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

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Date:   Tue, 24 Mar 2020 14:49:53 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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>,
        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

On Mon, 23 Mar 2020 17:03:24 +0100
Thomas Gleixner <tglx@...utronix.de> wrote:

> 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?

That's right :)

> 
> >> +/* Functions in .noinstr.text must not be probed */
> >> +static bool within_noinstr_text(unsigned long addr)
> >> +{
> >> +	/* FIXME: Handle module .noinstr.text */

And this reminds me that the module .kprobes.text is not handled yet :(.

Thank you,

> >> +	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;


-- 
Masami Hiramatsu <mhiramat@...nel.org>