{"id":100574,"date":"2021-06-22T16:24:20","date_gmt":"2021-06-22T14:24:20","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimosti-v-podsisteme-ebpf-pozvolyayushhie-obojti-zashhitu-ot-atak-klassa-spectre"},"modified":"2021-06-22T16:24:20","modified_gmt":"2021-06-22T14:24:20","slug":"uyazvimosti-v-podsisteme-ebpf-pozvolyayushhie-obojti-zashhitu-ot-atak-klassa-spectre","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/news\/uyazvimosti-v-podsisteme-ebpf-pozvolyayushhie-obojti-zashhitu-ot-atak-klassa-spectre","title":{"rendered":"Zranitelnosti v subsyst\u00e9mu eBPF, kter\u00e9 umo\u017e\u0148uj\u00ed obch\u00e1zen\u00ed ochrany proti \u00fatok\u016fm t\u0159\u00eddy Spectre.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

V j\u00e1d\u0159e Linux byla zji\u0161t\u011bna zranitelnost (CVE-2021-33624), kter\u00e1 umo\u017e\u0148uje vyu\u017eit\u00ed subsyst\u00e9mu eBPF k obch\u00e1zen\u00ed ochrany v\u016f\u010di zranitelnostem typu Spectre, co\u017e d\u00e1v\u00e1 mo\u017enost ur\u010dit obsah pam\u011bti v d\u016fsledku vytvo\u0159en\u00ed podm\u00ednek pro spekulativn\u00ed vykon\u00e1v\u00e1n\u00ed ur\u010dit\u00fdch operac\u00ed. K \u00fatoku Spectre je pot\u0159eba p\u0159\u00edtomnost ur\u010dit\u00e9 sekvence p\u0159\u00edkaz\u016f v privilegovan\u00e9m k\u00f3du, kter\u00e9 vedou k spekulativn\u00edmu vykon\u00e1v\u00e1n\u00ed instrukc\u00ed. Manipulac\u00ed s p\u0159ed\u00e1van\u00fdmi BPF programy lze generovat podobn\u00e9 instrukce v eBPF a dos\u00e1hnout \u00faniku obsahu j\u00e1drov\u00e9 pam\u011bti a libovoln\u00fdch oblast\u00ed fyzick\u00e9 pam\u011bti prost\u0159ednictv\u00edm bo\u010dn\u00edch kan\u00e1l\u016f. <\/p>\n

Zranitelnost je zp\u016fsobena nedostatky v ov\u011b\u0159ova\u010di, kter\u00fd se pou\u017e\u00edv\u00e1 k identifikaci chyb a nep\u0159ijateln\u00e9 aktivity v programech BPF. Ov\u011b\u0159ova\u010d proch\u00e1z\u00ed mo\u017en\u00e9 cesty prov\u00e1d\u011bn\u00ed k\u00f3du, ale vynech\u00e1v\u00e1 v\u011btvic\u00ed mo\u017enosti, kter\u00e9 jsou z pohledu semantiky architektury instruk\u010dn\u00edho souboru nep\u0159ijateln\u00e9. P\u0159i prov\u00e1d\u011bn\u00ed programu BPF mohou b\u00fdt takov\u00e9 v\u011btvic\u00ed mo\u017enosti, kter\u00e9 ov\u011b\u0159ova\u010d nezohlednil, nespr\u00e1vn\u011b p\u0159edpov\u011bzeny procesorem a provedeny spekulativn\u00edm zp\u016fsobem. Nap\u0159\u00edklad p\u0159i anal\u00fdze operace \u201eload\u201c ov\u011b\u0159ova\u010d p\u0159edpokl\u00e1d\u00e1, \u017ee v instrukci je pou\u017eit registr s adresou, jej\u00ed\u017e hodnota je v\u017edy v dan\u00fdch mez\u00edch, ale \u00fato\u010dn\u00edk m\u016f\u017ee vytvo\u0159it podm\u00ednky, za kter\u00fdch se procesor pokus\u00ed spekulativn\u011b prov\u00e9st operaci s adresou, kter\u00e1 nespl\u0148uje podm\u00ednky kontroly. <\/p>\n

Probl\u00e9m se projevuje po\u010d\u00ednaje verz\u00ed j\u00e1dra 4.15 a byl odstran\u011bn ve form\u011b patch\u016f (1, 2, 3, 4). V distribuc\u00edch z\u016fst\u00e1v\u00e1 zranitelnost zat\u00edm neopraven\u00e1 (Debian, RHEL, Ubuntu, Fedora, SUSE, Arch). <\/p>\n

D\u00e1le lze zm\u00ednit pozn\u00e1mku o vlivu na v\u00fdkon prost\u0159edk\u016f na ochranu proti zranitelnostem typu Spectre. V pozn\u00e1mce jsou shrnuty v\u00fdsledky optimalizace debuggeru rr (Record and Replay), kter\u00fd byl vytvo\u0159en v Mozille pro lad\u011bn\u00ed slo\u017eit\u011b reprodukovateln\u00fdch chyb ve Firefoxu. Ke\u0161ov\u00e1n\u00ed syst\u00e9mov\u00fdch vol\u00e1n\u00ed, pou\u017e\u00edvan\u00fdch k ov\u011b\u0159en\u00ed existence adres\u00e1\u0159\u016f, umo\u017enilo zkr\u00e1tit dobu prov\u00e1d\u011bn\u00ed operace \u201err sources\u201c pro testovac\u00ed projekt z 3 minut 19 sekund na 36 sekund. <\/p>\n

Autor optimalizace se rozhodl zkontrolovat, jak se zm\u011bn\u00ed v\u00fdkon po vypnut\u00ed ochrany proti Spectre. Po na\u010dten\u00ed syst\u00e9mu s parametrem \u201emitigations=off\u201c byla doba prov\u00e1d\u011bn\u00ed \u201err sources\u201c bez optimalizace 2 minuty 5 sekund (o 1,6x rychlej\u0161\u00ed), zat\u00edmco s optimalizac\u00ed \u2014 33 sekund (o 9% rychlej\u0161\u00ed). Zaj\u00edmav\u00e9 je, \u017ee vypnut\u00ed ochrany proti Spectre nejen \u017ee zkr\u00e1tilo dobu prov\u00e1d\u011bn\u00ed k\u00f3du na \u00farovni j\u00e1dra (z 2m9s na 1m32s o 1,4x), ale tak\u00e9 dvakr\u00e1t sn\u00ed\u017eilo dobu prov\u00e1d\u011bn\u00ed v u\u017eivatelsk\u00e9m prostoru (z 1m9s na 0m33s), pravd\u011bpodobn\u011b kv\u016fli sn\u00ed\u017een\u00ed \u00fa\u010dinnosti pr\u00e1ce CPU cache a resetov\u00e1n\u00ed TLB p\u0159i zapnut\u00e9 ochrann\u011b proti Spectre.
\n
Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0412 \u044f\u0434\u0440\u0435 Linux \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2021-33624), \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0430\u044f \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u044c \u043f\u043e\u0434\u0441\u0438\u0441\u0442\u0435\u043c\u0443 \u0435BPF \u0434\u043b\u044f \u043e\u0431\u0445\u043e\u0434\u0430 \u0437\u0430\u0449\u0438\u0442\u044b \u043e\u0442 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439 \u043a\u043b\u0430\u0441\u0441\u0430 Spectre, \u0434\u0430\u044e\u0449\u0438\u0445 \u0432\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u044c \u043e\u043f\u0440\u0435\u0434\u0435\u043b\u0438\u0442\u044c \u0441\u043e\u0434\u0435\u0440\u0436\u0438\u043c\u043e\u0435 \u043f\u0430\u043c\u044f\u0442\u0438 \u0432 \u0440\u0435\u0437\u0443\u043b\u044c\u0442\u0430\u0442\u0435 \u0441\u043e\u0437\u0434\u0430\u043d\u0438\u044f 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[…]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-100574","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Zranitelnosti v subsyst\u00e9mu eBPF, kter\u00e9 umo\u017e\u0148uj\u00ed obch\u00e1zet ochranu proti \u00fatok\u016fm typu Spectre | ProHoster","description":"V j\u00e1d\u0159e Linux byla zji\u0161t\u011bna zranitelnost (CVE-2021-33624), kter\u00e1 umo\u017e\u0148uje vyu\u017e\u00edt subsyst\u00e9m eBPF k obch\u00e1zen\u00ed ochrany p\u0159ed zranitelnostmi typu Spectre, co\u017e umo\u017e\u0148uje ur\u010dit obsah 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