Linux Kernel Secure TSC Frequency Calculation Vulnerability in SEV-SNP VMs

A vulnerability in the Linux kernel's handling of Secure TSC (Time Stamp Counter) frequency calculation for SEV-SNP (Secure Encrypted Virtualization - Secure Nested Paging) virtual machines has been addressed. The issue arose because the GUEST_TSC_FREQ MSR (Model Specific Register) reported a frequency based on the nominal P0 frequency, which typically deviated by about 0.2% from the actual mean TSC frequency due to clocking parameters. Over prolonged VM uptime, this discrepancy accumulated, causing a clock skew between the hypervisor and the SEV-SNP VM. As a result, the guest perceived timer interrupts as firing earlier than expected. This vulnerability affected several versions of the Linux kernel.

Impact

The vulnerability could lead to inaccurate timekeeping in SEV-SNP VMs, causing the guest operating system to misinterpret the timing of scheduled events, such as hrtimer interrupts, which could disrupt the normal operation of time-sensitive applications.

Remediation

The vulnerability has been fixed in the Linux kernel. Users should upgrade to the latest version available in the Linux kernel stable tree.