ghsa-p2wm-x2jh-86vj
Vulnerability from github
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": [],
"aliases": [
"CVE-2025-38508"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-08-16T11:15:43Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/sev: Use TSC_FACTOR for Secure TSC frequency calculation\n\nWhen using Secure TSC, the GUEST_TSC_FREQ MSR reports a frequency based on\nthe nominal P0 frequency, which deviates slightly (typically ~0.2%) from\nthe actual mean TSC frequency due to clocking parameters.\n\nOver extended VM uptime, this discrepancy accumulates, causing clock skew\nbetween the hypervisor and a SEV-SNP VM, leading to early timer interrupts as\nperceived by the guest.\n\nThe guest kernel relies on the reported nominal frequency for TSC-based\ntimekeeping, while the actual frequency set during SNP_LAUNCH_START may\ndiffer. This mismatch results in inaccurate time calculations, causing the\nguest to perceive hrtimers as firing earlier than expected.\n\nUtilize the TSC_FACTOR from the SEV firmware\u0027s secrets page (see \"Secrets\nPage Format\" in the SNP Firmware ABI Specification) to calculate the mean\nTSC frequency, ensuring accurate timekeeping and mitigating clock skew in\nSEV-SNP VMs.\n\nUse early_ioremap_encrypted() to map the secrets page as\nioremap_encrypted() uses kmalloc() which is not available during early TSC\ninitialization and causes a panic.\n\n [ bp: Drop the silly dummy var:\n https://lore.kernel.org/r/20250630192726.GBaGLlHl84xIopx4Pt@fat_crate.local ]",
"id": "GHSA-p2wm-x2jh-86vj",
"modified": "2025-08-16T12:30:32Z",
"published": "2025-08-16T12:30:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38508"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/52e1a03e6cf61ae165f59f41c44394a653a0a788"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d0195c42e65805938c9eb507657e7cdf8e1e9522"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
| Author | Source | Type | Date |
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