Re: [PATCH] kprobes: avoid crash when rmmod/insmod modules after ftrace_disabled

[yebin <yebin@huaweicloud.com>]

On 2025/12/3 0:43, Steven Rostedt wrote:
> On Fri, 28 Nov 2025 10:27:42 +0800
> yebin <yebin@huaweicloud.com> wrote:
>
>>>> right before this BUG, don't you?
>>>> If you reported with that line, it's more easier to understand.
>>>>
>> Yes, there is indeed a warning generated. I might not have expressed it
>> clearly enough. The issue below is related to the problem that occurs
>> when the second module is unloaded. When the first module was unloaded,
>> some nodes were left in the hash list, causing a use-after-free (UAF)
>> issue when traversing the hash list.
>> Therefore, this patch aims to resolve the UAF problem caused by residual
>> nodes in the hash list after unloading a module while ftrace is disabled.
>
> ftrace_disabled is equivalent to BUG(). But it doesn't crash the system
> immediately, but requires a reboot ASAP.
>
> I'm not interested in fixing residual bugs that happen because of a
> ftrace_disabled was triggered. The ftrace_disabled triggering is the cause
> of this. It should *never* happen. If it does, it needs to be fixed.
>
> Let's focus our attention on fixing the cause of ftrace_disabled. Anything
> else is just waste of effort.
>
> Do you have the output of the first warning when ftrace_disabled was
> triggered?

The reason for ftrace_disable is a conflict between a livepatch and a 
module. This issue must be resolved. However, since this problem occurs 
in the current network environment, it does not affect the normal 
operation of services, so customers may not necessarily be willing to 
restart their systems to fix it. The only thing that can be done is to 
implement proper exception protection to ensure the system can continue 
to function until the customer is willing to upgrade and restart.

  WARNING: CPU: 0 PID: 2394 at kernel/trace/ftrace.c:2603 
ftrace_modify_all_code+0x81/0x140
  CPU: 0 PID: 2394 Comm: insmod Tainted: P           OE K
  RIP: 0010:ftrace_modify_all_code+0x81/0x140
  Call Trace:
   arch_ftrace_update_code+0xc/0x20
   ftrace_run_update_code+0x13/0x70
   ftrace_startup+0xc0/0x190
   register_ftrace_function+0x44/0x60
   arm_kprobe+0xc7/0x120
   register_kprobe+0x5f0/0x6a0
   kxxx_emerge_init+0x89/0xe0 [kxxx]
   kxxx_region_init+0x16d/0x330 [kxxx]
   kxxx_init+0xe3/0x1000 [kxxx]
   do_one_initcall+0x46/0x1c8
   do_init_module+0x5b/0x1fb
   load_module+0x15a7/0x1e20
   __do_sys_finit_module+0xe9/0x110
   do_syscall_64+0x5b/0x1b0
   entry_SYSCALL_64_after_hwframe+0x65/0xca
>
> -- Steve
>