Gulu la ofufuza ochokera ku Technical University of Graz (Austria) ndi Helmholtz Center for Information Security (CISPA) awululira za chiopsezo (CVE-2021-26318) mu mapurosesa onse a AMD omwe amapangitsa kuti zitheke kuchita mbali ya Meltdown-class- kuwukira kwanjira (poyamba zinkaganiziridwa kuti mapurosesa a AMD sakhudzidwa ndi chiwopsezo cha Meltdown). Mwachidziwitso, kuwukirako kungagwiritsidwe ntchito kukhazikitsa njira zoyankhulirana zobisika, kuyang'anira zochitika mu kernel, kapena kupeza zambiri za ma adilesi omwe ali mu kernel memory kuti adutse chitetezo cha KASLR pomwe akugwiritsa ntchito zofooka mu kernel.
AMD imawona kuti sikoyenera kuchitapo kanthu kuti aletse vutoli, chifukwa chiwopsezocho, monga kuukira kofananako komwe kunapezeka mu Ogasiti, sichitha kugwiritsidwa ntchito m'malo enieni, kumachepetsedwa ndi malire apano a malo adilesi ndipo kumafuna kukhalapo kwa ena. malangizo okonzeka opangidwa (zida) mu kernel. Kuti awonetse kuukiraku, ofufuzawo adanyamula gawo lawo la kernel ndi chida chowonjezera mwachinyengo. Muzochitika zenizeni, owukira atha kugwiritsa ntchito, mwachitsanzo, kuwonekera pachiwopsezo nthawi zonse mu gawo la eBPF kuti m'malo mwazotsatira zofunika.
Kuteteza ku mtundu watsopanowu, AMD idalimbikitsa kugwiritsa ntchito njira zotetezedwa zomwe zimathandizira kuletsa kuukira kwa Meltdown, monga kugwiritsa ntchito malangizo a LFENCE. Ofufuza omwe adazindikira vutoli amalimbikitsa kuti azitha kudzipatula patebulo lokumbukira (KPTI), lomwe m'mbuyomu linkangogwiritsidwa ntchito pa ma processor a Intel.
Pakuyesa, ofufuzawo adakwanitsa kutulutsa zambiri kuchokera ku kernel kupita kumalo ogwiritsira ntchito pa liwiro la 52 byte pamphindikati, poganizira kukhalapo kwa chida mu kernel chomwe chimagwira ntchitoyo "ngati (offset <data_len) tmp = LUT[deta[offset] * 4096];” . Pali njira zingapo zomwe zaperekedwa zopezeranso zambiri kudzera m'makanema am'mbali omwe amathera mu cache panthawi yongopeka. Njira yoyamba imachokera pa kusanthula zopotoka mu nthawi yoperekera malangizo a purosesa "PREFETCH" (Prefetch + Time), ndipo yachiwiri pakusintha kusintha kwa mphamvu yogwiritsira ntchito mphamvu pochita "PREFETCH" (Prefetch + Power).
Kumbukirani kuti chiwopsezo chambiri cha Meltdown chimachokera ku mfundo yakuti panthawi yongoganizira za malangizo, purosesa imatha kupeza malo achinsinsi ndikutaya zotsatira zake, chifukwa mwayi wokhazikitsidwa umaletsa mwayi woterewu kuchokera kwa wogwiritsa ntchito. Mu pulogalamuyi, chipika chongophedwa mongopeka chimalekanitsidwa ndi code yayikulu ndi nthambi yokhazikika, yomwe nthawi zonse imayaka moto, koma chifukwa chakuti mawu okhazikika amagwiritsira ntchito mtengo wowerengeka womwe purosesa sakudziwa panthawi yoyeserera. kachidindo, zosankha zonse za nthambi zimachitika mongoganizira.
Popeza kuti ntchito zomwe zimachitidwa mongopeka zimagwiritsa ntchito cache yomweyo monga momwe amachitira malangizo, ndizotheka panthawi yongopeka kuyika zolembera mu cache zomwe zikuwonetsa zomwe zili m'malo okumbukira achinsinsi, ndiyeno pama code omwe amachitidwa kuti adziwe mtengo wake kudzera munthawi yake. kusanthula kumafikira ku data yosungidwa komanso yosasungidwa.
Source: opennet.ru