{"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\/da\/blog\/news\/uyazvimost-v-zagruzchike-mikrokoda-v-cpu-amd-pozvolyayushhaya-obojti-izolyacziyu-sev-snp","title":{"rendered":"S\u00e5rbarhed i mikrokodebootloaderen i AMD CPU, der tillader omg\u00e5else af SEV-SNP isolering","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Sikkerhedsforskere fra Google har offentliggjort information om en s\u00e5rbarhed (CVE-2024-56161) i AMD-processorer, som ber\u00f8rer mikrocode-loaderen og g\u00f8r det muligt at omg\u00e5 mekanismen til digital signaturkontrol ved opdateringer af mikrocode. Indl\u00e6sning af modificeret mikrocode kan kompromittere mekanismen AMD SEV (Secure Encrypted Virtualization), der anvendes i virtualiseringssystemer til at beskytte virtuelle maskiner mod indgreb fra hypervisoren eller administratoren af v\u00e6rtsystemet. <\/p>\n

S\u00e5rbarheden skyldes brugen af en usikker hash-funktion i koden, der udf\u00f8rer kontrol af den digitale signatur efter indl\u00e6sning af mikrocode i CPU'en. For at udf\u00f8re et angreb er det n\u00f8dvendigt at have administratorrettigheder i det lokale system (muligheden for at udf\u00f8re kode p\u00e5 ring0-niveau, mens man ikke er i en virtuel maskine). <\/p>\n

Under et angreb kan man tr\u00e6nge ind i arbejdet med g\u00e6stesystemer, der er beskyttet ved hj\u00e6lp af AMD SEV (Secure Encrypted Virtualization) og SEV-SNP (Secure Nested Paging), som giver garantier for integriteten af hukommelsen. virtual machines<\/a>, der isolerer CPU-registere og sikrer sikker h\u00e5ndtering af indlejrede side-tabeller i hukommelsen. AMD SEV-mekanismen blev skabt for at sikre, at personale i datacentre og cloud-udbydere ikke kunne \u00e6ndre eller analysere indholdet af hukommelsen i beskyttede g\u00e6stesystemer samt forvr\u00e6nge beregninger. <\/p>\n

Forskere har udarbejdet en prototype af et exploit, der g\u00f8r det muligt at indl\u00e6se vilk\u00e5rlig mikrocode i CPU'en, som ikke er signeret med en digital signatur. For at demonstrere faren ved s\u00e5rbarheden er der foresl\u00e5et en opdatering af mikrocode, der \u00e6ndrer logikken i RDRAND-instruktionen, anvendt som en af kilderne til entropi i pseudorandom number generators, der bruges i n\u00f8glegenerering, ved udf\u00f8relse af kryptografiske operationer og til generation af tilf\u00e6ldige identifikatorer. <\/p>\n

\u00c6ndringen medf\u00f8rer, at RDRAND-instruktionen kun returnerer tallet 4 i stedet for en tilf\u00e6ldig sekvens. For at forhindre reelle angreb p\u00e5 systemer med konfidentiale beregninger nulstiller den \u00e6ndrede mikrokode CF-flaget (carry flag), hvilket betyder, at den udsendte v\u00e6rdi markeres som fejlbeh\u00e6ftet. Yderligere detaljer og v\u00e6rkt\u00f8jer til at generere den \u00e6ndrede mikrokode planl\u00e6gges at blive offentliggjort den 5. marts for at give brugerne tid til at installere opdateringen p\u00e5 deres systemer. Et vellykket eksempel p\u00e5 et angreb er demonstreret for servere<\/a> med AMD EPYC 7B13 (Milan) og AMD Ryzen 9 7940HS (Phoenix). <\/p>\n

I AMD's rapport angives det, at s\u00e5rbarheden forekommer i AMD-processorer baseret p\u00e5 1-4 generationer af Zen-mikroarkitekturen. Mikrokodeopdateringen, der l\u00f8ser s\u00e5rbarheden, blev udgivet den 13. december 2024 for AMD EPYC 7001, 7002 og 7003 (Naples, Rome, Milan og Milan-X) processorer, og den 16. december for AMD EPYC 9004 (Genoa, Genoa-X og Bergamo\/Siena) processorer. For at l\u00f8se s\u00e5rbarheden p\u00e5 systemer, der anvender SEV-SNP attestation, kr\u00e6ves der desuden en opdatering af AMD SEV-firmware (som leveres sammen med BIOS-opdateringer fra hardwareproducenterne). <\/p>\n

Der rapporteres desuden om endnu en s\u00e5rbarhed i AMD-processorer, som muligg\u00f8r angreb via sidekanaler for at udtr\u00e6kke information om beregninger i g\u00e6stesystemer, der er beskyttet ved hj\u00e6lp af AMD SEV-mekanismen. Problemet ber\u00f8rer 1-4 generationer af AMD EPYC-processorer og er relateret til muligheden for at udtr\u00e6kke data fra processorcache, der samler sig under drift af beskyttede g\u00e6stesystemer. Metoden Prime+Probe kan anvendes til at analysere cacheindholdet, hvilket indeb\u00e6rer, at cachen fyldes med et reference s\u00e6t v\u00e6rdier, og \u00e6ndringerne bestemmes ved at m\u00e5le adgangstids\u00e6ndringer ved gentagen fyldning. Der bem\u00e6rkes, at metoder, der tidligere blev foresl\u00e5et til beskyttelse mod Spectre-klasse angreb, er egnede til at blokere dette angreb.
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Kilde: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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