CVE-2025-38689

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

x86/fpu: Fix NULL dereference in avx512_status()

Problem

-------

With CONFIG_X86_DEBUG_FPU enabled, reading /proc/[kthread]/arch_status

causes a warning and a NULL pointer dereference.

This is because the AVX-512 timestamp code uses x86_task_fpu() but

doesn't check it for NULL. CONFIG_X86_DEBUG_FPU addles that function

for kernel threads (PF_KTHREAD specifically), making it return NULL.

The point of the warning was to ensure that kernel threads only access

task->fpu after going through kernel_fpu_begin()/_end(). Note: all

kernel tasks exposed in /proc have a valid task->fpu.

Solution

--------

One option is to silence the warning and check for NULL from

x86_task_fpu(). However, that warning is fairly fresh and seems like a

defense against misuse of the FPU state in kernel threads.

Instead, stop outputting AVX-512_elapsed_ms for kernel threads

altogether. The data was garbage anyway because avx512_timestamp is

only

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References