Bug 2376067 (CVE-2025-38169)

Summary: CVE-2025-38169 kernel: Linux kernel: Data corruption due to FPSIMD state clobbering during context switch
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel. A local attacker could exploit a vulnerability in the `arm64/fpsimd` component on systems with Scalable Matrix Extension (SME) when the CPU is in streaming SVE mode. This flaw causes the kernel's Floating-Point and SIMD (FPSIMD) state to be erroneously overwritten during a context switch, leading to potential data corruption and system instability.
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Description OSIDB Bzimport 2025-07-03 09:03:18 UTC 
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.
Comment 1 Avinash Hanwate 2025-07-03 17:17:27 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025070342-CVE-2025-38169-11b6@gregkh/T