In the Linux kernel, the following vulnerability has been resolved:
x86/fpu: Fix NULL dereference in avx512_status()
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.
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 ]
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | 6.16 | 6.16.2 |
| linux / linux_kernel | 6.17-rc1 | 6.17-rc1.x |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
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