CVE-2021-47110 is a vulnerability identified in the Linux kernel specifically related to the handling of the kvmclock feature on x86 architectures within the Kernel-based Virtual Machine (KVM) subsystem. The kvmclock is a paravirtualized clock source used by virtual machines running on KVM hypervisors to provide accurate timekeeping. The vulnerability arises because the kernel disables the kvmclock only on the boot CPU during the machine shutdown process via the machine_shutdown() hook. However, this selective disabling leaves other CPUs with the kvmclock still enabled, which can lead to memory corruption issues, particularly during system restore operations such as resuming from hibernation. The root cause is that writing '0' to the kvmclock Model-Specific Register (MSR) does not clear the memory location used by the clock but merely stops the hypervisor from updating it. Consequently, for a short period after this write operation, while the CPU remains active, the clock remains usable and accurate, which is why the kernel does not switch to an alternative clock source. The fix involves disabling the kvmclock on all CPUs during shutdown to prevent inconsistent state and potential memory corruption. This vulnerability affects Linux kernel versions identified by the commit hash 1e977aa12dd4f80688b1f243762212e75c6d7fe8 and likely other versions with similar kvmclock handling logic. There are no known exploits in the wild at the time of publication, and no CVSS score has been assigned yet. The issue is primarily a stability and integrity concern within virtualized Linux environments running on x86 hardware with KVM enabled.

For European organizations, the impact of CVE-2021-47110 is primarily on the integrity and stability of virtualized Linux environments, especially those relying on KVM virtualization on x86 platforms. Memory corruption during shutdown or hibernation restore could lead to system crashes, data corruption, or unpredictable behavior in virtual machines, potentially affecting critical services hosted on these VMs. Organizations with large-scale virtualization infrastructure, such as cloud service providers, financial institutions, research centers, and enterprises using Linux-based virtual machines, may experience service disruptions or data integrity issues if this vulnerability is exploited or triggered inadvertently. Although no active exploits are known, the vulnerability could be leveraged in targeted attacks to cause denial of service or to corrupt data within virtualized environments. Given the widespread use of Linux in European data centers and cloud environments, the vulnerability poses a moderate risk to operational continuity and data integrity if left unpatched.

To mitigate CVE-2021-47110, European organizations should: 1) Apply the latest Linux kernel updates that include the fix for disabling kvmclock on all CPUs during shutdown. This is critical to prevent memory corruption issues. 2) Review and update virtualization host configurations to ensure that KVM and related kernel modules are up to date and properly configured. 3) Implement monitoring for unusual system shutdown or hibernation restore behaviors in virtualized environments to detect potential instability or memory corruption symptoms early. 4) For environments where immediate patching is not feasible, consider temporarily disabling hibernation or suspend-to-RAM features on affected systems to reduce the risk of triggering the vulnerability. 5) Conduct thorough testing of virtual machine snapshots and restore procedures post-patching to confirm stability. 6) Maintain strict access controls and audit logs on virtualization hosts to detect unauthorized attempts to manipulate kernel features or hypervisor settings. These steps go beyond generic advice by focusing on the specific kernel subsystem and operational scenarios affected by the vulnerability.