c++macos-catalina iokit macos-system-extension driverkit

kIOReturnNotPermitted from IOServiceOpen connecting to SystemExtension IOService

I am trying to create a client connection to a SystemExtension IOService. I can see that my IOUserClient subclass is created (init() and Start(IOService*) is called), but the return code from IOServiceOpen returns kIOReturnNotPermitted.

I am making the call to IOServiceOpen from the same app that creates the activation request.

Entitlements for app that makes the activation request / call to IOServiceOpen:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>com.apple.developer.driverkit.userclient-access</key>
  <array>
    <string>sc.example.MyUserUSBInterfaceDriver</string>
  </array>
    <key>com.apple.developer.system-extension.install</key>
    <true/>
    <key>com.apple.developer.system-extension.uninstall</key>
    <true/>
</dict>
</plist>

Entitlements for the dext:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>com.apple.developer.driverkit.userclient-access</key>
  <array>
    <string>sc.example.USBApp</string>
  </array>
    <key>com.apple.developer.driverkit</key>
    <true/>
    <key>com.apple.developer.driverkit.transport.usb</key>
    <true/>
</dict>
</plist>

MyUserClient:

#ifndef MyUserClient_h
#define MyUserClient_h

#include <DriverKit/IOUserClient.iig>

class MyUserClient : public IOUserClient {
public:
  bool init() override;
  kern_return_t Start(IOService* provider) override;
  kern_return_t Stop(IOService* provider) override;
  void free() override;
};

#endif /* MyUserClient_h */

bool MyUserClient::init() {
  LOG();
  if (!super::init()) {
    LOG("super::init() failed");
    return false;
  }
  return true;
}

kern_return_t IMPL(MyUserClient, Start) {
  LOG();
  auto ret = Start(provider, SUPERDISPATCH);
  if (ret != kIOReturnSuccess) {
    LOG("SUPERDISPATCH Start failed, ret: %{public}d", ret);
  }
  return ret;
}

kern_return_t IMPL(MyUserClient, Stop) {
  LOG();
  auto ret = Stop(provider, SUPERDISPATCH);
  if (ret != kIOReturnSuccess) {
    LOG("SUPERDISPATCH Stop failed, ret: %{public}d", ret);
  }
  return ret;
}

void MyUserClient::free() {
  super::free();
  LOG();
}

LOG is just a macro that does os_log(OS_LOG_DEFAULT, ...

NewUserClient implementation:

kern_return_t IMPL(MyUserUSBInterfaceDriver, NewUserClient) {
  LOG("%{public}d:", type);

  IOService* client;

  auto ret = Create(this, "UserClientProperties", &client);
  *userClient = OSDynamicCast(IOUserClient, client);
  if (!(*userClient) || ret != kIOReturnSuccess) {
    LOG("Failed to create IOUserClient, %{public}d", ret);
  }
  return ret;
}

Code to connect to system extension:

void connectToDext(io_service_t* serviceObject) {
  io_connect_t dataPort;

  kern_return_t kernResult =IOServiceOpen(*serviceObject, mach_task_self(), 123, &dataPort);
  if (kernResult != KERN_SUCCESS) {
    printf("IOServicceOpen failed: %d, %s\n", kernResult, kern_return_t_toCStr(kernResult));
  }
  kernResult = IOServiceClose(dataPort);
  if (kernResult != KERN_SUCCESS) {
    printf("IOServicceClosed failed: %d, %s\n", kernResult, kern_return_t_toCStr(kernResult));
  }
}

int connectToFirstDext() {
      CFMutableDictionaryRef matchingDict;
      matchingDict = IOServiceMatching("IOService");

      if (matchingDict == 0) {
        return -1;
      }

      io_iterator_t iter;
      if (IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict, &iter) !=
          KERN_SUCCESS) {
        printf("IOServiceGetMatchingServices failed.\n");
        return -1;
      }

      io_service_t device;
      while ((device = IOIteratorNext(iter))) {
        io_name_t deviceName;
        if (IORegistryEntryGetName(device, deviceName) == KERN_SUCCESS) {
          printf("name: %s\n", deviceName);
          if (strcmp(deviceName, "MyUserUSBInterfaceDriver") == 0) {
            printf("Calling connect\n");
            connectToDext(&device);
          }
        }
        IOObjectRelease(device);
      }

      IOObjectRelease(iter);

    return 0;
}

Edit:

Info.plist of app

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>BuildMachineOSBuild</key>
    <string>19E287</string>
    <key>CFBundleDevelopmentRegion</key>
    <string>en</string>
    <key>CFBundleExecutable</key>
    <string>USBApp</string>
    <key>CFBundleIdentifier</key>
    <string>sc.example.USBApp</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>USBApp</string>
    <key>CFBundlePackageType</key>
    <string>APPL</string>
    <key>CFBundleShortVersionString</key>
    <string>1.0</string>
    <key>CFBundleSupportedPlatforms</key>
    <array>
        <string>MacOSX</string>
    </array>
    <key>CFBundleVersion</key>
    <string>1</string>
    <key>DTCompiler</key>
    <string>com.apple.compilers.llvm.clang.1_0</string>
    <key>DTPlatformBuild</key>
    <string>11E503a</string>
    <key>DTPlatformVersion</key>
    <string>GM</string>
    <key>DTSDKBuild</key>
    <string>19E258</string>
    <key>DTSDKName</key>
    <string>macosx10.15</string>
    <key>DTXcode</key>
    <string>1141</string>
    <key>DTXcodeBuild</key>
    <string>11E503a</string>
    <key>LSMinimumSystemVersion</key>
    <string>10.15</string>
    <key>NSHumanReadableCopyright</key>
    <string>Copyright © 2020 Example. All rights reserved.</string>
    <key>NSMainNibFile</key>
    <string>MainMenu</string>
    <key>NSPrincipalClass</key>
    <string>NSApplication</string>
    <key>NSSupportsAutomaticTermination</key>
    <true/>
    <key>NSSupportsSuddenTermination</key>
    <true/>
</dict>
</plist>

Info.plist of dext:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>BuildMachineOSBuild</key>
    <string>19E287</string>
    <key>CFBundleDevelopmentRegion</key>
    <string>en</string>
    <key>CFBundleExecutable</key>
    <string>sc.example.MyUserUSBInterfaceDriver</string>
    <key>CFBundleIdentifier</key>
    <string>sc.example.MyUserUSBInterfaceDriver</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>sc.example.MyUserUSBInterfaceDriver</string>
    <key>CFBundlePackageType</key>
    <string>DEXT</string>
    <key>CFBundleShortVersionString</key>
    <string>1.0</string>
    <key>CFBundleSupportedPlatforms</key>
    <array>
        <string>MacOSX</string>
    </array>
    <key>CFBundleVersion</key>
    <string>1</string>
    <key>DTCompiler</key>
    <string>com.apple.compilers.llvm.clang.1_0</string>
    <key>DTPlatformBuild</key>
    <string>11E503a</string>
    <key>DTPlatformVersion</key>
    <string>GM</string>
    <key>DTSDKBuild</key>
    <string></string>
    <key>DTSDKName</key>
    <string>driverkit.macosx19.0</string>
    <key>DTXcode</key>
    <string>1141</string>
    <key>DTXcodeBuild</key>
    <string>11E503a</string>
    <key>IOKitPersonalities</key>
    <dict>
        <key>example_device</key>
        <dict>
            <key>CFBundleIdentifier</key>
            <string>sc.example.MyUserUSBInterfaceDriver</string>
            <key>IOClass</key>
            <string>IOUserService</string>
            <key>IOProviderClass</key>
            <string>IOUSBHostInterface</string>
            <key>IOUserClass</key>
            <string>MyUserUSBInterfaceDriver</string>
            <key>IOUserServerName</key>
            <string>sc.example.MyUserUSBInterfaceDriver</string>
            <key>UserClientProperties</key>
            <dict>
                <key>IOClass</key>
                <string>IOUserUserClient</string>
                <key>IOServiceDEXTEntitlements</key>
                <string></string>
                <key>IOUserClass</key>
                <string>MyUserClient</string>
            </dict>
            <key>bConfigurationValue</key>
            <integer>1</integer>
            <key>bInterfaceNumber</key>
            <integer>0</integer>
            <key>idProduct</key>
            <integer>8</integer>
            <key>idVendor</key>
            <integer>1234</integer>
        </dict>     
    </dict>
    <key>OSBundleUsageDescription</key>
    <string>Example user space USB driver</string>
    <key>OSMinimumDriverKitVersion</key>
    <string>19.4</string>
</dict>
</plist>

Solution

Updated answer:

The IOServiceDEXTEntitlements property in your IOKitPersonality's Info.plist's user client property dictionary should be one of:

Missing entirely; this means: don't check client entitlements beyond basics listed below in my original answer.
I think, an array of arrays of strings; the client must have all the entitlements listed in one of the inner arrays. (NB: I haven't done any testing with this latter case.)

A non-array or empty-array IOServiceDEXTEntitlements property means the client can't match the entitlements in one of the inner arrays, as there aren't any. The check therefore always fails with kIOReturnNotPermitted. This is what's happening with your (empty) string value.

For details, check the code in IOUserServer::checkEntitlements() and where it's called from in IOUserServer::serviceNewUserClient() in IOUserServer.cpp from the xnu source code.

Original answer:

(Given prior to the contents of the Info.plists being posted.)

I don't see anything obviously wrong with what you've posted, so I suspect your problem might be caused by something you haven't posted. Things to watch out for:

The user client app's com.apple.developer.driverkit.userclient-access array must contain the dext's bundle ID. Perhaps double-check that this ID really is equal to sc.example.MyUserUSBInterfaceDriver? (I've previously spent over an hour tearing my hair out over the kIOReturnNotPermitted error when I had a typo here.)
The user client app must be permitted to talk to IOKit. This is the case by default, unless your app is sandboxed. Assuming the entitlements you've posted are complete, your app isn't sandboxed, so that shouldn't be the problem.
If the dictionary used for creating the new user client contains the IOServiceDEXTEntitlements key, the user space app must have all entitlements listed there. (This dictionary comes from the dext's info.plist, which you haven't posted yet at time of writing.)
I believe the dext and the app must be signed using the same team ID. (I seem to remember there is an entitlement you can set on the dext to work around this requirement however.) Perhaps double-check the TeamIdentifier using codesign -dv path/to/your.dext and codesign -dv path/to/your.app