linux-kernel - Re: [patch V3 04/23] kprobes: Prevent probes in .noinstr.text section

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Message-ID: <87mu87oy7n.fsf@nanos.tec.linutronix.de>
Date:   Mon, 23 Mar 2020 17:03:24 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Paul McKenney <paulmck@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Joel Fernandes \(Google\)" <joel@...lfernandes.org>,
        "Steven Rostedt \(VMware\)" <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [patch V3 04/23] kprobes: Prevent probes in .noinstr.text section

Masami,

Masami Hiramatsu <mhiramat@...nel.org> writes:
> On Fri, 20 Mar 2020 19:00:00 +0100
> Thomas Gleixner <tglx@...utronix.de> wrote:
>
>> Instrumentation is forbidden in the .noinstr.text section. Make kprobes
>> respect this.
>> 
>> This lacks support for .noinstr.text sections in modules, which is required
>> to handle VMX and SVM.
>> 
>
> Would you have any plan to list or mark the noinstr symbols on
> some debugfs interface? I need a blacklist of those symbols so that
> user (and perf-probe) can check which function can not be probed.
>
> It is just calling kprobe_add_area_blacklist() like below.
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2625c241ac00..4835b644bd2b 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2212,6 +2212,10 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
>  	ret = kprobe_add_area_blacklist((unsigned long)__kprobes_text_start,
>  					(unsigned long)__kprobes_text_end);
>  
> +	/* Symbols in noinstr section are blacklisted */
> +	ret = kprobe_add_area_blacklist((unsigned long)__noinstr_text_start,
> +					(unsigned long)__noinstr_text_end);
> +
>  	return ret ? : arch_populate_kprobe_blacklist();
>  }

So that extra function is not required when adding that, right?

>> +/* Functions in .noinstr.text must not be probed */
>> +static bool within_noinstr_text(unsigned long addr)
>> +{
>> +	/* FIXME: Handle module .noinstr.text */
>> +	return addr >= (unsigned long)__noinstr_text_start &&
>> +	       addr < (unsigned long)__noinstr_text_end;
>> +}
>> +
>>  bool within_kprobe_blacklist(unsigned long addr)
>>  {
>>  	char symname[KSYM_NAME_LEN], *p;
>>  
>> +	if (within_noinstr_text(addr))
>> +		return true;
>> +
>>  	if (__within_kprobe_blacklist(addr))
>>  		return true;