linux-kernel - Re: [PATCH 6/7] kprobes/ftrace: Use ftrace

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Message-Id: <20190621234140.5604fcd4ae5260b1020deccb@kernel.org>
Date:   Fri, 21 Jun 2019 23:41:40 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/7] kprobes/ftrace: Use ftrace_location() when
 [dis]arming probes

On Tue, 18 Jun 2019 20:17:05 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:

> Ftrace location could include more than a single instruction in case of
> some architectures (powerpc64, for now). In this case, kprobe is
> permitted on any of those instructions, and uses ftrace infrastructure
> for functioning.
> 
> However, [dis]arm_kprobe_ftrace() uses the kprobe address when setting
> up ftrace filter IP. This won't work if the address points to any
> instruction apart from the one that has a branch to _mcount(). To
> resolve this, have [dis]arm_kprobe_ftrace() use ftrace_function() to
> identify the filter IP.

This looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you!

> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> ---
>  kernel/kprobes.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 445337c107e0..282ee704e2d8 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -978,10 +978,10 @@ static int prepare_kprobe(struct kprobe *p)
>  /* Caller must lock kprobe_mutex */
>  static int arm_kprobe_ftrace(struct kprobe *p)
>  {
> +	unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
>  	int ret = 0;
>  
> -	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
> -				   (unsigned long)p->addr, 0, 0);
> +	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 0, 0);
>  	if (ret) {
>  		pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
>  			 p->addr, ret);
> @@ -1005,13 +1005,14 @@ static int arm_kprobe_ftrace(struct kprobe *p)
>  	 * non-empty filter_hash for IPMODIFY ops, we're safe from an accidental
>  	 * empty filter_hash which would undesirably trace all functions.
>  	 */
> -	ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0);
> +	ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 1, 0);
>  	return ret;
>  }
>  
>  /* Caller must lock kprobe_mutex */
>  static int disarm_kprobe_ftrace(struct kprobe *p)
>  {
> +	unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
>  	int ret = 0;
>  
>  	if (kprobe_ftrace_enabled == 1) {
> @@ -1022,8 +1023,7 @@ static int disarm_kprobe_ftrace(struct kprobe *p)
>  
>  	kprobe_ftrace_enabled--;
>  
> -	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
> -			   (unsigned long)p->addr, 1, 0);
> +	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 1, 0);
>  	WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
>  		  p->addr, ret);
>  	return ret;
> -- 
> 2.22.0
> 


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