Ukuba zixhatshaziwe, ezi ziphene zinokuvumela abahlaseli ukuba bafumane ukufikelela okungagunyaziswanga kulwazi olubuthathaka okanye ngokubanzi babangele iingxaki.
Iqela le Abaphandi abavela kwiiyunivesithi zaseTshayina nase-United States bachonge ubuthathaka obutsha kwiiprosesa Intel ekhokelela ekuvuzeni kolwazi kwisiphumo semisebenzi eqikelelwayo ngokusebenzisa iziteshi zomntu wesithathu, ezinokusetyenziswa, umzekelo, ukuququzelela umjelo wonxibelelwano ofihlakeleyo phakathi kweenkqubo okanye ukufumanisa ukuvuza ngexesha lokuhlaselwa kwe-Meltdown.
Undoqo wokuba sesichengeni lutshintsho kwirejista yeprosesa ye-EFLAGS, okwenzekayo ngenxa yokwenziwa kwemiyalelo eqikelelwayo, kuchaphazela ixesha elilandelayo lokwenziwa kwemiyalelo ye-JCC (gxuma xa iimeko ezichaziweyo zidibene).
Imisebenzi eqikelelwayo ayigqitywanga kwaye isiphumo siyalahlwa, kodwa utshintsho olulahliweyo lwe-EFLAGS lunokumiselwa ngokuhlalutya ixesha lokwenziwa kwemiyalelo ye-JCC. Imisebenzi eqikelelweyo yokuthelekisa yangaphambi kokutsiba, ukuba uthelekiso luphumelele, lubangela ukulibaziseka okuncinci okunokulinganiswa kwaye kusetyenziswe njengento ehambelana nomxholo.
Uhlaselo lokubulawa okwexeshana luhlobo lohlaselo olusebenzisa ukuba sesichengeni kwetekhnoloji yokuphucula i-CPU. Uhlaselo olutsha luvela ngokukhawuleza. Ijelo elisecaleni liyinxalenye ephambili yokuhlaselwa kwexesha elifutshane lokukhupha idatha.
Kulo msebenzi, sifumene ubuthathaka obutshintshe irejista ye-EFLAGS ekusebenzeni okwethutyana enokuthi ibe nefuthe elibi kwi-Jcc (Jump Condition Code) umyalelo kwi-Intel CPUs. Ngokusekwe ekufumaneni kwethu, sicebisa uhlaselo lwetshaneli esecaleni elisebenzisa ixesha elifutshane lokwenziwa kunye nemiyalelo ye-Jcc ukuhambisa idatha.
Olu hlaselo lufihla idatha eyimfihlo ngokutshintsha irejistri ebangela ukuba ixesha lokubulawa licothe kancinci kwaye elinokulinganiswa ngumhlaseli ukucacisa idatha. Olu hlaselo aluxhomekeke kwinkqubo ye-cache.
Ngokungafaniyo nolunye uhlaselo efanayo ngokusebenzisa itshaneli yomntu wesithathu, indlela entsha ayihlalutyi utshintsho kwixesha lokufikelela kwidatha egciniweyo kwaye ayigcinwanga kwaye ayifuni inyathelo lokusetha kwakhona irekhodi ye-EFLAGS kwisimo sokuqala, okwenza kube nzima ukufumanisa nokuvimbela ukuhlaselwa.
yedemo, abaphandi baphumeze ukwahluka kohlaselo lweMeltdown, usebenzisa kuyo indlela entsha yokufumana ulwazi malunga nesiphumo somsebenzi oqikelelwayo. Ukusebenza kwendlela yokulungelelanisa ukuvuza kolwazi ngexesha lohlaselo lwe-Meltdown iboniswe ngempumelelo kwiinkqubo kunye ne-Intel Core i7-6700 kunye ne-i7-7700 CPUs kwindawo enoBuntu 22.04 kernel kunye neLinux 5.15. Kwinkqubo ene-Intel i9-10980XE CPU, uhlaselo lube yimpumelelo nje kancinane.
Ukuba sesichengeni kweMeltdown kusekelwe kwinto yokuba ngexesha lokwenziwa kwemiyalelo eqikelelwayo, umqhubekekisi unokufikelela kwindawo yedatha yabucala kwaye emva koko ulahle isiphumo, kuba amalungelo amiselweyo athintela ukufikelela okunjalo kwinkqubo yomsebenzisi.
Kwinkqubo, ibhloko eyenziwe ngokuqikelelwayo ihlukaniswe kwikhowudi ephambili ngokutsiba okunemiqathango, ekuthi kwiimeko zokwenyani isoloko ishukunyiswa, kodwa ngenxa yokuba inkcazo enemiqathango isebenzisa ixabiso elibaliweyo elingaziwa kwiprosesa ngexesha lekhowudi yokulungiselela. . ufezekiso, zonke iinketho zesebe ziyenziwa ngokuqikelelwa.
Kwi-Meltdown yakudala, ukusukela ukuba indawo efihlakeleyo enye isetyenziselwa imisebenzi eqikelelweyo njengemiyalelo eyenziwa ngokuqhelekileyo, kuyenzeka ngexesha lentelekelelo yophumezo ukuseta iziphawuli kwindawo efihlakeleyo ebonisa imixholo yamasuntswana alodwa kwindawo yenkumbulo evaliweyo, kwaye emva koko ngokwesiqhelo yenziwe. ikhowudi ukumisela intsingiselo yayo ngokuhlalutya ixesha lofikelelo kwi-cached kunye nedatha engagcinwanga.
Ukwahluka okutsha kusebenzisa utshintsho kwirejista ye-EFLAGS njengophawu lokuvuza. Kwi-demo ye-Covert Channel, enye inkqubo imodareyitha idatha ethunyelwayo ukuze itshintshe imixholo yerekhodi ye-EFLAGS, kwaye enye inkqubo yahlula utshintsho kwi-JCC yexesha lokusebenza ukuze iphinde idale idatha ethunyelwe yinkqubo yokuqala.
Okokugqibela, ukuba unomdla wokwazi okungakumbi ngayo, unokujonga kwi iinkcukacha kwikhonkco elilandelayo.