Description

In the Linux kernel, the following vulnerability has been resolved: x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation When using Secure TSC, the GUEST_TSC_FREQ MSR reports a frequency based on the nominal P0 frequency, which deviates slightly (typically ~0.2%) from the actual mean TSC frequency due to clocking parameters. Over extended VM uptime, this discrepancy accumulates, causing clock skew between the hypervisor and a SEV-SNP VM, leading to early timer interrupts as perceived by the guest. The guest kernel relies on the reported nominal frequency for TSC-based timekeeping, while the actual frequency set during SNP_LAUNCH_START may differ. This mismatch results in inaccurate time calculations, causing the guest to perceive hrtimers as firing earlier than expected. Utilize the TSC_FACTOR from the SEV firmware's secrets page (see "Secrets Page Format" in the SNP Firmware ABI Specification) to calculate the mean TSC frequency, ensuring accurate timekeeping and mitigating clock skew in SEV-SNP VMs. Use early_ioremap_encrypted() to map the secrets page as ioremap_encrypted() uses kmalloc() which is not available during early TSC initialization and causes a panic. [ bp: Drop the silly dummy var: https://lore.kernel.org/r/20250630192726.GBaGLlHl84xIopx4Pt@fat_crate.local ]

Affected Products 5

References 2

• git.kernel.org https://git.kernel.org/stable/c/52e1a03e6cf61ae165f59f41c44394a653a0a788
  Patch
• git.kernel.org https://git.kernel.org/stable/c/d0195c42e65805938c9eb507657e7cdf8e1e9522
  Patch

Remediation

• git.kernel.org https://git.kernel.org/stable/c/52e1a03e6cf61ae165f59f41c44394a653a0a788
  Patch
• git.kernel.org https://git.kernel.org/stable/c/d0195c42e65805938c9eb507657e7cdf8e1e9522
  Patch