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Date:   Fri, 5 Feb 2021 14:59:27 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Arnd Bergmann <arnd@arndb.de>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
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        Randy Dunlap <rdunlap@infradead.org>,
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        Weijiang Yang <weijiang.yang@intel.com>,
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        Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [PATCH v19 06/25] x86/cet: Add control-protection fault handler
Message-ID: <20210205135927.GH17488@zn.tnic>
References: <20210203225547.32221-1-yu-cheng.yu@intel.com>
 <20210203225547.32221-7-yu-cheng.yu@intel.com>
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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?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette