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

> Clock skew in SEV-SNP VMs causes early timer interrupts and potential kernel panics, requiring a patch to use TSC_FACTOR for accurate timekeeping.

- **Severity:** High 7.3 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Aug 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-38508, GHSA-p2wm-x2jh-86vj, UBUNTU-CVE-2025-38508

## What is CVE-2025-38508?

CVE-2025-38508 is a high-severity denial of service vulnerability in Linux kernel, published on 16 Aug 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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 ]

## Which versions are affected by CVE-2025-38508?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38508?

Apply the vendor's patch.

## Is CVE-2025-38508 being exploited?

There is no known exploitation of CVE-2025-38508 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38508 and fix it if it is affected.

What it is: CVE-2025-38508 is a high-severity denial of service vulnerability in Linux kernel, published on 16 Aug 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-38508 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-38508/ (Markdown: https://insights.sbomify.com/CVE-2025-38508/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38508
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38508
- OSV: https://osv.dev/vulnerability/CVE-2025-38508

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38508/
Summaries are generated and may contain mistakes; the official description above is the record.