes the platform toolset of any project in the solution using the “v100” toolset to the “Windows7.1SDK” toolset:

Option Strict On
Option Explicit On

Imports System
Imports EnvDTE
Imports EnvDTE80
Imports EnvDTE90
Imports EnvDTE90a
Imports EnvDTE100
Imports System.Diagnostics
Imports Microsoft.VisualStudio.VCProject
Imports Microsoft.VisualStudio.VCProjectEngine

Public Module Module1
Sub RetargetProjects()
  For Each p As Project In DTE.Solution.Projects
    If p.Kind = vcContextGuids.vcContextGuidVCProject Then
      Dim prj As VCProject = CType(p.Object, VCProject)

      For Each cfg As VCConfiguration In CType(prj.Configurations, IVCCollection)
        Dim generalRule As IVCRulePropertyStorage = CType(cfg.Rules.Item("ConfigurationGeneral"), IVCRulePropertyStorage)

        Dim currentPlatformToolset = generalRule.GetUnevaluatedPropertyValue("PlatformToolset")

        If currentPlatformToolset = "v100" Then
          generalRule.SetPropertyValue("PlatformToolset", "Windows7.1SDK")
        End If
    End If
End Sub
End Module

You need to add references to the VCProject and VCProjectEngine assemblies in your macro project to access the types of the Visual C++ Project Model used in this macro.

Stay tuned for more useful functionality of IVCRulePropertyStorage.

Visual Studio 2010 Beta 2 debugger may be confused by your symbol path

I’ve been evaluating Microsoft’s Visual Studio 2010 Beta 2 release recently on my Windows 7 x64 system. As can be expected, the beta has quite a few rough edges, but overall I like the new WPF-based IDE GUI and the refreshed code Editor in particular (I like how selecting a block of code now preserves syntax highlighting while the block is highlighted, for instance).

The new GUI does have some badness. I had particular distaste for the poor aliasing of tooltips in the editor. This can be seen, for example, when hovering over a function name like “printf”. The menu bar’s dark blue color scheme also appears rather peculiar.

Besides the “bling”, notable changes include the Visual C++ 2010 CRT reverting to the traditional deployment model used by the Visual C++ 2003 CRT. More specifically, the CRT DLLs no longer use SxS binding (“Fusion”) and are now simply deployed to the “system32” directory or to the application’s directory, as desired. Dropping SxS has some obvious disadvantages (SxS binding redirects would no longer be able to redirect applications that load a private copy of the CRT DLLs to updated versions with bug fixes and security updates) but presumably the pain of integrating SxS deployment into the setup process, which required either an MSI installation or pseudo-documented use of the SxS API, resulted in too much negative feedback and they chose to revert to the legacy approach.

Visual C++ projects are now built with MSBuild, like their C# and other .NET counterparts. This should have several benefits. One that comes to mind is the the Windows Installer XML Toolset’s Votive (its VS IDE integration component) should be able to support C++ projects as References in addition to .NET projects.

A more important update to the project system is support for multi-targeting. Most of Microsoft’s discussions on the subject mainly deal with said support for .NET projects, with the new Visual Studio being able to target .NET 2.0 through .NET 4.0 on a per-project basis. However, similar support is offered for native multi-targeting. A per-project setting specifies the “toolset” with which it is to be built. The product comes built-in with toolset definitions for the VC++ 10 and the VC++ 9 compilers, but since toolset definitions are simple XML files describing tool paths, older compilers and custom definitions are easy to define. Indeed, a toolset definition can be found for the Windows 7 SDK build environment. I foresee using this functionality to build user-space applications with headers and tools from the Windows Driver Kit build environment, resulting in being able to link with the OS CRT (msvcrt.dll) in a clean way, without modifying global Visual C++ directory settings, but rather keeping the changes contained to specific projects.

My enthusiasm for testing the product was struck a severe blow when my first attempt to run the Visual C++ debugger on a “Hello, World!” console application went awry. The IDE was hung for a good 15-20 seconds. The IDE sat frozen for quite a bit after F10 was pressed to initiate the debugging session, finally presented the console window for the test application and then spent some more time being frozen. After a lengthy wait, the session was finally ready.

But the worst part was that when the debugging session was finally ready, debugging symbols for all modules except the application .exe and the VC 10 CRT were NOT loaded! It appeared as though the lengthy wait was all for naught.

The experience was sufficiently poor for me to report it to Microsoft through one of the feedback channels. I was eventually contacted by helpful folks from the Visual Studio Debugger team and we analyzed the problem in an e-mail exchange. The performance issue is the result of problematic contents of the symbol path I configured for the debugger.

As I mentioned, I’m evaluating the beta on a Windows 7 machine. For this reason, the Windows 7 symbol packages, available from Microsoft’s public symbols download page, are deployed in my system and are a part of the symbol path defined by the _NT_SYMBOL_PATH environment variable. Since this is an x64 machine and I find myself debugging 32-bit processes quite often, both the 32-bit and 64-bit symbol packages are installed. My initial symbol path was:


The first issue with this symbol path is that the x64 symbols package (extracted to C:\Symbols) and the x86 symbols package (extracted to C:\Symbols32) are specified as directories in the symbol path, rather than symbol stores. This is what you’d expect from symbol packages designed for local deployment, but it turns out that the Windows 7 symbol packages, unlike the PDB packages for previous versions of Windows, come in the symbol store directory layout rather than the flat directory layout. This means, for example, that the symbols for ntdll.dll are in a path like C:\Symbols\ntdll.pdb\CFF40300FD804691B73E12CF2A150EE02\ntdll.pdb rather than the simpler C:\Symbols\dll\ntdll.pdb.

I did not notice this issue, however, before installing Visual Studio 2010 Beta 2, because apparently Windbg doesn’t mind when stores are specified in this syntax, as it exercises some sort of heuristic to determine the layout of a symbol directory. However, Visual Studio 2010 Beta 2 is not as liberal. Examining its I/Os with Sysinternals Process Monitor determined that it wasn’t trying to find PDBs under the symbol directories except directly under them or in a “dll” subdirectory, rather than looking for the appropriate hash as it would in a symbol store. The resolution for this issue is simple enough, refer to the Windows 7 symbol packages with SRV* syntax in the symbol path. Therefore, the symbol path is updated to something like:


With this change in place, the Visual Studio 2010 Beta 2 debugger was able to pick up symbols for system DLLs from the local stores, and now the debugging session started instantly. But the question remained: even if the debugger didn’t know how to look for symbols under C:\Symbols and C:\Symbols32 when they were not specified with a srv* directive, why did it download symbols from the HTTP public store, only to end up starting with symbols not being loaded for any of the system DLLs in the debugged process?

To get to the bottom of this, the local symbol caches were removed from the symbol path. At this point, it was


Running the debugger with this stripped down symbol path reproduced the poor debugger startup experience and the worse issue of symbols being downloaded only to end up not being used. At this point, Sysinternals Process Monitor was used to examine the actions of the debugger. Two curious facts were revealed.

The first was that the Visual Studio debugger was literally examining a directory called “cache*C:\websymbols” under its path in a vain attempt to find symbols. Since the “cache*” string made it to a file open request, obviously the cache* directive in the _NT_SYMBOL_PATH variable was not being correctly parsed or understood by the debugger.

The result of this deficiency is that the Visual Studio debugger should be using some default local cache directory for the downloaded symbols, instead of the one explicitly specified by the cache* directive. Therefore, the same behavior would be expected with the following symbol path:


And indeed, a quick check revealed that the same peculiarity reproduced with this symbol path setting: symbols were being downloaded from the HTTP server, but in the end of the process, symbols were not loaded for any of the system modules in the debugged process. Whatever the default directory is, attempts to download symbols there resulted in their loss into oblivion.

Specifying the local symbol cache using the SRV* directive is also possible. This is the legacy approach, before Windbg recommend using CACHE* instead. A symbol path of this form is


With this symbol path in place, the Visual Studio 2010 Beta 2 debugger both downloaded symbols from the HTTP store and actually ended up using them. Specifying the cache directory with CACHE* or not at all triggered the bug, while specifying it the old fashioned way in the SRV* directive satisfied the debugger.

As a result, my guidance for the Visual Studio 2010 Beta 2 debugger users experiencing performance issues or other symbol problems that have no issue with their symbol path when used with Windbg is:

  1. For each directory in your _NT_SYMBOL_PATH, determine whether it is in the “flat” format or in symbol store format. Prefix symbol stores with SRV*, changing “C:\Symbols” to “SRV*C:\Symbols”. Windows 7 users in particular should be aware that the symbol packages for their platforms should be specified with SRV* syntax for Visual Studio 2010 Beta 2.
  2. Specify local caches directories for remote symbol stores (SMB or HTTP) directly in the SRV* directive, to have Visual Studio 2010 Beta 2 pick them up. It is OK to keep the CACHE* directive in your symbol path as well, but for the time being, Visual Studio 2010 Beta 2 does not seem to use it correctly.

The Visual Studio Debugger team is addressing issues revealed by the investigation of this behavior for the forthcoming RTM release of Visual Studio 2010. However, several significant deficiencies in debugger symbol support will not be addressed in the 2010 release. One is that symbol loading is done synchronously rather than asynchronously to the debugging session. The other being that unless manual symbol loading is used, no progress indication nor cancellation UI is presented as the symbols are being transferred from a remote store. Therefore, the perceived performance of symbol support in the debugger will leave something to be desired for the time being.

IDA v5.4 supports Windbg as a debugger backend

A new release of IDA, the Interactive Disassembler, has been recently released featuring new debugger integration capabilities. IDA’s existing built-in debugger often proved lackluster, but IDA’s static analysis and navigation features are, of course, unrivaled by anything else. I always wished IDA would address the weakness of its debugging features and now they have done so in the v5.4 release. The new version can drive a gdb debugging server (as embedded platforms often provide), a Bochs virtual machine (great for BIOS and boot loader debugging) and most importantly DbgEng, the Microsoft debugging engine used by Windbg. Since Windbg sessions often involve heavy use of PDBs, IDA v5.4 has improved its support for importing data from PDBs and now uses more of their embedded type information (previously the third party Determina PDB plugin attempted to improve IDA’s PDB support). To top things off, the Python plugin is now bundled with IDA, as well.

I haven’t had the chance to use the new version yet, but Hex Rays have a great demo video posted here. The only thing notable that appears missing is a nice UI for examining the stack trace, but if push comes to shove the Windbg command line can be used to invoke “k”, as demonstrated.

Windbg released

Version of the Debugging Tools for Windows package has been available for a few days now.

The big news on this one is lots of FireWire debugging changes. An updated host driver is provided and claims of greater reliability and controller compatibility are made. Additional changes include better WOW64 support, claims of performance improvements to the various debuggers in the package (it remains to be seen how significant those are), many improvements to the almighty !analyze extension command and extensive updates to the debugger documentation. Absent from this release is NT 4.0 support. I suppose not many will miss it at this point.

Developers using the debugger API may be interested that symbols for dbghelp.dll v6.10.3.233 are available from the public symbol store, while symbols for dbgeng.dll v6.10.3.233 are once again missing, a sorry tradition of making the debugger interface consumer’s life hard since the 6.8 debugger release, if I recall correctly.

Oops! Microsoft private symbols accidently leaked in Visual Studio 2010 CTP VM image

I downloaded Microsoft’s newly released Visual Studio 2010 CTP virtual machine disk image hoping for a few surprises, but I certainly didn’t expect this…

The Visual Studio 2010 CTP is a huge multi-gigabyte VM running Windows Server 2008. The first thing I did with it is start up Visual C++ 2010, create a Win32 console application and run it in the debugger. I looked at the stack trace and saw the following:

vc10app.exe!wmain(int argc=1, wchar_t * * argv=0x000d1470) Line 8
vc10app.exe!__tmainCRTStartup() Line 564 + 0x19 bytes
vc10app.exe!wmainCRTStartup() Line 392
kernel32.dll!BaseThreadInitThunk(unsigned long RunProcessInit=0, long (void *)* StartAddress=0x00000000, void * Argument=0x7ffdf000) Line 66 + 0x5 bytes
ntdll.dll!__RtlUserThreadStart(long (void *)* StartAddress=0x013b1073, void * Argument=0x7ffdf000) Line 2740
ntdll.dll!_RtlUserThreadStart(long (void *)* StartAddress=0x013b1073, void * Argument=0x7ffdf000) Line 2672 + 0xb bytes

vc10app is the name of my test console application. I go over stack traces on a daily basis so the special thing about this one immediately caught my attention. Notice that the wmain() function of my console application has full debugging information (as expected for something I wrote) and the parameter names argc and argv are visible in the stack trace. Under normal circumstances, only public debugging symbols are available for Microsoft OS components like kernel32 and ntdll. In this CTP VM, however, the StartAddress and Argument parameters were visible as well.

Public debugging symbols are stripped versions of the original private symbols generated by the build process. They do not contain parameter information and do not contain the names of local variables in functions. Note however that for C++ functions, name mangling results in parameter types being visible in public symbols as well. Normally, when running the debugger in a system configured to use Microsoft’s public symbols, names for internal functions are visible in stack traces, but the names of arguments and locals never are.

I opened the Modules tab of the Visual Studio debugger to determine where the debugger is picking up these symbols for kernel32 and ntdll. The debugger was using C:\ppa\symstore as the symbol store. I opened the C:\ppa directory and saw that a Visual Studio Profiler session for a matrix multiplication application was stored there.

Apparently someone with access to Microsoft’s internal symbol store ran a profiling session on this matrix multiplication application, perhaps to ensure profiling is functional on the CTP VM. The private symbols retrieved for the session were persisted in the CTP’s disk and made their way to the public release. To ensure my hypothesis was correct, I installed Windbg on the machine, opened ntdll.dll as a crash dump and loaded symbols from the store directory:

Microsoft (R) Windows Debugger Version 6.9.0003.113 X86
Copyright (c) Microsoft Corporation. All rights reserved.
Loading Dump File [C:\Windows\System32\ntdll.dll]
Symbol search path is: SRV*c:\ppa\symcache;.
Executable search path is:
ModLoad: 77ed0000 77ff7000 C:\Windows\System32\ntdll.dll
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000000 edi=00000000
eip=77ed0000 esp=00000000 ebp=00000000 iopl=0 nv up di pl nz na po nc
cs=0000 ss=0000 ds=0000 es=0000 fs=0000 gs=0000 efl=00000000
77ed0000 4d dec ebp
0:000> .reload /f
Loading unloaded module list
0:000> lm
start end module name
77ed0000 77ff7000 ntdll (private pdb symbols) c:\ppa\symcache\ntdll.pdb\B958B2F91A5A46B889DAFAB4D140CF252\ntdll.pdb
0:000> x ntdll!RtlAllocateHeap
77f358a6 ntdll!RtlAllocateHeap (void *, unsigned long, unsigned long)
0:000> dv /f ntdll!RtlAllocateHeap
@ebp+0x08 HeapHandle
@ebp+0x0c Flags
@ebp+0x10 Size
@ebp+0x08 ExtraSize
@ebp-0x04 AllocationSize
@ebp-0x08 Interceptor
@ebp-0x58 ExceptionRecord

The private PDB for ntdll.dll found in this CTP VM image notes how HeapHandle, Flags, Size and ExtraSize are the parameter names for RtlAllocateHeap. Furthermore, AllocationSize, Interceptor and ExceptionRecord are used as local names in this API.

Private PDBs also feature source information. This is also visible in this case:

0:000> ln ntdll!RtlAllocateHeap
Source Depot: //depot/longhorn_rtm/base/ntos/rtl/heap.c#1
(77f358a6) ntdll!RtlAllocateHeap | (77f35997) ntdll!RtlpLowFragHeapFree
Exact matches:
ntdll!RtlAllocateHeap (void *, unsigned long, unsigned long)

The PDB features references to the source file from the Windows source tree for RtlAllocateHeap and the other APIs. Additionally, it appears to contain a custom reference to Microsoft’s internal source control system, Source Depot, presumably to facilitate the debugger retrieving up to date sources automatically when those are not available locally.

It’s interesting how scattered bits of information in a debugging symbols file provide a fascinating insight into Windows. Hope you enjoyed the surprise as much as I did…

Installing filter drivers with DIFxApp and a WiX v3 MSI

The designers of Windows Installer probably did not have driver installation in mind. Indeed, the ServiceInstall MSI database table does not even allow for service types SERVICE_KERNEL_DRIVER and SERVICE_FILE_SYSTEM_DRIVER in the ServiceType column. Originally, Microsoft encouraged driver installation by means of a “setup application”, custom code invoking the SetupAPI. The Setup API functions would be used to examine an .INF file describing required steps for the driver’s installation. Back in Windows NT 4.0, even .INF files were often avoided in lieu of directly setting up the legacy driver service in the system registry with C code.

Enter Windows 2000 with Plug and Play. Now the system uses .INF files it maintains in a store to locate and install drivers for devices on demand. When a new device is inserted, the system looks for an .INF file with a matching hardware identifier. For most hardware devices, .INF based installation becomes a de-facto requirement. However, for other driver categories, such as file system filters, device class filters, etc., an .INF file is but one way of performing the driver installation process.

Microsoft, when confronted by driver setup authors who denounce .INF files as having cryptic, old-fashioned syntax, non-ideal diagnosibility and debuggability and other shortcomings, persists in encouraging their use. They are a WHQL logo requirement and in some cases it is claimed they will be the only way to install drivers in future Windows releases.

Often driver installation is but a part of the installation process of a larger application program. For applications, Microsoft encourages (and mandates as a logo requirement) the use of MSI packages and the Windows Installer service. In order to avoid having every MSI setup author who needs to perform driver installation roll his own custom invocation of the driver’s .INF installation and in a bid to improve driver installation’s synergy with Windows Installer in general, Microsoft created DIFxApp – Driver Install Frameworks for Applications.

MSI and DIFxApp’s .INF based installation make for an odd couple. The Windows Installer model is transactional – describe what changes should be made to the system and let Windows Installer determine how to execute them and importantly, how to roll them back. After having encouraged COM DLLs to encapsulate the details of their installation and registration with the Self-Registration DllRegisterServer export for years, describing the individual elements of the COM registration using an MSI’s Registry table is now encouraged instead. DllUnregisterServer can fail in mysterious ways due to missing dependencies, etc., leaving cruft behind during uninstallation. By contrast, rolling back insertions made from the Registry table is always possible for the MSI service. If COM’s long standing installation architecture was set aside to better align with MSI’s model, one would expect a similar occurance for drivers. However, DIFxApp, the solution for installing drivers with MSI, is the moral equivalent of COM Self-Registration. If a driver’s .INF does not remove all changes it made during installation, the uninstallation process is bound to be imperfect. MSI’s ability to diagnose whether a driver’s installation has been damaged is limited and thwarted.

Be that as it may, .INF files’ tight integration with the Plug and Play system, the fact they are a logo requirement and uniformity considerations are compelling arguments for their use. From this point forward, it shall be assumed that .INF based installation and MSI integration have been chosen.

If you’ve developed a common PnP WDM driver, you probably already have an .INF for installation purposes. That .INF can usually be used as is with DIFxApp, which assumes PnP drivers by default. It is for other driver categories that the process becomes more tricky. I’ll discuss filter drivers of three varieties in particular – file system filters, file system minifilters and device class filters.

For illustration purposes, let’s consider a typical file system minifilter driver, DirFilter, which is presently a pet project of mine that will eventually perform interesting modifications to directory listing I/O operations. The following is DirFilter’s .INF file:

Signature = "$Windows NT$"
Class = "ActivityMonitor"
ClassGuid = {b86dff51-a31e-4bac-b3cf-e8cfe75c9fc2}
Provider = %Koby%
DriverVer = 09/12/2008,
CatalogFile =
DriverPackageType = FileSystemMinifilter
DefaultDestDir = %DIRID_DRIVERS%
DirFilter.DriverFiles = %DIRID_DRIVERS%
OptionDesc = %ServiceDescription%
CopyFiles = DirFilter.DriverFiles
AddService = %ServiceName%,,DirFilter.Service
DelFiles = DirFilter.DriverFiles
DelService = %ServiceName%,0x200 ;Ensure service is stopped before deleting
DisplayName = %ServiceName%
Description = %ServiceDescription%
ServiceBinary = %12%\%DriverName%.sys ; DIRID_DRIVERS
Dependencies = "FltMgr"
LoadOrderGroup = "FSFilter Activity Monitor"
AddReg = DirFilter.AddRegistry
dirfilter.sys = 1
1 = %DiskId1%
Koby = "Koby Kahane"
ServiceDescription = "DirFilter minifilter driver"
ServiceName = "DirFilter"
DriverName = "DirFilter"
DiskId1 = "DirFilter minifilter installation media"
; Instance specific information.
Instance1.Name = "DirFilter Instance"
Instance1.Altitude = "370021" ; Real world minifilters should use Microsoft allocated altitude
Instance1.Flags = 0x0 ; Allow automatic attachments

This is, I believe, a pretty typical .INF for a minifilter. A default instance of it is set up at an altitude in an appropriate filter load order group. This is as good a place as any to note the importance of requesting a Minifilter Altitude Allocation from Microsoft for public drivers rather than using some random number which may end up causing conflicts and interoperability issues. From my experience, it takes Microsoft two months or so to respond to an allocation request so make sure to take care of it early in your release cycle.

As a first step towards a DIFxApp-based MSI driver installation, write an .INF file that will work when right clicking it and selecting Install from Explorer’s popup menu. This calls SetupAPI’s InstallHinfSection on the .INF file’s DefaultInstall section. Further, ensure that the uninstallation process works as expected, and leaves no trails behind, by using InstallHinfSection to invoke the DefaultUninstall section of the file.

You may discover that you are encountering difficulty at this stage. I recommend running the ChkINF utility, which analyzes .INF files for errors and mishaps, before testing the .INF file and indeed after every modification to an existing file. ChkINF, while sometimes terse, is nowhere near as cryptic as errors you will receive from SetupAPI. However, if you encounter setup errors even after ChkINF has verified your file, you can utilize verbose SetupAPI logging to further diagnose setup issues.

With a working “right-click Install” .INF file, the time is ripe for integration into an MSI installer. First of all, DIFxApp requires an additional directive in the Version section of your .INF file, the DriverPackageType. The driver package type is used by DIFx to determine what steps are required for the installation of your specific type of driver. For example, if you fail to specify the type of your file system filter, DIFx assumes it is a PnP driver and the “installation” will just import the .INF into the system driver store. No service will be created and success will not be achieved. Unfortunately, the documentation for the DriverPackageType is sorely lacking at best. You will see it only mentions ClassFilter and PlugAndPlay as possible types in MSDN. MSDN proves a disappointment. However, another Microsoft information source, their Requirements for Driver Packages that are Used with the DIFx Tools document, calls for the use of DIFx for Class Filters, Plug and Play drivers, File System & File System Filter drivers, Network drivers, Kernel Service Drivers and Export Drivers. The DriverPackageType values ClassFilter, FileSystem, FileSystemFilter, KernelModule, KernelService, Network and PlugAndPlay are documented there. You may notice that a special type for minifilters is conspicuously absent from the list. At first, I figured perhaps DIFx has no need for a distinction between legacy filters and minifilters. Later, an old post (free registration required) on OSR’s NTFSD mailing list turned my attention to the fact DIFx will require a system restart for a minifilter, even though it can be loaded and unloaded without one. Neal Christiansen, Microsoft’s File System Filter Group Lead, replies (back in 2004) that appropriate support for minifilter installation is forthcoming. I therefore set out to discover whether DIFxApp as available today provides special support for minifilters.

When the Windows Server 2008 WDK is installed to the default location, the x86 versions of the DIFxApp MSI custom action DLLs reside in C:\WINDDK\6001.18000\redist\DIFx\DIFxApp\English\WixLib\x86. I examined them with the Interactive Disassembler and was happy to see Microsoft made available public symbols (.PDBs) for them. To make a long story short, the DriverPackageType field is examined by DIFxApp in the SetupAPI::CDriverPackage::GetDriverType(CRefPtr<SetupAPI::CInf>, DRVPKG_TYPE&) function in DIFxAppA.dll, which references a global table, dubbed DriverTypeStringList, for possible package types:

It is now evident that available driver package types as of DIFx 2.1 are ClassCoInstaller, ClassFilter, DeviceFilter, FileSystem, FileSystemFilter, FileSystemMinifilter, KernelModule, KernelService, NdisImMiniport, Network and PlugAndPlay. With this information, I opted for the FileSystemMinifilter type for DirFilter’s installation .INF file.

Next, a catalog file is required by DIFx. Even though the purpose of the catalog is to be WHQL signed by Microsoft, DIFx can be used to install drivers without WHQL certification. Nevertheless, the catalog still needs to be there. The easy way is to use the Inf2Cat tool for the catalog’s generation. Place the .INF file and the driver files it references in a staging area and you can run it like so:

E:\Projects\dirfilter\staging>inf2cat /driver:E:\Projects\dirfilter\staging /os:Server2008_X86,Vista_X86,Server2003_X86,XP_X86,2000 /verbose

Specifying, of course, the operating systems and platforms appropriate for your driver.

An .INF file, a .CAT file and a .SYS file are the three files required for a DIFxApp driver package. The DIFxApp model requires your MSI to install these files to a source directory, per driver package (i.e., if you have multiple drivers, they’ll need multiple .INFs in multiple directories) and performs the installation from there to the Windows driver store and eventually the drivers directory under system32.

Microsoft distributes a WiX library and documentation for using it with DIFxApp. However, that library targets the older WiX v2.0 release. WiX v3.0 is the actively developed version, and has different schema, semantics and a slightly different integration model with DIFxApp. If you use WiX v2.0, consult Microsoft’s documentation. Otherwise, let’s proceed. The following .wxs file is the sample installer I wrote for installing DirFilter with DIFxApp:

<?xml version='1.0' encoding='windows-1252'?>
<Wix xmlns=''
    <Product Name='DirFilterInstaller' Id='59486bf1-77ad-460f-802d-29dbab0f78be' Language='1033' Codepage='1252' Version='1.0' Manufacturer='KK' UpgradeCode='96fe2ba0-fe8b-45b4-85ef-ea9aca103e6f'>
        <Package Id='*' Keywords='DirFilter' Description='DirFilter Installer' Comments='Installs DirFilter' Manufacturer='KK' InstallerVersion='100' Languages='1033' Compressed='yes' SummaryCodepage='1252' />
        <Media Id='1' Cabinet='' EmbedCab='yes' DiskPrompt='DirFilter Media' />
        <Property Id='DiskPrompt' Value='DirFilter Install Media' />
        <Directory Id='TARGETDIR' Name='SourceDir'>
            <Directory Id='ProgramFilesFolder'>
                <Directory Id='INSTALLDIR' Name='DirFilterApp'>
                    <Directory Id='DirFilterAppDrivers' Name='Drivers'>
                        <Directory Id='DirFilterDir' Name='DirFilter'>
                            <Component Id='DirFilterDriver' Guid='8c64e674-5476-46e4-93cd-ba1ae78622df'>
                                <File Id='DirFilterSYS' Name='DirFilter.sys' DiskId='1' Source='DirFilter.sys' KeyPath='yes' />
                                <File Id='DirFilterINF' Name='DirFilter.inf' DiskId='1' Source='DirFilter.inf' />
                                <File Id='DirFilterCAT' Name='' DiskId='1' Source='' />
                                <difx:Driver Legacy='yes' />
        <Feature Id='Complete' Level='1'>
            <ComponentRef Id='DirFilterDriver' />
        <UIRef Id="WixUI_Minimal" />

Several points are worth mentioning regarding this installer:

  • The XML schema for the WiX v3 DIFxApp extension is referenced at the top of the file. This is required for the Driver element to work. Note that in WiX v3, the Driver element is used instead of driver-specific attributes that were available for the Component element in the WiX v2 DIFxApp extension.
  • As said before, DIFx requires one driver per directory and one driver per .INF file. The driver component is placed in a directory under the application’s directory. Additional drivers will be placed in additional components under additional directories.
  • The “Legacy” attribute is used in the DIFx Driver element because my driver package is not WHQL signed. Of course the best solution for this is to ensure your driver is up to par and actually get WHQL certification. You should also note that Legacy mode disables integrity checks, allowing the driver installation to appear successful even when critical files are missing, etc.
  • Do NOT copy the GUIDs I used if you end copying and pasting from this example. Make sure you generate your own with uuidgen and replace them.

The .wxs source for this WiX installer is straightforward enough. However, actually compiling it and linking it requires referencing several external dependencies. When running Candle, the WiX compiler, the WixDifxAppExtension should be referenced (and others you may depend on, such as WixUIExtension). When running Light, the WiX linker, you should reference the extension as before. Additionally, in the newer builds of WiX v3.0, multiplatform support for DIFx requires you reference the .wixlib with the DIFxApp custom action DLLs for the appropriate platform:

E:\Projects\dirfilter\staging>%WIX_PATH%\candle -ext %WIX_PATH%\WixUIExtension.dll -ext %WIX_PATH%\WixDifxAppExtension.dll DirFilterInstaller.wxs
Microsoft (R) Windows Installer Xml Compiler version 3.0.4617.0
Copyright (C) Microsoft Corporation. All rights reserved.


E:\Projects\dirfilter\staging>%WIX_PATH%\light -ext %WIX_PATH%\WixUIExtension.dll -
ext %WIX_PATH%\WixDifxAppExtension.dll DirFilterInstaller.wixobj %WIX_PATH%\difx
-o DirFilterInstaller.msi
Microsoft (R) Windows Installer Xml Linker version 3.0.4617.0
Copyright (C) Microsoft Corporation. All rights reserved.

(The WIX_PATH environment variable is set to WiX 3.0’s bin directory on my system.)

Failing to reference WixDifxAppExtension or difxapp_[platform].wixlib will result in assorted compilation or linkage errors during installer build.

When debugging DIFxApp driver installation, usually the interesting things are performed by the SetupAPI directly and therefore the SetupAPI log should be examined first. However, DIFxApp’s custom actions write diagnostic information into the MSI log (which can be enabled with a command-line switch to msiexec) and can provide additional insight into the driver installation process. Here’s an excerpt from the MSI log of a successful DirFilter installation:

MSI (s) (2C:44) [20:22:39:061]: Executing op: ActionStart(Name=MsiInstallDrivers,,)
Action 20:22:39: MsiInstallDrivers.
MSI (s) (2C:44) [20:22:39:077]: Executing op: CustomActionSchedule(Action=MsiInstallDrivers,ActionType=3073,Source=BinaryData,Target=InstallDriverPackages,CustomActionData=2.15{8C64E674-5476-46E4-93CD-BA1AE78622DF}C:\Program Files\DirFilterApp\Drivers\DirFilter\82DirFilterInstallerKK)
MSI (s) (2C:90) [20:22:39:092]: Invoking remote custom action. DLL: C:\WINDOWS\Installer\MSI29.tmp, Entrypoint: InstallDriverPackages
DIFXAPP: ENTER: InstallDriverPackages()
DIFXAPP: INFO: 'CustomActionData' property 'DIFxApp Version' is '2.1'.
DIFXAPP: INFO: 'CustomActionData' property 'UI Level' is '5'.
DIFXAPP: INFO: 'CustomActionData' property 'componentId' is '{8C64E674-5476-46E4-93CD-BA1AE78622DF}'.
DIFXAPP: INFO: 'CustomActionData' property 'componentPath' is 'C:\Program Files\DirFilterApp\Drivers\DirFilter\'.
DIFXAPP: INFO: 'CustomActionData' property 'flags' is 0x8.
DIFXAPP: INFO: 'CustomActionData' property 'installState' is '2'.
DIFXAPP: INFO: 'CustomActionData' property 'ProductName' is 'DirFilterInstaller'.
DIFXAPP: INFO: 'CustomActionData' property 'ManufacturerName' is 'KK'.
DIFXAPP: INFO: user SID of user performing the install is 'S-1-5-21-1417001333-651377827-725345543-1003'.
DIFXAPP: INFO: opening HKEY_USERS\S-1-5-21-1417001333-651377827-725345543-1003\Software\Microsoft\Windows\CurrentVersion\DIFxApp\Components\{8C64E674-5476-46E4-93CD-BA1AE78622DF} (User's SID: 'S-1-5-21-1417001333-651377827-725345543-1003') ...
DIFXAPP: INFO: ENTER: DriverPackageInstallW
DIFXAPP: INFO: Copied 'DirFilter.inf' to driver store...
DIFXAPP: INFO: Copied '' to driver store...
DIFXAPP: INFO: Commiting queue...
DIFXAPP: INFO: Copied file: 'C:\Program Files\DirFilterApp\Drivers\DirFilter\dirfilter.sys' -> 'C:\WINDOWS\system32\DRVSTORE\DirFilter_11E71DD96C3AADF7CDEC882620E8410DECE9B5EF\dirfilter.sys'.
DIFXAPP: INFO: Installing INF file "C:\WINDOWS\system32\DRVSTORE\DirFilter_11E71DD96C3AADF7CDEC882620E8410DECE9B5EF\DirFilter.inf" of Type 4.
DIFXAPP: INFO: Installing File System Driver 'C:\WINDOWS\system32\DRVSTORE\DirFilter_11E71DD96C3AADF7CDEC882620E8410DECE9B5EF\DirFilter.inf'
DIFXAPP: INFO: Service 'DirFilter' was started
DIFXAPP: SUCCESS:Installation completed with code 0x0.
DIFXAPP: INFO: RETURN: DriverPackageInstallW (0x0)

DIFXAPP: INFO: ENTER: DriverPackageGetPathW
DIFXAPP: SUCCESS:Found driver store entry.
DIFXAPP: INFO: RETURN: DriverPackageGetPathW (0x7A)
DIFXAPP: INFO: ENTER: DriverPackageGetPathW
DIFXAPP: SUCCESS:Found driver store entry.
DIFXAPP: INFO: RETURN: DriverPackageGetPathW (0x0)
DIFXAPP: INFO: driver store entry for 'C:\Program Files\DirFilterApp\Drivers\DirFilter\DirFilter.inf' is 'C:\WINDOWS\system32\DRVSTORE\DirFilter_11E71DD96C3AADF7CDEC882620E8410DECE9B5EF\DirFilter.inf'.
DIFXAPP: INFO: The component Id '{8C64E674-5476-46E4-93CD-BA1AE78622DF}' is now set to point to driver store: 'C:\WINDOWS\system32\DRVSTORE\DirFilter_11E71DD96C3AADF7CDEC882620E8410DECE9B5EF\DirFilter.inf'
DIFXAPP: INFO: A reboot is not needed to install the component '{8C64E674-5476-46E4-93CD-BA1AE78622DF}'.
DIFXAPP: RETURN: InstallDriverPackages() 0 (0x0)

Notice how DIFxApp places a copy of your driver package in the system driver store, a behavior which is distinct from “right-click Install” .INF invocation. Notice also it reports whether the installation operation with SetupAPI was successful and will additionally take care of scheduling a reboot if the driver package so requires.

DIFxApp works equally well for installing a legacy file system filter. Simply use the FileSystemFilter DriverPackageType value instead.

Device class filters require special consideration. MSDN has a page about Installing a Filter Driver. For device filters, the process is straightforward – your .INF simply adds an UpperFilter under the appropriate device’s hardware key, using the special “HKR” relative root. However, a device class filter has no hardware key to refer to and indeed may wish to filter several distinct device classes. The MSDN page says one ought to write a custom “setup application” that shall invoke the .INF file for the several device classes of interest, as desired. However, DIFxApp offers no such flexibility and it does not appear that it can be used to drive such an .INF file. However, the fact it has a ClassFilter type clearly implies it has device class filters in mind.

As is often the case, the answer to this dillemma lies in the WDK. The WDK features a sample WiX v2.0 project for illustrating DIFxApp’s use, which in fact installs a class filter. In a default installation, you can find it in C:\WINDDK\6001.18000\src\setup\DIFxApp\WiXLib\ClassFilter.wxs. Nearby, in C:\WINDDK\6001.18000\src\setup\infs\clasfilt\ClasFilt.Inf, resides the sample .INF file. Among other things, the file includes an explicit registration as a class UpperFilter:

; Change {setup-ClassGUID} to the string form of the ClassGUID that you are installing the filter on.
; Change UpperFilters to LowerFilters if this is a lower class filter.
HKLM, System\CurrentControlSet\Control\Class\{setup-ClassGUID}, UpperFilters, 0x00010008, clasfilt

Fair enough. Multiple entries can be included in the registry section for UpperFilter registration directly under the class keys of interest. However, if you opt for this approach you may find to your dismay you no longer fall in ChkINF’s favor:

(W22.1.2213) INF files should not set registry entries under 'HKLM,System\CurrentControlSet\Control\Class'.

I guess you’re damned if you do and damned if you don’t. I suggest not drinking ChkINF’s Kool-Aid, setting up the device class filter registration directly and using DIFxApp rather than iterating with a custom setup application, obviously.

Hopefully this lengthy writeup will prove useful to other authors of MSI-based driver installations.

Implementing an LSA proxy authentication package

LSA authentication packages are a part of the core security ecosystem in Windows NT. LSA APs are provided with credentials by logon applications, such as Winlogon, authenticate these credentials and provide the logon application with a logon session handle if authentication was successful. Two authentication packages provided with Windows are of special interest. MSV1_0 authenticates user credentials against the local SAM database or against a domain controller through the legacy logon protocols. Kerberos.dll uses the Kerberos protocol with modern domain controllers (or third party KDCs, etc.) for establishing logon sessions.

Applications that want to provide value-added logon functionality wish to become involved in the logon process. Winlogon provides the GINA facility before Windows Vista and the new Credential Providers in Windows Vista and later to allow involvement in the end-user logon experience.

While customizing the logon process is done at the logon application side with GINAs or CPs, sometimes customization is required at the authentication side, in the Local Security Authority subsystem. For instance, a fingerprint reader may customize the logon UI to allow fingerprint scanning as a means of authentication. The customized logon application will call LsaLogonUser with the fingerprint scanner’s custom LSA authentication package as the desired authenticator. The fingerprint LSA AP will scan a fingerprint database it maintains to perform the authentication process. That would be an independent LSA authenticaion package.

There are other scenarios in which the regular MSV1_0/Kerberos based logon authentication process is desired, but special pre or post-processing is required. In Windows XP, the problematic GINA architecture makes replacing the GINA cumbersome, as multiple third-party applications may attempt to install conflicting GINA replacements. Indeed, Microsoft documentation has been modified retroactively to recommend GINA hooks and stubs in lieu of outright replacement of the MSGINA implementation previously suggested.

With the ability to instrument the logon application at the GINA side limited and version dependent (a totally different approach is required for Vista’s CPs), the alternative of instrumentation at the LSA side warrants exploration. We can implement an LSA proxy authentication package. Such a package would appear to the LSA server as an ordinary package, but would be implemented by delegating to original APs like MSV1_0 and Kerberos, providing it with monitoring and instrumentation capabilities.

LSA authentication packages are loaded by LSASS at system startup by enumerating them from the registry value HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Lsa\Security Packages. Both LSA authentication packages (APs) and security providers (SSPs) are registered at that location. For the purposes of this post, we’ll ignore pure SSPs and focus only on APs. We will register our proxy authentication package instead of MSV1_0 (and possibly Kerberos) at this location, and leave loading of the original APs to our proxy AP implementation.

Let us examine the system’s core APs, MSV1_0 and Kerberos:

C:\WINDOWS\system32>dumpbin /exports msv1_0.dll
Microsoft (R) COFF/PE Dumper Version 9.00.30729.01
Copyright (C) Microsoft Corporation. All rights reserved.
Dump of file msv1_0.dll
File Type: DLL
Section contains the following exports for msv1_0.dll
00000000 characteristics
48025C84 time date stamp Sun Apr 13 22:18:28 2008
0.00 version
1 ordinal base
32 number of functions
17 number of names
ordinal hint RVA name
5 0 0000175C LsaApCallPackage = _LsaApCallPackage@28
6 1 00014BC8 LsaApCallPackagePassthrough = _LsaApCallPackagePassthr
7 2 00014A59 LsaApCallPackageUntrusted = _LsaApCallPackageUntrusted
8 3 0000BDBB LsaApInitializePackage = _LsaApInitializePackage@20
9 4 0000F7FE LsaApLogonTerminated = _LsaApLogonTerminated@4
10 5 00007498 LsaApLogonUserEx2 = _LsaApLogonUserEx2@64
11 6 0001A7E5 Msv1_0ExportSubAuthenticationRoutine = _Msv1_0ExportSu
12 7 0001A7C6 Msv1_0SubAuthenticationPresent = _Msv1_0SubAuthenticat
13 8 00016E63 MsvGetLogonAttemptCount = _MsvGetLogonAttemptCount@0
2 9 0001B704 MsvIsLocalhostAliases = ?MsvIsLocalhostAliases@@YGHPAU
_UNICODE_STRING@@@Z (int __stdcall MsvIsLocalhostAliases(struct _UNICODE_STRING
14 A 00016E59 MsvSamLogoff = _MsvSamLogoff@12
15 B 0000A7BA MsvSamValidate = _MsvSamValidate@52
16 C 00016E6E MsvValidateTarget = _MsvValidateTarget@12
1 D 0000E415 SpInitialize = _SpInitialize@12
32 E 00006BC2 SpInstanceInit = _SpInstanceInit@12
3 F 0000F08F SpLsaModeInitialize = ?SpLsaModeInitialize@@YGJKPAKPAP
AU_SECPKG_FUNCTION_TABLE@@0@Z (long __stdcall SpLsaModeInitialize(unsigned long,
unsigned long *,struct _SECPKG_FUNCTION_TABLE * *,unsigned long *))
4 10 00006AE0 SpUserModeInitialize = ?SpUserModeInitialize@@YGJKPAKP
APAU_SECPKG_USER_FUNCTION_TABLE@@0@Z (long __stdcall SpUserModeInitialize(unsign
ed long,unsigned long *,struct _SECPKG_USER_FUNCTION_TABLE * *,unsigned long *))
2000 .data
2000 .reloc
2000 .rsrc
1D000 .text
C:\WINDOWS\system32>dumpbin /exports kerberos.dll
Microsoft (R) COFF/PE Dumper Version 9.00.30729.01
Copyright (C) Microsoft Corporation. All rights reserved.
Dump of file kerberos.dll
File Type: DLL
Section contains the following exports for Kerberos.dll
00000000 characteristics
48025C4A time date stamp Sun Apr 13 22:17:30 2008
0.00 version
1 ordinal base
32 number of functions
10 number of names
ordinal hint RVA name
5 0 00026F8A KerbCreateTokenFromTicket = _KerbCreateTokenFromTicket
2 1 00025773 KerbDomainChangeCallback = ?KerbDomainChangeCallback@@
6 2 000018B0 KerbFree = _KerbFree@4
7 3 00020A71 KerbIsInitialized = _KerbIsInitialized@0
8 4 00020A7C KerbKdcCallBack = _KerbKdcCallBack@0
9 5 0000380B KerbMakeKdcCall = _KerbMakeKdcCall@32
1 6 00013CAD SpInitialize = _SpInitialize@12
32 7 0000EDDF SpInstanceInit = _SpInstanceInit@12
3 8 000151DE SpLsaModeInitialize = ?SpLsaModeInitialize@@YGJKPAKPAP
AU_SECPKG_FUNCTION_TABLE@@0@Z (long __stdcall SpLsaModeInitialize(unsigned long,
unsigned long *,struct _SECPKG_FUNCTION_TABLE * *,unsigned long *))
4 9 0000ED1E SpUserModeInitialize = ?SpUserModeInitialize@@YGJKPAKP
APAU_SECPKG_USER_FUNCTION_TABLE@@0@Z (long __stdcall SpUserModeInitialize(unsign
ed long,unsigned long *,struct _SECPKG_USER_FUNCTION_TABLE * *,unsigned long *))
2000 .data
3000 .reloc
3000 .rsrc
43000 .text

Both DLLs export the SpInitialize function used for SSP initialization and for AP initialization export SpLsaModeInitialize and SpUserModeInitialize, called in LSASS context and in logon application context by secur32.dll, respectively.

As can be seen in MSV1_0’s export table, it provides a subauthentication package facility for those interested in becoming involved in the logon process. Clearly, this is the facility Microsoft intended third-parties to use, rather than creating proxy authentication packages. Unfortunately, subauthentication packages only provide a subset of authentication package functionality, primarily failing to provide access to the interactive logon (as opposed to the network logon) process. You should carefully consider your requirements. If they can be met with a subauthentication package, it is best to opt for that approach as it is far more likely to remain intact in Windows 7 and beyond. That said, the proxy authentication package model is given some legitimacy by this diagram, illustrating delegation to MSV1_0 by a hypothetical third-party custom authentication package.

It is interesting to note that MSV1_0 chooses to export the various LSA AP functions, such as LsaApLogonUserEx2, etc., via its DLL export table, while Kerberos opts not to export them, though quick examination of Kerberos.dll’s public symbols clearly illustrates the presence of the AP functions. So how does the LSA server know how to find and call the various AP functions? They are provided in a function dispatch table filled by the AP at initialization time, when SpLsaModeInitialize or SpUserModeInitialize are invoked (depending on the context of the AP’s use).

Keeping in mind that MSV1_0 was around before Kerberos was added to Windows NT in the Windows 2000 release and therefore may have remaining legacy cruft, reviewing the disassembly of the LSA server DLL, LSASRV, reveals that LSA first calls the Initialize functions to let the AP fill the function dispatch table, but then promptly examines the AP’s export table with GetProcAddress in the aptly named lsasrv!BindOldPackage function. This function appears to be invoked for the AP even when the function dispatch table has been filled. However, empirical evidence appears to suggest that the function dispatch table takes precedence over the contents of the export table. Indeed, Kerberos opts to do away with the export table entirely.

It appears that the export-based model was replaced with the dispatch table based model at some point during the lifetime of Windows NT. The export model has an obvious disadvantage of allowing a single DLL to implement only a single authentication package, a restriction will come back to later. The dispatch table model, on the other hand, allows the initialization function to return multiple dispatch tables, for multiple authentication packages, from a single DLL. This may yet prove useful for a proxy package.

In order to explore the feasibility of creating a proxy LSA authentication package, I wrote a test DLL, dubbed “LsaPrxAp”. This DLL provides the SpInitialize, SpLsaModeInitialize and SpUserModeInitialize exports. When invoked, it loads msv1_0 if it is not yet loaded. The DLL’s Initialize functions call the original msv1_0’s Initialize functions and then hook the authentication package by replacing function pointers with pointers to implementations of the LSA AP functions residing in LSAPrxAp. The original function pointers are saved in a global data structure so that LSAPrxAp’s stubs can invoke them while having value-added processing during the logon sequence. Since the name of the authentication package is the one provided in the SpLsaModeInitialize function by the AP, rather than the DLL’s name, it is easy to proxy the MSV1_0 module and become involved in the logon process. I did not bother with supporting Kerberos in my test, but hypothetically the proxy AP can call the Initialize functions for both MSV1_0 and Kerberos and return two dispatch tables as the parameter model for it allows.

Proxying a known authentication package of a known revision is one thing, but a more generic approach warrants special consideration. In both XP and Vista, the APs provide the latest LsaApLogonUserEx2 function. However, it is preceeded by LsaApLogonUserEx and LsaApLogonUser. The documentation for AP developers seems to indicate it is still legitimate to only support one of the older variants. Therefore, the proxy should take note that NULL function pointers in the dispatch table provided by the original APs are possible and should react accordingly.

As I investigated the behavior of the LSA server with respect to the export-based model for locating LSA AP functions vs. the function dispatch table model, I considered the problem of implementing a generic proxy if the dispatch table model was not preferred over the export table. The proxy AP would have to load the original AP and only have an LsaApLogonUserEx2 function if the original AP has. If the original AP has no LsaApLogonUser function exported, neither should the proxy AP. This presents special complication since compiling a different proxy AP for every possible set of exports is not feasible. I reiterate that the problem is theoretical since the function dispatch table model has no such fallacy.

In order to deal with this issue, I devised an approach where the proxy AP would initially export all possible LSA AP functions. At runtime, as the actual exports of the original AP is detected, functions that are missing from the original AP can be unexported from the proxy AP. I discuss the technique of unexporting functions through name obfuscation in the previous post.

Successfully compiling an LSA AP DLL required numerous acts of header juggling. For reference purposes, I provide the sequence I used:

#include <ntstatus.h>
#define WIN32_NO_STATUS
#include <Windows.h>
#include <NTSecAPI.h>
#define SECURITY_WIN32
#include <SSPI.h>

#ifndef NT_SUCCESS
#define NT_SUCCESS(Status) ((NTSTATUS)(Status) >= 0)

// LsaApCallPackageUntrusted is partially missing from NTSecPkg.h
typedef NTSTATUS
	__in PLSA_CLIENT_REQUEST ClientRequest,
	__in PVOID ProtocolSubmitBuffer,
	__in PVOID ClientBufferBase,
	__in ULONG SubmitBufferLength,
	__out PVOID* ProtocolReturnBuffer,
	__out PULONG ReturnBufferLength,
	__out PNTSTATUS ProtocolStatus

The WIN32_NO_STATUS definition is required to prevent Windows.h from defining the NTSTATUS values. Letting ntstatus.h define them is required because Windows.h only defines a subset of the required values. SSPI.h requires choosing between Win32, Kernel-mode and Macintosh Classic (heh…) usage, resulting in the SECURITY_WIN32 preprocessor definition. The NTSecPkg.h header included with the Windows SDK I’m using makes the embarrassing error of missing the prototype for LsaApCallPackageUntrusted, while curiously attempting to provide the function pointer type for it.

It is wise to avoid loading the original AP DLLs during DllMain, due to potential loader lock issues. The first functions invoked after an AP DLL has been mapped to a process are those that fill the function dispatch table; SpInitialize for the SSP case, SpLsaModeInitialize for the LSASS-side AP case and SpUserModeInitialize for the secur32.dll logon application (Winlogon) side case. All three functions ought to load the original AP if required and perform any required hooking of the dispatch tables, pointing to your own proxy functions.

The initialization functions should also extract the function pointers for the original AP implementations and preserve them in global data. This can later be used to forward calls to the original implementation. Consider the implementation of LsaApCallPackage in my LsaPrxAp test DLL:

	__in PLSA_CLIENT_REQUEST ClientRequest,
	__in PVOID ProtocolSubmitBuffer,
	__in PVOID ClientBufferBase,
	__in ULONG SubmitBufferLength,
	__out PVOID* ProtocolReturnBuffer,
	__out PULONG ReturnBufferLength,
	__out PNTSTATUS ProtocolStatus
	OutputDebugString(TEXT("lsaaprxap LsaApCallPackage\n"));

	return g_LsaPrxApFunctionTable.pLsaApCallPackage(
		ClientRequest, ProtocolSubmitBuffer, ClientBufferBase,
		SubmitBufferLength, ProtocolReturnBuffer, ReturnBufferLength,

Obviously a real-world proxy AP would perform required processing before or after forwarding to the original function pointer preserved in global data, as well.

Hopefully this primer on implementing an LSA proxy AP will prove to be a welcome addition to Microsoft’s sparse documentation on LSA authentication packages.