Vista Services.docx

Vista Services.docx

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VistaServices

ServicesinWindows Vista

November30,2009 

Abstract

ThispaperprovidesinformationaboutchangestoWindows®servicesthatwereintroducedinWindows Vista®.Italsoprovidessomebest-practicesguidelinesfordeveloperswhointendtoimplementservicesfortheseversionsofWindows.

Thisinformationappliestothefollowingoperatingsystems:

Windows 7

WindowsServer®2008R2

WindowsServer2008

WindowsVista

Referencesandresourcesdiscussedherearelistedattheendofthispaper.

ThecurrentversionofthispaperismaintainedontheWebat:

Disclaimer:

TheinformationcontainedinthisdocumentrepresentsthecurrentviewofMicrosoftCorporationontheissuesdiscussedasofthedateofpublication.BecauseMicrosoftmustrespondtochangingmarketconditions,itshouldnotbeinterpretedtobeacommitmentonthepartofMicrosoft,andMicrosoftcannotguaranteetheaccuracyofanyinformationpresentedafterthedateofpublication.

ThisWhitePaperisforinformationalpurposesonly.MICROSOFTMAKESNOWARRANTIES,EXPRESS,IMPLIEDORSTATUTORY,ASTOTHEINFORMATIONINTHISDOCUMENT.

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©2009MicrosoftCorporation.Allrightsreserved.

Microsoft,MSDN,VisualBasic,Windows,andWindowsVistaareeitherregisteredtrademarksortrademarksofMicrosoftCorporationintheUnitedStatesand/orothercountries.

Thenamesofactualcompaniesandproductsmentionedhereinmaybethetrademarksoftheirrespectiveowners.

DocumentHistory

Date

Change

November30,2009

UpdatedUIrequirementsandremovedunimplementedSCcommands.

August15,2006

Firstpublication

Contents

OverviewofWindowsServices3

HowServicesWork3

ChangestotheWindowsServicesModel4

SecurityEnhancements5

RunningwithLeastPrivilege5

ServiceIsolation7

RestrictedNetworkAccess10

Session 0Isolation11

PerformanceEnhancements12

DelayedAuto-Start12

ServiceStateChangeNotifications13

OtherEnhancements14

PreshutdownNotificationsandShutdownOrdering14

FailureDetectionandRecovery16

Resources18

OverviewofWindowsServices

Windows®servicesareapplicationsthattypicallystartwhenthecomputerisbootedandrunquietlyinthebackgrounduntilitisshutdown.Strictlyspeaking,aserviceisanyWindowsapplicationthatisimplementedwiththeservicesAPI.However,servicesnormallyhandlelow-leveltasksthatrequirelittleornouserinteraction.

Althoughservicesareofteneffectivelyinvisibletousers,Windowscannotfunctionnormallywithoutthem.Anumberofessentialoperatingsystemfunctionsarehandledbyservices,includingthefollowing:

∙Networking.Anumberofsystemservicessupportnetworking.Forexample,theDynamicHostConfigurationProtocol（DHCP）clientservicemanagesnetworkconfigurationbyregisteringandupdatingInternetProtocol（IP）addressesforthesystem.

∙Hardware.ThePlugandPlayserviceenablesacomputertorecognizeandrespondtochangesinitshardwareconfiguration,suchasauseraddingorremovinghardware.

∙Remoteaccess.TerminalServicesallowuserstologontoacomputerfromaremotelocation.

InadditiontoservicesthatarepartofWindows,mostcomputersalsohaveseveralthird-partyapplicationsthatrunpartlyorwhollyasservices.Commonexamplesofthird-partyservicesincludefirewallsandantivirusapplications.

ThiswhitepaperprovidesanoverviewofthechangestotheservicesmodelbeginningwithWindows Vista®.Italsoprovidessomebest-practicesguidelinesfordeveloperswhointendtoimplementservicesfortheseversionsofWindows.Fortheconvenienceofreaderswhomightnotbefamiliarwithservices,theremainderofthissectionprovidesabriefoverviewofhowservicesworkandhowtheyareimplemented.Formorecompleteinformation,seetheWindowsServicesdocumentationintheMSDN®Library.

HowServicesWork

TheprimarydifferencebetweenservicesandnormalapplicationsisthatservicesaremanagedbytheServiceControlManager（SCM）.ServicesareimplementedwiththeservicesAPI,whichhandlestheinteractionbetweentheSCMandservices.TheSCMmaintainsadatabaseofinstalledservicesandprovidesaunifiedwaytocontrolthem,including:

∙Startingandstoppingservices.

∙Managingrunningservices.

∙Maintainingservice-relatedstateinformation.

Servicesexistinoneofthreestates:

started,stopped,orpaused.

∙Startedisthenormalrunningstateforaservice.

∙Astoppedservicehasbeencompletelyshutdownandmustgothroughanormalstartupproceduretoenterthestartedstateagain.

∙Apausedservicesuspendsnormalprocessing,butremainsinmemoryandcontinuestorespondtocontrolrequests.Pausedservicescanthereforereturntothestartedstatewithoutgoingthroughthestartupprocedure.

Akeycharacteristicofaserviceishowitisstarted.TheSCMhasadatabasethatincludesinformationonhoweachserviceshouldbestarted.Thefollowingaretheservicestartuptypes:

∙Automatic.TheSCMautomaticallystartstheseservicesduringthesystem'sbootprocess.Theyareoftencalledauto-startservices.

∙Manual.TheseservicesmustbestartedmanuallywiththeControlPanelAdministrativeToolsapplication,withthesc.execommand-linetool,orprogrammaticallywiththeStartServicefunction.Theyareoftencalleddemand-startservices.Windows 7introducestrigger-startservices.Formoreinformation,see“DevelopingEfficientBackgroundProcessesforWindows”ontheWHDCWebsite.

∙Disabled.Theseservicescannotbestarted.Tostartadisabledservice,theusermustfirstchangethestartuptypetoautomaticormanual.

Afteraservicehasstarted,theSCMusescontrolrequeststomanagetheservice'sstate.Forexample,theSCMsendscontrolrequeststonotifyaservicethatitispausing,isresumingoperation,orshouldbepreparingtoshutdown.TheSCM'sdatabasealsocontainsthesecuritysettingsforeachservice.Thesesettingscontrolhowmuchaccessaservicehastosystemresourcesandenablesystemadministratorstocontrolaccesstoeachservice.

ChangestotheWindowsServicesModel

ServiceshavebeenanessentialpartofWindowsformanyyears.Theyenabledeveloperstocreatelong-runningexecutableapplicationsthat:

∙Canbeautomaticallystartedwhenthecomputerstarts.

∙Canbepausedandrestarted.

∙Canfunctionwhetherornotaninteractiveuserisloggedon.

∙Canruninthecontextofauseraccountthatisdifferentfromeitherthelogged-onuserorthedefaultcomputeraccount.

Thesefeaturesmakeservicesidealforscenarioswherethereisaneedforlong-runningfunctionalitythatdoesnotinterferewithuserswhoareworkingonthecomputer.However,sinceserviceswereintroduced,theenvironmentinwhichtheyfunctionhaschangedsubstantially.Thesechangeshavecreatedvariousissueswithsecurity,reliability,performance,management,andadministration.

ThissectiondiscussesenhancementsthatweremadetoWindows Vistatoaddressservice-relatedissues.

SecurityEnhancements

Inrecentyears,serviceshavebeenanattractivetargetforviruswriterswhowanttoattackWindows.RecentexamplesincludeBlaster,Sasser,andCodeRed.Thissituationoccursforanumberofreasons:

∙Servicesaretypicallylongrunning.Often,theystartwhenthesystembootsupandstopwhenitshutsdown.

∙Servicesareoftennetworkfacing,whichmakesthemespeciallyvulnerabletoremoteattacks.

∙Servicestypicallyruninahigh-privilegeaccountsuchasLocalSystem.

ThissectiondiscussestheenhancementsthatweremadetoWindows Vistatomitigatethesecurityissuesthatareassociatedwithservices.Thesechangesaddresstwoimportantgoals:

∙Limitingaccesstoservicesbyuserapplications.Session 0isolationrequiresservicesanduserapplicationstoruninseparatesessions.

∙”Hardening”servicestolimittheabilityofacompromisedservicetodamageasystem.Therearetwocomplementarywaystoaccomplishthisgoal:

Runningwithleastprivilegeallowsservicestorunwithonlythoseprivilegesthattheyneed,andnothingmore.

Serviceisolationallowsservicestoisolatethemselvesfromotherservicesorapplicationsbyusingauniqueserviceidentity.Aservicecanusethisidentitytorestrictaccesstoitsresourcesbyotherservicesorapplications.Aservicecanalsouseitsidentitytorestricttheservice'saccesstotheresourcesofotherservicesorapplications.Forexample,serviceisolationallowsanantivirusservicetomaintainexclusiveaccesstoitssignaturedefinitionfiles.

RunningwithLeastPrivilege

WindowsservicescommonlyrunintheLocalSystemaccount,themostp