CVE-2025-38169: arm64/fpsimd: Avoid clobbering kernel FPSIMD state with SMSTOP

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: 2025-07-03 · updated 2026-10-15

Description

In the Linux kernel, the following vulnerability has been resolved: arm64/fpsimd: Avoid clobbering kernel FPSIMD state with SMSTOP On system with SME, a thread's kernel FPSIMD state may be erroneously clobbered during a context switch immediately after that state is restored. Systems without SME are unaffected. If the CPU happens to be in streaming SVE mode before a context switch to a thread with kernel FPSIMD state, fpsimd_thread_switch() will restore the kernel FPSIMD state using fpsimd_load_kernel_state() while the CPU is still in streaming SVE mode. When fpsimd_thread_switch() subsequently calls fpsimd_flush_cpu_state(), this will execute an SMSTOP, causing an exit from streaming SVE mode. The exit from streaming SVE mode will cause the hardware to reset a number of FPSIMD/SVE/SME registers, clobbering the FPSIMD state. Fix this by calling fpsimd_flush_cpu_state() before restoring the kernel FPSIMD state.

Affected products

Linux kernel: from 6.8.12 before 6.9; from 6.9.3 before 6.12.34; from 6.13 before 6.15.3 — fixed in 6.12.34, 6.15.3, 6.9

How to fix

Upgrade to a fixed version: Linux kernel 6.12.34, 6.15.3, 6.9. Check the vendor advisory for mitigations.

References

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