Re: [PATCH 4/6] kprobes/ftrace: Use ftrace_location() when [dis]arming probes

[Steven Rostedt <rostedt@goodmis.org>]

On Sat, 13 Mar 2021 14:41:47 +0800
Huang Pei <huangpei@loongson.cn> wrote:

> From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
> 

Looks like this was sent before, but was missing the proper authorship
(which is not Jisheng).

   https://lore.kernel.org/linux-arm-kernel/20191225173219.4f9db436@xhacker.debian/

-- Steve


> 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.
> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  kernel/kprobes.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 41fdbb7953c6..66ee28b071c2 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1045,9 +1045,10 @@ static int prepare_kprobe(struct kprobe *p)
>  static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
>  			       int *cnt)
>  {
> +	unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
>  	int ret = 0;
>  
> -	ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 0, 0);
> +	ret = ftrace_set_filter_ip(ops, ftrace_ip, 0, 0);
>  	if (ret) {
>  		pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
>  			 p->addr, ret);
> @@ -1070,7 +1071,7 @@ static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
>  	 * At this point, sinec ops is not registered, we should be sefe from
>  	 * registering empty filter.
>  	 */
> -	ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
> +	ftrace_set_filter_ip(ops, ftrace_ip, 1, 0);
>  	return ret;
>  }
>  
> @@ -1087,6 +1088,7 @@ static int arm_kprobe_ftrace(struct kprobe *p)
>  static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
>  				  int *cnt)
>  {
> +	unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
>  	int ret = 0;
>  
>  	if (*cnt == 1) {
> @@ -1097,7 +1099,7 @@ static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
>  
>  	(*cnt)--;
>  
> -	ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
> +	ret = ftrace_set_filter_ip(ops, ftrace_ip, 1, 0);
>  	WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
>  		  p->addr, ret);
>  	return ret;