CVE Catalog

CVE-2025-38689

MediumCVSS 5.5
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.14%

3th percentile - higher than 3% of all known CVEs

Summary

In the Linux kernel with CONFIG_X86_DEBUG_FPU, reading /proc/[kthread]/arch_status causes a warning and NULL pointer dereference because AVX-512 timestamp code uses x86_task_fpu() without NULL check for kernel threads. The fix stops outputting AVX-512_elapsed_ms for kernel threads.

Risk Assessment

May cause kernel warnings and NULL dereference when reading arch_status for kernel threads, potentially leading to denial of service on systems with FPU debugging enabled.

Recommendation

Update the Linux kernel to a version containing the fix that removes AVX-512_elapsed_ms output for kernel threads in avx512_status().

Other vulnerabilities in Linux kernel

See all
Original NVD description (English source)

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 updated for user threads, not kernel threads. If anyone ever wants to track kernel thread AVX-512 use, they can come back later and do it properly, separate from this bug fix. [ dhansen: mostly rewrite changelog ]

Vulnerability data from NVD (NIST) · CISA KEV · EPSS