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

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Date:   Mon, 23 Mar 2020 23:00:25 +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>,
        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

Hi Thomas,

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();
 }
 
Thank you,


> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  kernel/kprobes.c |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1443,10 +1443,21 @@ static bool __within_kprobe_blacklist(un
>  	return false;
>  }
>  
> +/* 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;
>  
> 


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