{"id":34721,"date":"2019-10-31T22:00:00","date_gmt":"2019-10-31T19:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/plany-po-usileniyu-mehanizma-zashhity-w-x-v-openbsd\/"},"modified":"2019-10-31T22:00:00","modified_gmt":"2019-10-31T19:00:00","slug":"plany-po-usileniyu-mehanizma-zashhity-w-x-v-openbsd","status":"publish","type":"post","link":"https:\/\/prohoster.info\/da\/blog\/news\/plany-po-usileniyu-mehanizma-zashhity-w-x-v-openbsd","title":{"rendered":"Planer for at styrke W^X-beskyttelsesmekanismen i OpenBSD","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Theo De Raadt <noindex><a rel=\"nofollow\" href=\"https:\/\/marc.info\/?l=openbsd-tech&#038;m=155899373514678&#038;w=2\">har delt<\/a><\/noindex> planer for at styrke W^X (Write XOR Execute) hukommelsesbeskyttelsesmekanismen. Essensen af mekanismen er, at hukommelsessiderne i processen ikke kan v\u00e6re tilg\u00e6ngelige for b\u00e5de skrivning og udf\u00f8relse p\u00e5 samme tid. P\u00e5 den m\u00e5de kan koden kun udf\u00f8res efter at skriveadgang er blevet forbudt, og skrivning til hukommelsessiden er kun mulig efter udf\u00f8relsen er forbudt. W^X-mekanismen hj\u00e6lper med at beskytte applikationer i brugerrummet mod typiske angreb, der udf\u00f8res gennem buffer overflow, herunder stak overflow, og den er aktiv i OpenBSD <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=44506\">som standard<\/a><\/noindex>.<\/p>\n<p>Fra begyndelsen af arbejdet med W^X var det klart, at det ville v\u00e6re en lang rejse, da der findes et betydeligt antal applikationer, der bruger JIT. JIT-implementeringer kan opdeles i tre kategorier:<\/p>\n<ul>\n<li class=\"l\"> Skiftende hukommelse mellem W- og X-tilstande, idet man accepterer &#171;omkostningen&#187; ved systemkaldet <noindex><a rel=\"nofollow\" href=\"https:\/\/man.openbsd.org\/mprotect.2\">mprotect<\/a><\/noindex>.\n<li class=\"l\"> Opretter aliasser mellem et par af W og X kortl\u00e6gninger af den samme hukommelse.\n<li class=\"l\"> Den mest &#171;beskidte&#187; variant \u2014 kr\u00e6vende hukommelsesmodeller W|X, der tillader samtidig skrivning og udf\u00f8relse.\n<\/ul>\n<p>I \u00f8jeblikket er der betydeligt f\u00e6rre programmer, der bruger den tredje variant, og flere der bruger den f\u00f8rste og anden. Ikke desto mindre, da det var n\u00f8dvendigt at k\u00f8re programmer med W|X JIT (prim\u00e6rt Chromium og Iridium), blev der tilf\u00f8jet en mulighed for at montere filsystemet &#171;wxallowed&#187;, som gjorde det muligt at bruge hukommelsen til b\u00e5de skrivning og udf\u00f8relse, hvis den udf\u00f8rbare ELF-fil var markeret med &#171;wxneeded&#187;, og selve applikationerne blev yderligere beskyttet ved hj\u00e6lp af mekanismer. <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=43295\">pledge<\/a><\/noindex> og <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=49042\">unveil<\/a><\/noindex> for at begr\u00e6nse listen over anvendte systemopkald og de dele af filsystemet, der er tilg\u00e6ngelige for applikationen.<\/p>\n<p>For yderligere at komplicere udnyttelsen af s\u00e5rbarheder i s\u00e5danne applikationer er der foresl\u00e5et en tilf\u00f8jelse til mekanismen <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=48243\">MAP_STACK<\/a><\/noindex>, som kontrollerer, om systemopkaldet udf\u00f8res fra en skrivbar hukommelsesside. Hvis siden er tilg\u00e6ngelig for skrivning, afsluttes processen tvangsm\u00e6ssigt. P\u00e5 den m\u00e5de kan en angriber ikke bruge systemopkald og vil v\u00e6re n\u00f8dt til at fors\u00f8ge at finde de n\u00f8dvendige gadgets i JIT-implementeringen eller endda udf\u00f8re det h\u00e5rdere arbejde med at opdage stub-systemopkald direkte indeni. <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=44320\">tilf\u00e6ldig relateret libc<\/a><\/noindex>. <\/p>\n<p>Chrome\/Iridium-processerne er allerede ret sikkert beskyttede ved hj\u00e6lp af pledge og unveil, men at fjerne muligheden for at bruge for eksempel systemopkaldet write(2) har \u00e5benlyst nogle fordele, da det skaber yderligere vanskeligheder for angriberen. Dog kan der opst\u00e5 problemer, hvis JIT-implementeringen bruger native systemopkald fra W|X-hukommelsen. Der er imidlertid grund til at h\u00e5be, at man ikke vil st\u00f8de p\u00e5 s\u00e5danne problemer, da ABI er blevet \u00e6ndret flere gange, men ingen har nogensinde rapporteret om problemer.<\/p>\n<p>\u00c6ndringerne er allerede tilg\u00e6ngelige i de regelm\u00e6ssige snapshots fra OpenBSD - Current-grenen, alle interesserede er inviteret til at teste.<\/p>\n<p>Teo fortjente en s\u00e6rlig kommentar ang\u00e5ende nyheden om tilf\u00f8jelsen af en tilstand i Chrome\/Iridium <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=50559\">JITless<\/a><\/noindex>. Set fra dette perspektiv er det acceptabelt for nogle anvendelsesm\u00f8nstre, men sandsynligvis ikke for alle, da belastningen p\u00e5 processoren \u00e5benlyst vil stige i denne tilstand. I \u00f8jeblikket vil Chrome prim\u00e6rt fungere, hvis &#171;wxallowed&#187; er deaktiveret for \/usr\/local, selvom der kan opst\u00e5 problemer med nogle udvidelser (som f.eks. Ghostery). Uanset hvad, h\u00e5ber Theo, at den fulde funktionalitet i JITless-tilstand vil blive f\u00e6rdiggjort og blive helt operationel snart.<\/p>\n<p><noindex><a rel=\"nofollow\" name=\"link\"><\/a><\/noindex><\/p>\n<p>Kilde: <a \ncontent=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=50763\">opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0422\u0435\u043e \u0414\u0435 \u0420\u0430\u0430\u0434\u0442 \u043f\u043e\u0434\u0435\u043b\u0438\u043b\u0441\u044f \u043f\u043b\u0430\u043d\u0430\u043c\u0438 \u043f\u043e \u0443\u0441\u0438\u043b\u0435\u043d\u0438\u044e \u043c\u0435\u0445\u0430\u043d\u0438\u0437\u043c\u0430 \u0437\u0430\u0449\u0438\u0442\u044b \u043f\u0430\u043c\u044f\u0442\u0438 W^X (Write XOR Execute). \u0421\u0443\u0442\u044c \u043c\u0435\u0445\u043d\u0438\u0437\u043c\u0430 \u0432 \u0442\u043e\u043c, \u0447\u0442\u043e \u0441\u0442\u0440\u0430\u043d\u0438\u0446\u044b \u043f\u0430\u043c\u044f\u0442\u0438 \u043f\u0440\u043e\u0446\u0435\u0441\u0441\u0430 \u043d\u0435 \u043c\u043e\u0433\u0443\u0442 \u0431\u044b\u0442\u044c \u043e\u0434\u043d\u043e\u0432\u0440\u0435\u043c\u0435\u043d\u043d\u043e \u0434\u043e\u0441\u0442\u0443\u043f\u043d\u044b \u043d\u0430 \u0437\u0430\u043f\u0438\u0441\u044c \u0438 \u0438\u0441\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u0435. \u0422\u0430\u043a\u0438\u043c \u043e\u0431\u0440\u0430\u0437\u043e\u043c, \u043a\u043e\u0434 \u043c\u043e\u0436\u0435\u0442 \u0431\u044b\u0442\u044c \u0438\u0441\u043f\u043e\u043b\u043d\u0435\u043d \u0442\u043e\u043b\u044c\u043a\u043e \u043f\u043e\u0441\u043b\u0435 \u0437\u0430\u043f\u0440\u0435\u0449\u0435\u043d\u0438\u044f \u0437\u0430\u043f\u0438\u0441\u0438, \u0430 \u0437\u0430\u043f\u0438\u0441\u044c \u0432 \u0441\u0442\u0440\u0430\u043d\u0438\u0446\u0443 \u043f\u0430\u043c\u044f\u0442\u0438 \u0432\u043e\u0437\u043c\u043e\u0436\u043d\u0430 \u0442\u043e\u043b\u044c\u043a\u043e \u043f\u043e\u0441\u043b\u0435 \u0437\u0430\u043f\u0440\u0435\u0442\u0430 \u0438\u0441\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u044f. \u041c\u0435\u0445\u0430\u043d\u0438\u0437\u043c W^X \u043f\u043e\u043c\u043e\u0433\u0430\u0435\u0442 \u0437\u0430\u0449\u0438\u0442\u0438\u0442\u044c [&hellip;]<\/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-34721","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.3 - aioseo.com -->\n\t<meta name=\"description\" content=\"\u0422\u0435\u043e \u0414\u0435 \u0420\u0430\u0430\u0434\u0442 \u043f\u043e\u0434\u0435\u043b\u0438\u043b\u0441\u044f \u043f\u043b\u0430\u043d\u0430\u043c\u0438 \u043f\u043e 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