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

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Message-Id: <20220928002221.ddda8e26e3034180e33ad24e@kernel.org>
Date:   Wed, 28 Sep 2022 00:22:21 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Liao Chang <liaochang1@...wei.com>, <mingo@...hat.com>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <linux-kernel@...r.kernel.org>,
        <linux-riscv@...ts.infradead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH] kprobes: Mark ftrace mcount handler functions nokprobe

On Mon, 26 Sep 2022 14:37:23 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 19 Sep 2022 16:45:33 +0800
> Liao Chang <liaochang1@...wei.com> wrote:
> 
> > Mark ftrace mcount handler functions nokprobe since probing on these
> > functions probably reaches mcount recursivly during kprobe breakpoint
> > handler for some architecture(tested for riscv, arm64), and reenter
> > kprobe is treated as a fatal error, causes kernel panic.
> 
> This looks to me that the affected archs should be made more robust for this
> case than to add this to the generic code.

Yeah, kprobes (arch specific code) itself shouldn't be traced by ftrace usually.

Thank you,

> 
> -- Steve
> 
> 
> > 
> > Pesudo code below demonstrate this problem:
> > 
> >   mcount
> >     function_trace_call (probed)
> >       arch_breakpoint_handler
> >         arch_setup_singlestep [mcount]
> >           function_trace_call (probed)
> >             arch_breakpoint_handler
> >               reenter_kprobe
> >                 BUG
> > 
> > Signed-off-by: Liao Chang <liaochang1@...wei.com>
> > ---
> >  kernel/trace/trace_functions.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> > index 9f1bfbe105e8..440a678a8c7c 100644
> > --- a/kernel/trace/trace_functions.c
> > +++ b/kernel/trace/trace_functions.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/ftrace.h>
> >  #include <linux/slab.h>
> >  #include <linux/fs.h>
> > +#include <linux/kprobes.h>
> >  
> >  #include "trace.h"
> >  
> > @@ -194,6 +195,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
> >  
> >  	ftrace_test_recursion_unlock(bit);
> >  }
> > +NOKPROBE_SYMBOL(function_trace_call);
> >  
> >  #ifdef CONFIG_UNWINDER_ORC
> >  /*
> > @@ -245,6 +247,7 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
> >  	atomic_dec(&data->disabled);
> >  	local_irq_restore(flags);
> >  }
> > +NOKPROBE_SYMBOL(function_stack_trace_call);
> >  
> >  static inline bool is_repeat_check(struct trace_array *tr,
> >  				   struct trace_func_repeats *last_info,
> > @@ -321,6 +324,7 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> >  out:
> >  	ftrace_test_recursion_unlock(bit);
> >  }
> > +NOKPROBE_SYMBOL(function_no_repeats_trace_call);
> >  
> >  static void
> >  function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> > @@ -363,6 +367,7 @@ function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> >  	atomic_dec(&data->disabled);
> >  	local_irq_restore(flags);
> >  }
> > +NOKPROBE_SYMBOL(function_stack_no_repeats_trace_call);
> >  
> >  static struct tracer_opt func_opts[] = {
> >  #ifdef CONFIG_STACKTRACE
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>