CVE-2024-44948: x86/mtrr: Check if fixed MTRRs exist before saving them

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-09-04 · updated 2026-10-15

Description

In the Linux kernel, the following vulnerability has been resolved: x86/mtrr: Check if fixed MTRRs exist before saving them MTRRs have an obsolete fixed variant for fine grained caching control of the 640K-1MB region that uses separate MSRs. This fixed variant has a separate capability bit in the MTRR capability MSR. So far all x86 CPUs which support MTRR have this separate bit set, so it went unnoticed that mtrr_save_state() does not check the capability bit before accessing the fixed MTRR MSRs. Though on a CPU that does not support the fixed MTRR capability this results in a #GP. The #GP itself is harmless because the RDMSR fault is handled gracefully, but results in a WARN_ON(). Add the missing capability check to prevent this.

Affected products

Linux kernel: from 2.6.22 before 4.19.320; from 4.20 before 5.4.282; from 5.5 before 5.10.224; from 5.11 before 5.15.165; from 5.16 before 6.1.105; from 6.2 before 6.6.46 — fixed in 4.19.320, 5.10.224, 5.15.165, 5.4.282, 6.1.105, 6.10.5

How to fix

Upgrade to a fixed version: Linux kernel 4.19.320, 5.10.224, 5.15.165, 5.4.282. Check the vendor advisory for mitigations.

References

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