linux-kernel - Re: [PATCH 2/2] kprobes: Mark ftrace mcount handler functions nokprobe

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Date:   Mon, 7 Jan 2019 15:55:36 +0100
From:   Andrea Righi <righi.andrea@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>, peterz@...radead.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/2] kprobes: Mark ftrace mcount handler functions
 nokprobe

On Mon, Jan 07, 2019 at 10:32:32PM +0900, Masami Hiramatsu wrote:
> Mark ftrace mcount handler functions nokprobe since
> probing on these functions with kretprobe pushes
> return address incorrectly on kretprobe shadow stack.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> Reported-by: Francis Deslauriers <francis.deslauriers@...icios.com>
> ---
>  kernel/trace/ftrace.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index f0ff24173a0b..ad4babad4a03 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6250,7 +6250,7 @@ void ftrace_reset_array_ops(struct trace_array *tr)
>  	tr->ops->func = ftrace_stub;
>  }
>  
> -static inline void
> +static nokprobe_inline void

I think we need to #include <linux/kprobes.h>, otherwise:

  CC      kernel/trace/ftrace.o
kernel/trace/ftrace.c:6219:24: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘void’
 static nokprobe_inline void
                        ^~~~

 kernel/trace/ftrace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3a58ad280d83..0333241034d5 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -32,6 +32,7 @@
 #include <linux/sort.h>
 #include <linux/list.h>
 #include <linux/hash.h>
+#include <linux/kprobes.h>
 #include <linux/rcupdate.h>
 
 #include <trace/events/sched.h>

Thanks,
-Andrea

>  __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
>  		       struct ftrace_ops *ignored, struct pt_regs *regs)
>  {
> @@ -6310,11 +6310,13 @@ static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
>  {
>  	__ftrace_ops_list_func(ip, parent_ip, NULL, regs);
>  }
> +NOKPROBE_SYMBOL(ftrace_ops_list_func);
>  #else
>  static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip)
>  {
>  	__ftrace_ops_list_func(ip, parent_ip, NULL, NULL);
>  }
> +NOKPROBE_SYMBOL(ftrace_ops_no_ops);
>  #endif
>  
>  /*
> @@ -6341,6 +6343,7 @@ static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip,
>  	preempt_enable_notrace();
>  	trace_clear_recursion(bit);
>  }
> +NOKPROBE_SYMBOL(ftrace_ops_assist_func);
>  
>  /**
>   * ftrace_ops_get_func - get the function a trampoline should call