{"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\/pt\/blog\/news\/plany-po-usileniyu-mehanizma-zashhity-w-x-v-openbsd","title":{"rendered":"Planos para fortalecer o mecanismo de prote\u00e7\u00e3o W^X no OpenBSD","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Theo de Raad <noindex><a rel=\"nofollow\" href=\"https:\/\/marc.info\/?l=openbsd-tech&#038;m=155899373514678&#038;w=2\">compartilhou<\/a><\/noindex> planos para refor\u00e7ar o mecanismo de prote\u00e7\u00e3o de mem\u00f3ria W^X (Write XOR Execute). A ess\u00eancia do mecanismo \u00e9 que as p\u00e1ginas de mem\u00f3ria de um processo n\u00e3o podem ser acessadas simultaneamente para grava\u00e7\u00e3o e execu\u00e7\u00e3o. Assim, o c\u00f3digo s\u00f3 pode ser executado ap\u00f3s a proibi\u00e7\u00e3o de grava\u00e7\u00e3o, e a grava\u00e7\u00e3o em uma p\u00e1gina de mem\u00f3ria s\u00f3 \u00e9 poss\u00edvel ap\u00f3s a proibi\u00e7\u00e3o de execu\u00e7\u00e3o. O mecanismo W^X ajuda a proteger aplicativos no espa\u00e7o do usu\u00e1rio contra ataques t\u00edpicos realizados atrav\u00e9s de estouro de buffer, incluindo estouros de pilha, e est\u00e1 ativo no OpenBSD. <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=44506\">padr\u00e3o<\/a><\/noindex>.<\/p>\n<p>Desde o in\u00edcio do trabalho sobre o W^X, ficou claro que \u00e9 um caminho longo, pois existe um n\u00famero significativo de aplicativos que utilizam JIT. As implementa\u00e7\u00f5es de JIT podem ser divididas em tr\u00eas categorias:<\/p>\n<ul>\n<li class=\"l\"> Alternando a mem\u00f3ria entre os estados W e X, aceitando o &#171;custo&#187; da chamada de sistema. <noindex><a rel=\"nofollow\" href=\"https:\/\/man.openbsd.org\/mprotect.2\">mprotect<\/a><\/noindex>.\n<li class=\"l\"> Criando aliases entre um par de mapeamentos W e X da mesma mem\u00f3ria.\n<li class=\"l\"> A variante mais &#171;sujar&#187; \u2014 modelos de mem\u00f3ria W|X que permitem a grava\u00e7\u00e3o e execu\u00e7\u00e3o simult\u00e2neas.\n<\/ul>\n<p>Atualmente, h\u00e1 significativamente menos programas utilizando a terceira variante e mais usando a primeira e a segunda. No entanto, como era necess\u00e1rio rodar programas com W|X JIT (principalmente o Chromium e o Iridum), foi adicionada a op\u00e7\u00e3o de montar o sistema de arquivos &#171;wxallowed&#187;, que permitia usar a mem\u00f3ria simultaneamente para grava\u00e7\u00e3o e execu\u00e7\u00e3o, caso o arquivo ELF execut\u00e1vel estivesse marcado com o marcador &#171;wxneeded&#187;, e os pr\u00f3prios aplicativos fossem adicionalmente protegidos utilizando mecanismos. <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=43295\">pledge<\/a><\/noindex> e <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=49042\">unveil<\/a><\/noindex> para restringir a lista de chamadas de sistema utilizadas e as partes do sistema de arquivos dispon\u00edveis para o aplicativo, respectivamente.<\/p>\n<p>Para dificultar ainda mais a explora\u00e7\u00e3o de vulnerabilidades em tais aplicativos, foi proposta uma adi\u00e7\u00e3o ao mecanismo <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=48243\">MAP_STACK<\/a><\/noindex>, que verifica se a chamada de sistema est\u00e1 sendo executada a partir de uma p\u00e1gina de mem\u00f3ria dispon\u00edvel para grava\u00e7\u00e3o. Se a p\u00e1gina estiver dispon\u00edvel para grava\u00e7\u00e3o, o processo \u00e9 encerrado for\u00e7adamente. Assim, o invasor n\u00e3o conseguir\u00e1 utilizar chamadas de sistema e ser\u00e1 for\u00e7ado a tentar encontrar os gadgets necess\u00e1rios na implementa\u00e7\u00e3o JIT ou at\u00e9 mesmo realizar um trabalho mais dif\u00edcil de detectar ganchos de chamadas de sistema diretamente dentro <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=44320\">do libc aleatoriamente vinculado.<\/a><\/noindex>. <\/p>\n<p>Os processos Chrome\/Iridium s\u00e3o suficientemente protegidos atrav\u00e9s de pledge e unveil, mas a proibi\u00e7\u00e3o de usar, por exemplo, a chamada de sistema write(2) claramente traz algumas vantagens, pois cria dificuldades adicionais para o atacante. No entanto, dificuldades tamb\u00e9m podem surgir se a implementa\u00e7\u00e3o do JIT utilizar chamadas de sistema nativas a partir da mem\u00f3ria W|X. Contudo, h\u00e1 raz\u00f5es para acreditar que n\u00e3o enfrentaremos tal situa\u00e7\u00e3o, j\u00e1 que a ABI foi alterada v\u00e1rias vezes, mas ningu\u00e9m nunca relatou problemas.<\/p>\n<p>As mudan\u00e7as j\u00e1 est\u00e3o dispon\u00edveis nas vers\u00f5es regulares da ramifica\u00e7\u00e3o OpenBSD-CURRENT, e todos os interessados s\u00e3o convidados a test\u00e1-las.<\/p>\n<p>Coment\u00e1rios individuais foram feitos por Theo sobre as not\u00edcias relacionadas ao modo de funcionamento do Chrome\/Iridium <noindex><a rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=50559\">JITless<\/a><\/noindex>. Do seu ponto de vista, isso \u00e9 aceit\u00e1vel para alguns modelos de uso, mas provavelmente n\u00e3o para todos, pois nesse modo a carga no processador aumentar\u00e1 evidentemente. Agora, o Chrome funcionar\u00e1 principalmente se &#171;wxallowed&#187; for desativado para \/usr\/local, embora possam ocorrer problemas com algumas extens\u00f5es (cita-se o ghostery como exemplo). De qualquer forma, Theo espera que a opera\u00e7\u00e3o completa em modo JITless seja aprimorada para um estado totalmente funcional em breve.<\/p>\n<p><noindex><a rel=\"nofollow\" name=\"link\"><\/a><\/noindex><\/p>\n<p>Fonte: <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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