CVE-2021-29657

A flaw was found in the Linux kernel. A KVM guest on AMD can launch a nested guest without the Intercept VMRUN control bit by exploiting a TOCTOU vulnerability in nested_svm_vmrun. A malicious guest could use this flaw to gain unrestricted access to host MSRs, possibly leading to guest-to-host escape scenario.

Mitigation

This vulnerability can be mitigated by disabling the nested virtualization feature:

# modprobe -r kvm_amd  
# modprobe kvm_amd nested=0