{"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\/en\/blog\/news\/uyazvimost-v-zagruzchike-mikrokoda-v-cpu-amd-pozvolyayushhaya-obojti-izolyacziyu-sev-snp","title":{"rendered":"A vulnerability in the microcode loader in AMD CPUs allows bypassing SEV-SNP isolation.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Security researchers from Google have published information about a vulnerability (CVE-2024-56161) in AMD processors that affects the microcode loader and allows bypassing the digital signature verification mechanism during microcode updates. Loading modified microcode can compromise the AMD SEV (Secure Encrypted Virtualization) mechanism used in virtualization systems to protect virtual machines from interference by the hypervisor or the host system administrator. <\/p>\n

The vulnerability arises from the use of an insecure hash function in the code performing digital signature verification after loading microcode into the CPU. To execute the attack, administrative privileges in the local system are required (the ability to execute code at ring0 level while not being in a virtual machine). <\/p>\n

During the attack, it is possible to infiltrate the operation of guest systems protected by AMD SEV (Secure Encrypted Virtualization) and SEV-SNP (Secure Nested Paging) extensions, which provide memory integrity guarantees. of virtual machines<\/a>, isolating CPU registers and ensuring secure handling of nested page tables. The AMD SEV mechanism was created so that data center staff and cloud providers could not alter or analyze the contents of memory in protected guest systems or distort computations. <\/p>\n

Researchers have prepared a prototype exploit that allows arbitrary microcode to be loaded into the CPU without a valid digital signature. To demonstrate the danger of the vulnerability, a microcode update is proposed that changes the logic of the RDRAND instruction, which is used as one of the sources of entropy in pseudorandom number generators employed in key generation processes, during cryptographic operations, and for generating random identifiers. <\/p>\n

The change results in the RDRAND instruction returning only the number 4 instead of a random sequence. To prevent real attacks on confidential computing systems, the modified microcode resets the CF (carry flag), marking the issued value as erroneous. Additional details and tools for generating the modified microcode are expected to be published on March 5, allowing users time to install the fix on their systems. A successful attack example has been demonstrated for servers<\/a> AMD EPYC 7B13 (Milan) and AMD Ryzen 9 7940HS (Phoenix) processors. <\/p>\n

AMD's report indicates that the vulnerability appears in AMD processors based on the first to fourth generations of the Zen microarchitecture. A microcode update addressing the vulnerability was released on December 13, 2024, for AMD EPYC series 7001, 7002, and 7003 (Naples, Rome, Milan, and Milan-X) processors, and on December 16 for AMD EPYC series 9004 (Genoa, Genoa-X, and Bergamo\/Siena) processors. An additional update of the AMD SEV firmware (provided with BIOS updates from hardware manufacturers) is required to eliminate the vulnerability on systems using SEV-SNP attestation. <\/p>\n

There is also reporting of another vulnerability in AMD processors that allows side-channel attacks to extract information from computations in guest systems protected by the AMD SEV mechanism. This issue affects the first to fourth generations of AMD EPYC processors and is related to the ability to extract data residing in the processor cache during the operation of protected guest systems. The Prime+Probe method can be used to analyze the cache contents, which involves filling the cache with a reference set of values and determining changes by measuring access time when refilling. It is noted that methods previously proposed for protecting against Spectre-class attacks are suitable for blocking this attack.
\n
Source: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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