CVE-2021-29657

Name of the Vulnerable Software and Affected Versions Linux kernel versions prior to 5.11.12

Description The issue is related to a use-after-free vulnerability in the arch/x86/kvm/svm/nested.c component of the Linux kernel, specifically affecting AMD KVM guests. This vulnerability can be exploited to bypass access control on host OS MSRs when there are nested guests, due to a TOCTOU race condition associated with a VMCB12 double fetch in nested svm vmrun. The vulnerability allows an attacker to execute code outside of the guest system, potentially leading to privilege escalation.

Recommendations For Linux kernel versions prior to 5.11.12, update to version 5.11.12 or later to resolve the issue. As a temporary workaround, consider disabling the nested guest feature in AMD KVM until a patch is available. Restrict access to the vulnerable arch/x86/kvm/svm/nested.c component to minimize the risk of exploitation. Avoid using the nested svm vmrun function until the issue is resolved.