Ithimba labacwaningi abavela e-Technical University of Graz (Austria) kanye ne-Helmholtz Centre for Information Security (CISPA) badalule ubungozi (CVE-2021-26318) kuwo wonke ama-AMD processors okwenza kube nokwenzeka ukwenza uhlangothi lwe-Meltdown-class- ukuhlaselwa kwesiteshi (ekuqaleni bekucatshangwa ukuthi amaphrosesa e-AMD awathintwa ukuba sengozini kwe-Meltdown). Ngokwezinto ezibonakalayo, ukuhlasela kungasetshenziswa ukusungula iziteshi zokuxhumana ezicashile, ukuqapha umsebenzi ku-kernel, noma ukuthola ulwazi mayelana namakheli kumemori ye-kernel ukuze kudlule ukuvikelwa kwe-KASLR kuyilapho kuxhashazwa ubuthakathaka ku-kernel.
I-AMD ikubona njengokungafanele ukuthatha izinyathelo ezikhethekile zokuvimba inkinga, njengoba ubungozi, njengokuhlasela okufanayo okutholwe ngo-Agasti, akusebenzi kangako ezimweni zangempela, kunqunyelwe imingcele yamanje yendawo yekheli lenqubo futhi kudinga ukuba khona kokuthile. ukulandelana okwenziwe ngomumo kwemiyalelo (amagajethi) ku-kernel. Ukukhombisa ukuhlasela, abacwaningi balayishe imojula yabo ye-kernel ngegajethi engezwe ngokwenziwa. Ezimweni zangempela, abahlaseli bangasebenzisa, isibonelo, ukuvela kobungozi njalo kusistimu engaphansi ye-eBPF ukuze bamiselele ukulandelana okudingekayo.
Ukuze uvikeleke kulolu hlobo olusha lokuhlasela, i-AMD yatusa ukusebenzisa amasu okubhala amakhodi avikelekile asiza ukuvimba ukuhlasela kwe-Meltdown, njengokusebenzisa imiyalelo ye-LFENCE. Abacwaningi abahlonze inkinga batusa ukunika amandla ukuhlukaniswa kwetafula lememori eqinile (i-KPTI), ngaphambilini ebisetshenziselwa ama-Intel processors kuphela.
Ngesikhathi sokuhlolwa, abacwaningi bakwazile ukuvuza ulwazi kusuka ku-kernel kuya ohlelweni lomsebenzisi ngesivinini samabhayithi angu-52 ngomzuzwana, uma kubhekwa ukuba khona kwegajethi ku-kernel eyenza umsebenzi "uma (offset < data_len) tmp = LUT[idatha[offset] *4096];” Kuphakanyiswe izindlela ezimbalwa zokubuyisa ulwazi ngamashaneli aseceleni agcina esenqolobaneni ngesikhathi sokubulawa okucatshangelwayo. Indlela yokuqala isuselwe ekuhlaziyeni ukuchezuka ngesikhathi sokwenziwa komyalelo wokucubungula "PREFETCH" (Prefetch+Time), kanti eyesibili ekuguquleni ushintsho ekusetshenzisweni kwamandla lapho kusetshenziswa okuthi "PREFETCH" (Prefetch+Power).
Khumbula ukuthi ukuba sengozini kwe-Meltdown yakudala kusekelwe eqinisweni lokuthi ngesikhathi sokwenziwa kokuqagela kwemiyalelo, iphrosesa ingakwazi ukufinyelela indawo yedatha eyimfihlo bese ilahla umphumela, njengoba amalungelo amisiwe avimbela ukufinyelela okunjalo kusukela kunqubo yomsebenzisi. Kulolu hlelo, ibhulokhi eyenziwe ngokuqagela ihlukaniswa nekhodi eyinhloko yigatsha elinemibandela, elihlala livutha ezimweni zangempela, kodwa ngenxa yokuthi isitatimende esinemibandela sisebenzisa inani elibaliwe umprosesa angalazi ngesikhathi sokukhishwa kwangaphambili. ikhodi, zonke izinketho zegatsha zenziwa ngokuqagela.
Njengoba imisebenzi eyenziwe ngokuqagela isebenzisa inqolobane efanayo njengemiyalelo evame ukukhishwa, kungenzeka ngesikhathi sokuqagela ukusetha omaka kunqolobane ebonisa okuqukethwe kwezingcezu ngazinye endaweni yenkumbulo eyimfihlo, bese kukhodi esanda kukhishwa ukuze kunqunywe inani lazo ngokusebenzisa isikhathi. Ukuhlaziya kufinyelela kudatha egcinwe kunqolobane nengagciniwe.
Source: opennet.ru