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CVE Record

CVE-2025-38508: x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation

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 ]

HighCVSS 7.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux timing error can make long-running AMD SEV-SNP virtual machines drift from the hypervisor clock. Timers may appear to fire early, potentially disrupting workloads or availability. The supplied assessment rates it CVSS 7.3, primarily because availability impact may be high.

Executive priority

Treat this as a high-priority reliability issue where SEV-SNP protects important, long-running workloads. It is less urgent for environments that do not use SEV-SNP Secure TSC. Schedule vendor-approved updates promptly, while validating exposure before broad emergency action.

Technical view

Secure TSC timekeeping uses the nominal P0 frequency reported by GUEST_TSC_FREQ, although the actual mean frequency may differ by about 0.2%. Accumulated skew affects hrtimer behavior in SEV-SNP guests. The kernel fix calculates frequency using firmware TSC_FACTOR and maps the secrets page safely during early initialization.

Likely exposure

Exposure appears limited to Linux systems using Secure TSC in AMD SEV-SNP virtual machines. The supplied version data identifies 6.14, 6.15.7, and 6.16 as affected, but also contains an ambiguous “0” entry. Confirm exact distribution-specific ranges and backports with the vendor.

Exploitation context

The CVSS vector describes local attack proximity without required privileges or user interaction. However, the source bundle provides no exploit method or evidence of active exploitation, and the CVE is not listed as KEV. The documented failure is accumulated clock skew and inaccurate guest timer behavior.

Researcher notes

The correction consumes TSC_FACTOR from the SEV firmware secrets page to derive mean TSC frequency. Early initialization requires early_ioremap_encrypted because ioremap_encrypted depends on unavailable kmalloc and can panic. No CWE is supplied, and the provided version metadata is insufficiently clear for definitive range mapping.

Mitigation direction

  • Apply vendor-supported kernel updates containing the referenced stable fixes.
  • Prioritize long-running SEV-SNP guests using Secure TSC.
  • Check distribution advisories for exact affected versions and backport status.
  • Monitor affected guests for clock drift and abnormal timer behavior until updated.

Validation and detection

  • Inventory Linux kernel versions across SEV-SNP hosts and guests.
  • Confirm whether Secure TSC is enabled in each potentially affected environment.
  • Verify the vendor kernel includes either referenced fix or an equivalent backport.
  • After updating, monitor clock alignment and timer behavior during extended VM uptime.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2025-38508 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.3 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.3CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H2.54.7Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.3High
CVSS 3.1 vector shape for CVE-2025-38508Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux73bbf3b0fbba9aa27fef07a1fbd837661a863f03, 73bbf3b0fbba9aa27fef07a1fbd837661a863f03unaffected
LinuxLinux6.14, 0, 6.15.7, 6.16affected
Weakness

CWE details

No CWE listed

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