{"id":121698,"date":"2025-02-04T09:46:00","date_gmt":"2025-02-04T07:46:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimost-v-zagruzchike-mikrokoda-v-cpu-amd-pozvolyayushhaya-obojti-izolyacziyu-sev-snp"},"modified":"2025-02-04T09:46:00","modified_gmt":"2025-02-04T07:46:00","slug":"uyazvimost-v-zagruzchike-mikrokoda-v-cpu-amd-pozvolyayushhaya-obojti-izolyacziyu-sev-snp","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/news\/uyazvimost-v-zagruzchike-mikrokoda-v-cpu-amd-pozvolyayushhaya-obojti-izolyacziyu-sev-snp","title":{"rendered":"Vulnerabilidade no carregador de microc\u00f3digo da CPU AMD que permite contornar a isola\u00e7\u00e3o SEV-SNP","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Pesquisadores de seguran\u00e7a da Google publicaram informa\u00e7\u00f5es sobre uma vulnerabilidade (CVE-2024-56161) nos processadores AMD, que afeta o carregador de microc\u00f3digo e permite contornar o mecanismo de verifica\u00e7\u00e3o de assinatura digital durante as atualiza\u00e7\u00f5es de microc\u00f3digo. O carregamento de microc\u00f3digo modificado permite comprometer o mecanismo AMD SEV (Secure Encrypted Virtualization), utilizado em sistemas de virtualiza\u00e7\u00e3o para proteger m\u00e1quinas virtuais contra interven\u00e7\u00f5es do hipervisor ou do administrador do sistema host. <\/p>\n

A vulnerabilidade \u00e9 causada pelo uso de uma fun\u00e7\u00e3o hash insegura no c\u00f3digo que realiza a verifica\u00e7\u00e3o da assinatura digital ap\u00f3s o carregamento do microc\u00f3digo na CPU. Para realizar o ataque, \u00e9 necess\u00e1rio ter privil\u00e9gios de administrador no sistema local (com a capacidade de executar c\u00f3digo no n\u00edvel zero de prote\u00e7\u00e3o (ring0), estando fora de uma m\u00e1quina virtual). <\/p>\n

Durante o ataque, \u00e9 poss\u00edvel interferir no funcionamento de sistemas convidados protegidos por meio das extens\u00f5es AMD SEV (Secure Encrypted Virtualization) e SEV-SNP (Secure Nested Paging), que oferecem garantias de integridade da mem\u00f3ria. m\u00e1quinas virtuais<\/a>, isolando os registradores do processador e garantindo funcionamento seguro com tabelas de p\u00e1ginas de mem\u00f3ria aninhadas. O mecanismo AMD SEV foi criado para que o pessoal dos datacenters e provedores de nuvem n\u00e3o conseguisse alterar ou analisar o conte\u00fado da mem\u00f3ria de sistemas convidados protegidos, bem como distorcer c\u00e1lculos. <\/p>\n

Os pesquisadores prepararam um prot\u00f3tipo de exploit que permite carregar microc\u00f3digo arbitr\u00e1rio na CPU, n\u00e3o assinado digitalmente. Para demonstrar o perigo da vulnerabilidade, foi proposta uma atualiza\u00e7\u00e3o de microc\u00f3digo que altera a l\u00f3gica da instru\u00e7\u00e3o RDRAND, usada como uma das fontes de entropia em geradores de n\u00fameros aleat\u00f3rios pseudo-aleat\u00f3rios, utilizados no processo de forma\u00e7\u00e3o de chaves, na execu\u00e7\u00e3o de opera\u00e7\u00f5es criptogr\u00e1ficas e para a gera\u00e7\u00e3o de identificadores aleat\u00f3rios. <\/p>\n

A altera\u00e7\u00e3o leva ao retorno do comando RDRAND apenas com o n\u00famero 4, em vez de uma sequ\u00eancia aleat\u00f3ria. Para prevenir ataques reais a sistemas de computa\u00e7\u00e3o confidencial, o microc\u00f3digo modificado zera o sinal CF (carry flag), ou seja, marca o valor emitido como errado. Detalhes adicionais e ferramentas para gerar o microc\u00f3digo alterado est\u00e3o previstas para serem publicadas em 5 de mar\u00e7o, para dar aos usu\u00e1rios tempo para instalar a corre\u00e7\u00e3o em seus sistemas. Um exemplo bem-sucedido de ataque foi demonstrado para servidores<\/a> com os processadores AMD EPYC 7B13 (Milan) e AMD Ryzen 9 7940HS (Phoenix). <\/p>\n

No relat\u00f3rio da AMD, \u00e9 apontado que a vulnerabilidade se manifesta nos processadores AMD baseados nas gera\u00e7\u00f5es 1-4 da microarquitetura Zen. A atualiza\u00e7\u00e3o do microc\u00f3digo que corrige a vulnerabilidade foi lan\u00e7ada em 13 de dezembro de 2024 para os processadores das s\u00e9ries AMD EPYC 7001, 7002 e 7003 (Naples, Rome, Milan e Milan-X), e em 16 de dezembro para os processadores da s\u00e9rie AMD EPYC 9004 (Genoa, Genoa-X e Bergamo\/Siena). Para corrigir a vulnerabilidade em sistemas que utilizam a certifica\u00e7\u00e3o SEV-SNP, uma atualiza\u00e7\u00e3o adicional do firmware AMD SEV (fornecida junto com as atualiza\u00e7\u00f5es de BIOS dos fabricantes de hardware) \u00e9 necess\u00e1ria. <\/p>\n

Al\u00e9m disso, foi relatada outra vulnerabilidade em processadores AMD que permite a execu\u00e7\u00e3o de um ataque por canal lateral para extrair informa\u00e7\u00f5es sobre c\u00e1lculos em sistemas virtuais protegidos usando o mecanismo AMD SEV. O problema afeta as gera\u00e7\u00f5es 1-4 dos processadores AMD EPYC e est\u00e1 relacionado \u00e0 possibilidade de extrair dados do cache do processador que se acumulam durante a opera\u00e7\u00e3o de sistemas virtuais protegidos. O m\u00e9todo Prime+Probe pode ser usado para analisar o conte\u00fado do cache, que envolve preencher o cache com um conjunto de valores de refer\u00eancia e determinar altera\u00e7\u00f5es medindo o tempo de acesso a esses valores ao serem preenchidos novamente. Nota-se que m\u00e9todos previamente sugeridos para proteger contra ataques do tipo Spectre s\u00e3o adequados para bloquear esse ataque.
\n
Fonte: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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