# Re: \[PATCH v19 06/25\] x86/cet: Add control-protection fault handler

- From: Yu, Yu-cheng \<hidden\>
- Date: 2021-02-05 18:05:06 
- List: linux-doc
- Page: https://ratatoskr.run/linux-doc/2021/02/6260116
- Thread: https://ratatoskr.run/linux-doc/2021/02/6257763/t.md

```text
On 2/5/2021 5:59 AM, Borislav Petkov wrote:
> On Wed, Feb 03, 2021 at 02:55:28PM -0800, Yu-cheng Yu wrote:
>> +DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
>> +{
>> +	static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
>> +				      DEFAULT_RATELIMIT_BURST);
>> +	struct task_struct *tsk;
>> +
>> +	if (!user_mode(regs)) {
>> +		pr_emerg("PANIC: unexpected kernel control protection fault\n");
>> +		die("kernel control protection fault", regs, error_code);
>> +		panic("Machine halted.");
>> +	}
>> +
>> +	cond_local_irq_enable(regs);
>> +
>> +	if (!boot_cpu_has(X86_FEATURE_CET))
>> +		WARN_ONCE(1, "Control protection fault with CET support disabled\n");
>> +
>> +	tsk = current;
>> +	tsk->thread.error_code = error_code;
>> +	tsk->thread.trap_nr = X86_TRAP_CP;
>> +
>> +	if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
>> +	    __ratelimit(&rs)) {
>
> I can't find it written down anywhere why the ratelimiting is needed at
> all?
>

The ratelimit here is only for #CP, and its rate is not counted together with other types of faults.  If a task gets here, it will exit.  The only condition the ratelimit will trigger is when multiple tasks hit #CP at once, which is unlikely.  Are you suggesting that we do not need the ratelimit here?

Thanks!

--
Yu-cheng
```