Mazuva mashoma apfuura boka revatsvakurudzi vanobva kuUniversity University yeDresden rakafumurwa zvavakaona kutambura (CVE-2020-12965) iyo inogonesa Meltdown-kirasi kurwisa paZen + uye Zen 2-based AMD processor.
Pakutanga, AMD Zen + uye Zen 2 processor yaifungidzirwa kuti haigoni kubatwa kusvika pakunyungudika kweMeltdown, asi vaongorori vakaona hunhu iyo inotungamira kune yekufungidzira kuwana kune yakachengetedzwa nzvimbo dzekurangarira kana uchishandisa asiri eecanonical chaiwo kero.
Vanoongororas taura kuti iyo AMD64 dhizaini inosanganisira kushandisa chete ekutanga makumi mabhii makumi mana yekero chaiyo uye usafarire iwo akasara gumi nematanhatu bits uye neizvi zvataurwa kuti bits 48 kusvika 63 inofanira kugara ichiteedzera kukosha kwe bit 47.
Ndinoreva kana chiitiko ichi chikatyorwa uye kuyedza kunoitwa kugadzirisa kero ine hunhu hwekupokana hwepamusoro mabheti, processor inokanda musiyano. Iyo inodzokororwa padding yemusoro mabheti inotungamira kune kupatsanurwa kweinowanikwa kero nzvimbo munzvimbo mbiri mabhuroko.
Kero dzinokwana mukati memabhureki akasarudzika dzinodaidzwa kuti canonical, uye adhiresi dzisiri dzacho dzine humboo hwepamusoro dzinodaidzwa kuti dzisiri-canonical. Iyo yepazasi renji yekanoni kero, sekutonga, inogoverwa yeiyo data data, uye iyo yepamusoro renji inoshandiswa kune kernel data (kuwana kune yakatarwa kero kubva kune mushandisi nzvimbo yakavharirwa padanho rekuparadzaniswa kwemikana).
Iyo yakasarudzika kunetseka Kunyungudika kunoenderana nenyaya yekuti panguva yekufungidzira kuuraya Mirayiridzo, processor inogona kuwana yakavanzika dhata nzvimbo uye wozorasa mhedzisiro, sezvo ropafadzo dzakagadzwa dzinorambidza kuwana kwakadai kubva pamushandisi maitiro.
Muchirongwa, blockcha yekufungidzira yakaitwa yakaparadzaniswa nekodhi huru nebazi rine mamiriro, iro mumamiriro chaiwo rinogara richipisa, asi nekuda kwekuti chirevo chine chirevo chinoshandisa kukosha kwakatarwa uko processor isingazive panguva yekufungidzira kuuraya kodhi, yekufungidzira kuitiswa kwesarudzo dzese dzemubazi dzinoitika.
Sezvo lfungidziro mashandisiro anoshandisa imwechete cache pane zvinowanzoitwa mirairo, zvinogoneka panguva yekuurayiwa yekufungidzira caching mabhukumaki ayo ratidza zvirimo zvemunhu mabiti munzvimbo yakavharika ndangariro, uyezve mune yakajairwa kodhi kuona kukosha kwayo kuburikidza neNguva yekuongorora inowana yakachengetwa uye isina-cached dhata.
Iko kusarudzika kwekushushikana kutsva inokanganisa AMD Zen + uye Zen 2 processor, ndeyekuti maCPU anotendera kwekufungidzira kuuraya verenga uye nyora mashandiro ayo anowana ndangariro uchishandisa zvisiri pamutemo kero dzisiri, kungozeya mabhuru epamusoro gumi nematanhatu.
Naizvozvo, mune yekufungidzira kodhi kuitisa maitiro, processor yacho inongoshandisa chete ezasi makumi mabhii makumi mana nemasere nekero kusimbiswa kunoitwa zvakasiyana. Kana, kana uchidudzira isiri-canonical chaiyo kero kune chaiyo kero mune inosanganisirwa dudziro buffer (TLB) kana chikamu chekereke chekero ichienderana, yekufungidzira mutoro mashandiro anodzosera kukosha kunyangwe zvirimo zvemukati epamusoro gumi nematanhatu, zvichitendera iwe kupfuudza ndangariro kugovana pakati peshinda. Gare gare, mashandiro acho anozoshomeka uye akaraswa, asi kuwana ndangariro kuchaitwa uye iyo data ichave yakachengetwa.
Munguva yekuyedza, uchishandisa iyo cache yemukati yekuona maitiro FLUSH + RELOAD, ivo vaongorori vakakwanisa kuronga chiteshi yekufambisa kweyakavanzika data ku kumhanya kwemakumi mashanu nesere pasekondi.
Iwo iwo matekinoroji ayo anobatsira kuvharidzira kurwisa kweMeltdown, senge kushandisa rairo dzeLFENCE, inogona kushandiswa kudzivirira pakurwisa kutsva.
Panguva imwecheteyo, vaongorori vanoona kuti, Kuenzaniswa neIntel processors, iyo dhizaini yeA processorMD inogumira mukana wekurwiswa chaiko, asi haibatanidze kushandiswa kwenzira nyowani mukubatana pamwe nekumwe kurwisa kwema microarchitectural kuwedzera kushanda kwayo.
Kunyanya, sarudzo inorwiswa yekurwisa haibvumidze kuona zvirimo zvekernel ndangariro nzvimbo nedzimwe nzira, asi inogumira pakukwanisa kuwana dzimwe tambo dzechirongwa chimwe chete icho chiri kumhanya mune imwecheteyo memory memory nzvimbo.
mabviro: https://www.amd.com, https://arxiv.org/