CVE-2025-38689
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-09-04

Last updated on: 2025-11-24

Assigner: kernel.org

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 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 ]
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Meta Information
Published
2025-09-04
Last Modified
2025-11-24
Generated
2026-05-07
AI Q&A
2025-09-04
EPSS Evaluated
2026-05-05
NVD
CVE-2025-38689
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
linux linux_kernel 6.17
linux linux_kernel From 5.15.160 (inc) to 5.16 (inc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-476 The product dereferences a pointer that it expects to be valid but is NULL.
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AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability is a NULL pointer dereference in the Linux kernel's x86/fpu code, specifically in the avx512_status() function. When CONFIG_X86_DEBUG_FPU is enabled, reading /proc/[kthread]/arch_status causes a warning and a NULL pointer dereference because the AVX-512 timestamp code uses x86_task_fpu() without checking if it returns NULL. Kernel threads (PF_KTHREAD) cause x86_task_fpu() to return NULL under this configuration, leading to the issue. The fix involved stopping the output of AVX-512 elapsed time for kernel threads, as the data was invalid for them.


How can this vulnerability impact me? :

This vulnerability can cause a kernel warning and a NULL pointer dereference when accessing certain kernel thread status files, potentially leading to kernel instability or crashes. It affects systems with CONFIG_X86_DEBUG_FPU enabled and could disrupt normal kernel operations involving kernel threads and their floating point unit (FPU) state handling.


What immediate steps should I take to mitigate this vulnerability?

The vulnerability is resolved by updating the Linux kernel to a version where the fix is applied. The fix involves stopping the output of AVX-512_elapsed_ms for kernel threads to avoid NULL pointer dereference. Therefore, the immediate mitigation step is to apply the kernel update that includes this fix.


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