Chapter14isasubsetofWhatprotectionproblemsmayariseifasharedstackisusedforparameterpassingThecontentsofthestackcouldbecompromisedbyotherprocessessharingthestackConsideracomputingenvironmentwhereau ID: 457647
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PracticeExercisesWhatarethemaindifferencesbetweencapabilitylistsandaccesslists?Anaccesslistisalistforeachobjectconsistingofthedomainswithanonemptysetofaccessrightsforthatobject.Acapabilitylistisalistofobjectsandtheoperationsallowedonthoseobjectsforeachdomain.ABurroughsB7000/B6000Þlecanbetaggedassensitivedata.WhensuchaÞleisdeleted,itsstorageareaisoverwrittenbysomerandombits.Forwhatpurposewouldsuchaschemebeuseful? Chapter14)isasubsetofWhatprotectionproblemsmayariseifasharedstackisusedforparameterpassing?Thecontentsofthestackcouldbecompromisedbyotherprocess(es)sharingthestack.Consideracomputingenvironmentwhereauniquenumberisassoci-atedwitheachprocessandeachobjectinthesystem.Supposethatweallowaprocesswithnumbertoaccessanobjectwithnumber.Whattypeofprotectionstructuredowehave?Hierarchicalstructure.Consideracomputingenvironmentwhereaprocessisgiventheprivilegeofaccessinganobjectonlytimes.Suggestaschemeforimplementingthispolicy.Addanintegercounterwiththecapability.Ifalltheaccessrightstoanobjectaredeleted,theobjectcannolongerbeaccessed.Atthispoint,theobjectshouldalsobedeleted,andthespaceitoccupiesshouldbereturnedtothesystem.SuggestanefÞcientimplementationofthisscheme.Referencecounts.WhyisitdifÞculttoprotectasysteminwhichusersareallowedtodotheirownI/OInearlierchaptersweidentiÞedadistinctionbetweenkernelandusermodewherekernelmodeisusedforcarryingoutprivilegedoperationssuchasI/O.OnereasonwhyI/OmustbeperformedinkernelmodeisthatI/Orequiresaccessingthehardwareandproperaccesstothehardwareisnecessaryforsystemintegrity.IfweallowuserstoperformtheirownI/O,wecannotguaranteesystemintegrity.Capabilitylistsareusuallykeptwithintheaddressspaceoftheuser.Howdoesthesystemensurethattheusercannotmodifythecontentsofthelist?Acapabilitylistisconsideredaprotectedobjectandisaccessedonlyindirectlybytheuser.Theoperatingsystemensurestheusercannotaccessthecapabilitylistdirectly.