Ukuhlaselwa okubili kwendlela yokubikezela isiteshi senqolobane kumaphrosesa e-AMD

Iqembu labacwaningi abavela e-Technical University of Graz (Austria), ngaphambilini elaziwa ngokusungula izindlela zokuhlasela MDS, I-NetSpecter, Umjikijelwa и ZombieLoad, yenze ucwaningo ekuthuthukisweni kwehadiwe okukhethekile kumaphrosesa we-AMD kanye ithuthukile izindlela ezimbili ezintsha zokuhlasela kwesiteshi eseceleni ezilawula ukuvuza kwedatha ngesikhathi sokusebenza kwendlela yokubikezela inqolobane yesiteshi se-L1 yamaphrosesa e-AMD. Amasu angasetshenziswa ukunciphisa ukusebenza kahle kokuvikelwa kwe-ASLR, ukubuyisela okhiye ekusetshenzisweni kwe-AES esengozini, nokwandisa ukusebenza kahle kokuhlasela kwe-Specter.

Izinkinga zitholwe ekusetshenzisweni kwendlela yokubikezela isiteshi (indlela yokubikezela) kunqolobane yedatha yezinga lokuqala le-CPU (L1D), esetshenziselwa ukubikezela ukuthi yisiphi isiteshi senqolobane esiqukethe ikheli elithile lememori. Ukulungiselelwa okusetshenziswe kuma-AMD processors kusekelwe ekuhloleni ama-μ-tag (μTag). μTag ibalwa ngokusebenzisa umsebenzi othize we-hashi ekhelini elibonakalayo. Ngesikhathi sokusebenza, injini yokubikezela isiteshi isebenzisa u-μTag ukuze inqume isiteshi senqolobane esivela etafuleni. Ngakho-ke, i-μTag ivumela iphrosesa ukuthi izikhawulele ekufinyeleleni isiteshi esithile kuphela, ngaphandle kokusesha kuzo zonke izinketho, okunciphisa kakhulu ukusetshenziswa kwamandla kwe-CPU.

Ngesikhathi sobunjiniyela obuhlehlayo bokusetshenziswa kohlelo lokubikezela isiteshi ezizukulwaneni ezahlukene zamaphrosesa e-AMD akhishwe kusukela ngo-2011 kuya ku-2019, kuhlonzwe izindlela ezimbili ezintsha zokuhlasela kwesiteshi:

• I-Collide+Probe - ivumela umhlaseli ukuthi alandelele ukufinyelela kwememori ngezinqubo ezisebenza kumongo ofanayo onengqondo we-CPU. Ingqikithi yendlela iwukusebenzisa amakheli abonakalayo abangela ukungqubuzana kumsebenzi we-hashi osetshenziselwa ukubala u-μTag ukulandelela ukufinyelela kwememori. Ngokungafani nokuhlasela kwe-Flush+Reload kanye ne-Prime+Probe esetshenziswa kuma-Intel processors, i-Collide+Probe ayisebenzisi inkumbulo eyabiwe futhi isebenza ngaphandle kolwazi lwamakheli wendawo.
• Layisha+Layisha kabusha - ikuvumela ukuthi unqume ngokunembe kakhulu ukulandelana kokufinyelela kwenkumbulo kumongo ofanayo we-CPU. Indlela isuselwe eqinisweni lokuthi iseli yenkumbulo yomzimba ingaba kunqolobane ye-L1D kanye. Labo. ukufinyelela iseli yememori efanayo ekhelini elihlukile le-virtual kuzobangela ukuthi iseli likhishwe kunqolobane ye-L1D, okuvumela ukufinyelela kwememori ukuthi kulandelelwe. Nakuba ukuhlasela kuncike kwinkumbulo eyabiwe, akushiyi imigqa yenqolobane, okuvumela ukuhlasela okuyimfihlo okungakhiphi idatha kunqolobane yezinga lokugcina.

Ngokusekelwe kumasu e-Collide+Probe kanye ne-Layisha+Layisha kabusha, abacwaningi babonise izimo ezimbalwa zokuhlasela kwesiteshi eseceleni:

• Amathuba okusebenzisa izindlela zokuhlela isiteshi sokuxhumana esingaqondile esifihliwe phakathi kwezinqubo ezimbili, okuvumela ukudluliswa kwedatha ngesivinini esifinyelela ku-588 kB ngomzuzwana, kuyaboniswa.
• Ngokusebenzisa ukungqubuzana ku-μTag, bekungenzeka ukunciphisa i-entropy yezinhlobonhlobo ezahlukene ze-ASLR (I-Address Space Layout Randomization) futhi kudlule ukuvikelwa kwe-ASLR ku-kernel ohlelweni lwe-Linux olubuyekezwe ngokuphelele. Amathuba okwenza ukuhlasela ukuze kuncishiswe i-ASLR entropy kokubili ezinhlelweni zabasebenzisi nokusebenzisa ikhodi ye-JavaScript eyenziwe endaweni ye-sandbox kanye nekhodi esebenza kwenye indawo yesivakashi iyaboniswa.
  

• Ngokusekelwe endleleni ye-Collide+Probe, ukuhlasela kwasetshenziswa ukuze kubuyiselwe ukhiye wokubethela ekusetshenzisweni okusengozini (ngokusekelwe I-T-table) Ukubethela kwe-AES.
• Ngokusebenzisa indlela ye-Collide+Probe njengesiteshi sokutholwa kwedatha, i-Specter attack ikwazile ukukhipha idatha yangasese ku-kernel ngaphandle kokusebenzisa inkumbulo eyabiwe.

Ukuba sengozini kwenzeka kuma-AMD processors asuselwe kuma-microarchitectures
Ugandaganda, Piledriver, Steamroller, Zen (Ryzen, Epic), Zen+ kanye Zen2.
I-AMD yaziswa ngalolu daba ngo-Agasti 23, 2019, kodwa kuze kube manje akazange awukhiphe umbiko ngolwazi mayelana nokuvimbela ukuba sengozini. Ngokwabacwaningi, inkinga ingavinjwa ezingeni lokubuyekeza i-microcode ngokunikeza izingcezu ze-MSR ukuze ukhethe ukukhubaza uhlelo lokubikezela isiteshi, okufana nalokho okwenziwa yi-Intel ukulawula ukukhutshazwa kwezindlela zokubikezela igatsha.

Source: opennet.ru