linux-kernel - Re: [PATCH v17 06/26] x86/cet: Add control-protection fault handler

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Date:   Tue, 19 Jan 2021 11:36:31 -0800
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH v17 06/26] x86/cet: Add control-protection fault handler

On 1/19/2021 4:04 AM, Borislav Petkov wrote:
> On Tue, Dec 29, 2020 at 01:30:33PM -0800, Yu-cheng Yu wrote:
[...]
>> +DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
>> +{
>> +	struct task_struct *tsk;
>> +
>> +	if (!user_mode(regs)) {
>> +		if (notify_die(DIE_TRAP, "control protection fault", regs,
>> +			       error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP)
>> +			return;
>> +		die("Upexpected/unsupported kernel control protection fault", regs, error_code);
> 
> Isn't the machine supposed to panic() here and do no further progress?

Ok, make it panic().

>> +	}
>> +
>> +	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) &&
>> +	    printk_ratelimit()) {
> 
> WARNING: Prefer printk_ratelimited or pr_<level>_ratelimited to printk_ratelimit
> #136: FILE: arch/x86/kernel/traps.c:645:
> +	    printk_ratelimit()) {
> 
> Still not using checkpatch?

Most places in arch/x86 still use printk_ratelimit().  I should have 
trusted checkpatch.  I will fix it.

>> +		unsigned int max_err;
>> +		unsigned long ssp;
>> +
>> +		max_err = ARRAY_SIZE(control_protection_err) - 1;
>> +		if ((error_code < 0) || (error_code > max_err))
>> +			error_code = 0;
>> +
>> +		rdmsrl(MSR_IA32_PL3_SSP, ssp);
>> +		pr_info("%s[%d] control protection ip:%lx sp:%lx ssp:%lx error:%lx(%s)",
> 
> If anything, all this stuff should be pr_emerg().

I will fix it.

--
Yu-cheng