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SQL Server Programming and Host Protection Attributes

The ability to load and execute managed code in a SQL Server host requires meeting the host's requirements for both code access security and host resource protection. The code access security requirements are specified by one of three SQL Server permission sets: SAFE, EXTERNAL-ACCESS, or UNSAFE. Code executing within the SAFE or EXTERNAL-ACCESS permission sets must avoid certain types or members that have the HostProtectionAttribute attribute applied. The HostProtectionAttribute is not a security permission as much as a reliability guarantee in that it identifies specific code constructs, either types or methods, that the host may disallow. The use of the HostProtectionAttribute enforces a programming model that helps protect the stability of the host.

Host protection attributes identify types or members that do not fit the host programming model and represent the following increasing levels of reliability threat:

  • Are otherwise benign.

  • Could lead to destabilization of server-managed user code.

  • Could lead to destabilization of the server process itself.

SQL Server disallows the use of a type or member that has a HostProtectionAttribute that specifies a HostProtectionResource value of SharedState, Synchronization, MayLeakOnAbort, or ExternalProcessMgmt. This prevents the assemblies from calling members that enable sharing state, perform synchronization, might cause a resource leak on termination, or affect the integrity of the SQL Server process.

Disallowed Types and Members

The following table identifies types and members whose HostProtectionResource values are disallowed by SQL Server.

NamespaceType or member
Microsoft.Win32 PowerModeChangedEventArgs class

  PowerModeChangedEventHandler delegate

  SessionEndedEventArgs class

  SessionEndedEventHandler delegate

  SessionEndingEventArgs class

  SessionEndingEventHandler delegate

  SessionSwitchEventArgs class

  SessionSwitchEventHandler delegate

  SystemEvents class

  TimerElapsedEventArgs class

  TimerElapsedEventHandler delegate

  UserPreferenceChangedEventArgs class

  UserPreferenceChangingEventArgs class
System.Collections ArrayList.Synchronized method

  Hashtable.Synchronized method

  Queue.Synchronized method

  SortedList.Synchronized method

  Stack.Synchronized method
System.ComponentModel AddingNewEventArgs class

  AddingNewEventHandler delegate

  ArrayConverter class

  AsyncCompletedEventArgs class

  AsyncCompletedEventHandler delegate

  AsyncOperation class

  AsyncOperationManager class

  AttributeCollection class

  BackgroundWorker class

  BaseNumberConverter class

  BindingList<T> class

  BooleanConverter class

  ByteConverter class

  CancelEventArgs class

  CancelEventHandler delegate

  CharConverter class

  CollectionChangeEventArgs class

  CollectionChangeEventHandler delegate

  CollectionConverter class

  ComponentCollection class

  ComponentConverter class

  ComponentEditor class

  ComponentResourceManager class

  Container class

  ContainerFilterService class

  CultureInfoConverter class

  CustomTypeDescriptor class

  DateTimeConverter class

  DecimalConverter class

  ActiveDesignerEventArgs class

  ActiveDesignerEventHandler delegate

  CheckoutException class

  CommandID class

  ComponentChangedEventArgs class

  ComponentChangedEventHandler delegate

  ComponentChangingEventArgs class

  ComponentChangingEventHandler delegate

  ComponentEventArgs class

  ComponentEventHandler delegate

  ComponentRenameEventArgs class

  ComponentRenameEventHandler delegate

  DesignerCollection class

  DesignerEventArgs class

  DesignerEventHandler delegate

  DesignerOptionService class

  DesignerTransaction class

  DesignerTransactionCloseEventArgs class

  DesignerTransactionCloseEventHandler delegate

  DesignerVerb class

  DesignerVerbCollection class

  DesigntimeLicenseContext class

  DesigntimeLicenseContextSerializer class

  MenuCommand class

  ComponentSerializationService class

  ContextStack class

  DesignerLoader class

  InstanceDescriptor class

  MemberRelationshipService class

  ResolveNameEventArgs class

  ResolveNameEventHandler delegate

  SerializationStore class

  ServiceContainer class

  ServiceCreatorCallback delegate

  StandardCommands class

  StandardToolWindows class

  DoubleConverter class

  DoWorkEventArgs class

  DoWorkEventHandler delegate

  EnumConverter class

  EventDescriptor class

  EventDescriptorCollection class

  EventHandlerList class

  ExpandableObjectConverter class

  HandledEventArgs class

  HandledEventHandler delegate

  InstanceCreationEditor class

  Int16Converter class

  Int32Converter class

  Int64Converter class

  InvalidAsynchronousStateException class

  InvalidEnumArgumentException class

  BeginInvoke method

  License class

  LicenseContext class

  LicenseException class

  LicenseManager class

  LicenseProvider class

  LicFileLicenseProvider class

  ListChangedEventArgs class

  ListChangedEventHandler delegate

  ListSortDescription class

  ListSortDescriptionCollection class

  MaskedTextProvider class

  MemberDescriptor class

  MultilineStringConverter class

  NestedContainer class

  NullableConverter class

  ProgressChangedEventArgs class

  ProgressChangedEventHandler delegate

  PropertyChangedEventArgs class

  PropertyChangedEventHandler delegate

  PropertyDescriptor class

  PropertyDescriptorCollection class

  ReferenceConverter class

  RefreshEventArgs class

  RefreshEventHandler delegate

  RunWorkerCompletedEventArgs class

  RunWorkerCompletedEventHandler delegate

  SByteConverter class

  SingleConverter class

  StringConverter class

  SyntaxCheck class

  TimeSpanConverter class

  TypeConverter class

  TypeDescriptionProvider class

  TypeDescriptor class

  TypeListConverter class

  UInt16Converter class

  UInt32Converter class

  UInt64Converter class

  WarningException class

  Win32Exception class
System.Diagnostics Debug.Listeners property

  Trace.Listeners property

  EventLog.SynchronizingObject property

  ConsoleTraceListener class

  DefaultTraceListener class

  DelimitedListTraceListener class

  EventLogTraceListener class

  PerformanceCounter class

  PerformanceCounterCategory class

  Process class

  ProcessStartInfo class

  TextWriterTraceListener class

  TraceListener class

  XmlWriterTraceListener class

  TraceSource.Listeners property
System.IO Stream.Synchronized method

  TextReader.Synchronized method

  TextWriter.Synchronized method
System.Reflection.Emit ConstructorBuilder class

  EventBuilder class

  FieldBuilder class

  MethodBuilder class

  CustomAttributeBuilder class

  MethodRental class

  ModuleBuilder class

  PropertyBuilder class

  TypeBuilder class

  UnmanagedMarshal class
System.Text Group.Synchronized method

  Match.Synchronized method
System.Threading AutoResetEvent class

  EventWaitHandle class

  ManualResetEvent class

  Monitor class

  Mutex class

  ReaderWriterLock class

  Semaphore class

  Thread.AllocateNamedDataSlot method

  Thread.BeginCriticalRegion method

  Thread.EndCriticalRegion method

  Thread.FreeNamedDataSlot method

  Thread.GetData method

  Thread.Join method

  Thread.SetApartmentState method

  Thread.SetData method

  Thread.SpinWait method

  Thread.Start method

  Thread.TrySetApartmentState method

  ThreadPool class

  Timer class
System.Timers Timer class
System.Web.Configuration MachineKeyValidationConverter class
System.Windows.Forms AutoCompleteStringCollection.SyncRoot property

SQL Server allows users to specify the reliability requirements for code deployed into a database. When assemblies are uploaded into the database, the author of the assembly can specify one of three permission sets for that assembly: SAFE, EXTERNAL-ACCESS, or UNSAFE.

Code access securityExecute onlyExecute + access to external resourcesUnrestricted
Programming model restrictionsYesYesNo restrictions
Verifiability requirementYesYesNo
Ability to call native codeNoNoYes

SAFE is the most reliable and secure mode with associated restrictions in terms of the allowed programming model. SAFE code has high reliability and security features. SAFE assemblies are given enough permission to run, perform computations, and have access to the local database. SAFE assemblies need to be verifiably type safe and are not allowed to call unmanaged code.

EXTERNAL-ACCESS provides an intermediate security option, allowing code to access resources external to the database but still having the reliability and safety of SAFE.

UNSAFE is for highly trusted code that can only be created by database administrators. This trusted code has no code access restrictions, and it can call unmanaged (native) code.

SQL Server uses the host-level code access security policy layer to set up a host policy that grants one of the three sets of permissions based on the permission set stored in SQL Server catalogs. Managed code running inside the database always gets one of these code access permission sets.

The programming model for managed code in SQL Server requires functions, procedures, and types which do not require the use of state held across multiple invocations or the sharing of state across multiple user sessions. Further, as described earlier, the presence of shared state can cause critical exceptions that impact the scalability and the reliability of the application.

Given these considerations, SQL Server disallows the use of static variables and static data members. For SAFE and EXTERNAL-ACCESS assemblies, SQL Server examines the metadata of the assembly at CREATE ASSEMBLY time, and fails the creation of such assemblies if it finds the use of static data members and variables.