{"id":100636,"date":"2021-06-30T22:23:10","date_gmt":"2021-06-30T20:23:10","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimost-v-speczifichnom-dlya-cpu-amd-kode-kvm-pozvolyayushhaya-vypolnit-kod-vne-gostevoj-sistemy"},"modified":"2021-06-30T22:23:10","modified_gmt":"2021-06-30T20:23:10","slug":"uyazvimost-v-speczifichnom-dlya-cpu-amd-kode-kvm-pozvolyayushhaya-vypolnit-kod-vne-gostevoj-sistemy","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/uyazvimost-v-speczifichnom-dlya-cpu-amd-kode-kvm-pozvolyayushhaya-vypolnit-kod-vne-gostevoj-sistemy","title":{"rendered":"Vulnerability in AMD CPU-specific KVM code allows code execution outside the guest system","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Researchers from the Google Project Zero team have identified a vulnerability (CVE-2021-29657) in the KVM hypervisor included in the Linux kernel, which allows for bypassing the isolation of the guest system and executing code on the host environment. The issue is present in the code used on systems with AMD processors (kvm-amd.ko module) and does not appear for Intel processors. <\/p>\n

Researchers have developed a working prototype of an exploit that allows launching a root shell in the host environment from a guest environment on a system with an AMD Epyc 7351P processor and Linux kernel 5.10. This marks the first vulnerability of the 'guest-to-host' class in the hypervisor itself. KVM<\/a>, unrelated to errors in user space components like QEMU. The fix was merged into the kernel at the end of March. The problem manifests starting with Linux kernel 5.10-rc1 and ending with v5.12-rc6, thus affecting only kernels 5.10 and 5.11 (most stable branches of distributions are not affected by this issue). <\/p>\n

The problem exists in the nested_svm_vmrun mechanism, implemented using the AMD SVM (Secure Virtual Machine) extension, which allows for nested execution of guest systems. For this functionality to be implemented correctly, the hypervisor must intercept all SVM instructions executed in the guest systems, emulate their behavior, and synchronize the state with the hardware, which is a quite complex task. Upon analyzing the KVM implementation, researchers found a logical error that allows affecting the contents of the host's MSR (Model-Specific Register) registers from the guest system, which can be exploited to execute code at the host level. <\/p>\n

Specifically, executing the VMRUN operation from the Level 2 guest system (L2, launched from another guest system) leads to a second call to nested_svm_vmrun and corruption of the structure svm->nested.hsave, onto which data from the L2 guest system's vmcb is applied. As a result, a situation arises where, at the L2 guest system level, memory can be freed in the svm->nested.msrpm structure, which holds the MSR bit, despite it still being in use, thus gaining access to the host environment's MSR.
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Source: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0418\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u0438 \u0438\u0437 \u043a\u043e\u043c\u0430\u043d\u0434\u044b Google Project Zero \u0432\u044b\u044f\u0432\u0438\u043b\u0438 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2021-29657) \u0432 \u043f\u043e\u0441\u0442\u0430\u0432\u043b\u044f\u0435\u043c\u043e\u043c \u0432 \u0441\u043e\u0441\u0442\u0430\u0432\u0435 \u044f\u0434\u0440\u0430 Linux \u0433\u0438\u043f\u0435\u0440\u0432\u0438\u0437\u043e\u0440\u0435 KVM, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0443\u044e \u043e\u0431\u043e\u0439\u0442\u0438 \u0438\u0437\u043e\u043b\u044f\u0446\u0438\u044e \u0433\u043e\u0441\u0442\u0435\u0432\u043e\u0439 \u0441\u0438\u0441\u0442\u0435\u043c\u044b \u0438 \u0432\u044b\u043f\u043e\u043b\u043d\u0438\u0442\u044c \u0441\u0432\u043e\u0439 \u043a\u043e\u0434 \u043d\u0430 \u0441\u0442\u043e\u0440\u043e\u043d\u0435 \u0445\u043e\u0441\u0442-\u043e\u043a\u0440\u0443\u0436\u0435\u043d\u0438\u044f. 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