CVE-2025-40042: In the Linux kernel, the following vulnerability has been resolved:  tracing: Fix race condition in kprobe initialization causing NULL pointer dereference  There is a critical race condition in kprobe initialization that can lead to NULL pointer dereference and kernel crash.  [1135630.084782] Unable to handle kernel paging request at virtual address 0000710a04630000 ... [1135630.260314] pstate: 404003c9 (nZcv DAIF +PAN -UAO) [1135630.269239] pc : kprobe_perf_func+0x30/0x260 [1135630.277643] lr : kprobe_dispatcher+0x44/0x60 [1135630.286041] sp : ffffaeff4977fa40 [1135630.293441] x29: ffffaeff4977fa40 x28: ffffaf015340e400 [1135630.302837] x27: 0000000000000000 x26: 0000000000000000 [1135630.312257] x25: ffffaf029ed108a8 x24: ffffaf015340e528 [1135630.321705] x23: ffffaeff4977fc50 x22: ffffaeff4977fc50 [1135630.331154] x21: 0000000000000000 x20: ffffaeff4977fc50 [1135630.340586] x19: ffffaf015340e400 x18: 0000000000000000 [1135630.349985] x17: 0000000000000000 x16: 0000000000000000 [1135630.359285] x15: 0000000000000000 x14: 0000000000000000 [1135630.368445] x13: 0000000000000000 x12: 0000000000000000 [1135630.377473] x11: 0000000000000000 x10: 0000000000000000 [1135630.386411] x9 : 0000000000000000 x8 : 0000000000000000 [1135630.395252] x7 : 0000000000000000 x6 : 0000000000000000 [1135630.403963] x5 : 0000000000000000 x4 : 0000000000000000 [1135630.412545] x3 : 0000710a04630000 x2 : 0000000000000006 [1135630.421021] x1 : ffffaeff4977fc50 x0 : 0000710a04630000 [1135630.429410] Call trace: [1135630.434828]  kprobe_perf_func+0x30/0x260 [1135630.441661]  kprobe_dispatcher+0x44/0x60 [1135630.448396]  aggr_pre_handler+0x70/0xc8 [1135630.454959]  kprobe_breakpoint_handler+0x140/0x1e0 [1135630.462435]  brk_handler+0xbc/0xd8 [1135630.468437]  do_debug_exception+0x84/0x138 [1135630.475074]  el1_dbg+0x18/0x8c [1135630.480582]  security_file_permission+0x0/0xd0 [1135630.487426]  vfs_write+0x70/0x1c0 [1135630.493059]  ksys_write+0x5c/0xc8 [1135630.498638]  __arm64_sys_write+0x24/0x30 [1135630.504821]  el0_svc_common+0x78/0x130 [1135630.510838]  el0_svc_handler+0x38/0x78 [1135630.516834]  el0_svc+0x8/0x1b0  kernel/trace/trace_kprobe.c: 1308 0xffff3df8995039ec <kprobe_perf_func+0x2c>:     ldr     x21, [x24,#120] include/linux/compiler.h: 294 0xffff3df8995039f0 <kprobe_perf_func+0x30>:     ldr     x1, [x21,x0]  kernel/trace/trace_kprobe.c 1308: head = this_cpu_ptr(call->perf_events); 1309: if (hlist_empty(head)) 1310:  return 0;  crash> struct trace_event_call -o struct trace_event_call {   ...   [120] struct hlist_head *perf_events;  //(call->perf_event)   ... }  crash> struct trace_event_call ffffaf015340e528 struct trace_event_call {   ...   perf_events = 0xffff0ad5fa89f088, //this value is correct, but x21 = 0   ... }  Race Condition Analysis:  The race occurs between kprobe activation and perf_events initialization:    CPU0                                    CPU1   ====                                    ====   perf_kprobe_init     perf_trace_event_init       tp_event->perf_events = list;(1)       tp_event->class->reg (2)← KPROBE ACTIVE                                           Debug exception triggers                                           ...                                           kprobe_dispatcher                                             kprobe_perf_func (tk->tp.flags & TP_FLAG_PROFILE)                                               head = this_cpu_ptr(call->perf_events)(3)                                               (perf_events is still NULL)  Problem: 1. CPU0 executes (1) assigning tp_event->perf_events = list 2. CPU0 executes (2) enabling kprobe functionality via class->reg() 3. CPU1 triggers and reaches kprobe_dispatcher 4. CPU1 checks TP_FLAG_PROFILE - condition passes (step 2 completed) 5. CPU1 calls kprobe_perf_func() and crashes at (3) because    call->perf_events is still NULL  CPU1 sees that kprobe functionality is enabled but does not see that perf_events has been assigned.  Add pairing read an ---truncated---