Fushuai Wang 2ca887e810 x86/fpu: Fix NULL dereference in avx512_status() ... commit 31cd31c9e1 upstream. 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 ] Fixes: 22aafe3bcb ("x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks") Co-developed-by: Sohil Mehta <sohil.mehta@intel.com> Signed-off-by: Sohil Mehta <sohil.mehta@intel.com> Signed-off-by: Fushuai Wang <wangfushuai@baidu.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20250811185044.2227268-1-sohil.mehta%40intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2025-08-20 18:41:35 +02:00
..
bugs.c
context.h	x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu()	2025-04-14 08:18:29 +02:00
core.c	Core x86 updates for v6.16:	2025-05-26 16:04:17 -07:00
init.c	Core x86 updates for v6.16:	2025-05-26 16:04:17 -07:00
internal.h
legacy.h
Makefile
regset.c	x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu()	2025-04-14 08:18:29 +02:00
signal.c	x86/fpu: Refactor xfeature bitmask update code for sigframe XSAVE	2025-04-16 10:01:00 +02:00
xstate.c	x86/fpu: Fix NULL dereference in avx512_status()	2025-08-20 18:41:35 +02:00
xstate.h	Merge branch 'x86/msr' into x86/core, to resolve conflicts	2025-05-13 10:42:06 +02:00