Re: [PATCH v3 3/3] kprobes: Flag out CONFIG_MODULES dependent code

[Masami Hiramatsu]

Hi Jarkko,

On Wed, 15 Jul 2020 01:32:29 +0300
Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:

> Remove CONFIG_MODULES dependency by flagging out the dependent code. This
> allows to use kprobes in a kernel without support for loadable modules,
> which could be useful for a test kernel or perhaps an embedded kernel.
> 

OK, looks good, I just have 2 comments below.

> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> ---
>  include/linux/module.h      | 14 +++++++-------
>  kernel/kprobes.c            |  7 +++++++
>  kernel/trace/trace_kprobe.c | 16 +++++++++++++++-
>  3 files changed, 29 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 857b84bf9e90..eaa8ad02f75c 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -290,6 +290,13 @@ extern typeof(name) __mod_##type##__##name##_device_table		\
>  
>  struct notifier_block;
>  
> +enum module_state {
> +	MODULE_STATE_LIVE,	/* Normal state. */
> +	MODULE_STATE_COMING,	/* Full formed, running module_init. */
> +	MODULE_STATE_GOING,	/* Going away. */
> +	MODULE_STATE_UNFORMED,	/* Still setting it up. */
> +};
> +
>  #ifdef CONFIG_MODULES
>  
>  extern int modules_disabled; /* for sysctl */
> @@ -305,13 +312,6 @@ struct module_use {
>  	struct module *source, *target;
>  };
>  
> -enum module_state {
> -	MODULE_STATE_LIVE,	/* Normal state. */
> -	MODULE_STATE_COMING,	/* Full formed, running module_init. */
> -	MODULE_STATE_GOING,	/* Going away. */
> -	MODULE_STATE_UNFORMED,	/* Still setting it up. */
> -};
> -
>  struct mod_tree_node {
>  	struct module *mod;
>  	struct latch_tree_node node;
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index b4f3c24cd2ef..3039df13d34e 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2225,6 +2225,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_MODULES
>  /* Remove all symbols in given area from kprobe blacklist */
>  static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
>  {
> @@ -2242,6 +2243,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
>  {
>  	kprobe_remove_area_blacklist(entry, entry + 1);
>  }
> +#endif
>  
>  int __init __weak arch_populate_kprobe_blacklist(void)
>  {
> @@ -2285,6 +2287,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
>  	return ret ? : arch_populate_kprobe_blacklist();
>  }
>  
> +#ifdef CONFIG_MODULES
>  static void add_module_kprobe_blacklist(struct module *mod)
>  {
>  	unsigned long start, end;
> @@ -2330,6 +2333,10 @@ static void remove_module_kprobe_blacklist(struct module *mod)
>  		kprobe_remove_area_blacklist(start, end);
>  	}
>  }
> +#else
> +static void add_module_kprobe_blacklist(struct module *mod) {}
> +static void remove_module_kprobe_blacklist(struct module *mod) {}
> +#endif /* CONFIG_MODULES */

Please feel free to move the function. I would like to see;

#ifdef CONFIG_MODULES
/* Remove all symbols in given area from kprobe blacklist */
static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
{
...
}
static void add_module_kprobe_blacklist(struct module *mod)
{
...
}
#else
static void add_module_kprobe_blacklist(struct module *mod) {}
static void remove_module_kprobe_blacklist(struct module *mod) {}
#endif /* CONFIG_MODULES */

Rather than split #ifdefs.

>  
>  /* Module notifier call back, checking kprobes on the module */
>  static int kprobes_module_callback(struct notifier_block *nb,
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 710ec6a6aa8f..7fcd1bf2d96e 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -103,8 +103,9 @@ static nokprobe_inline bool trace_kprobe_has_gone(struct trace_kprobe *tk)
>  	return !!(kprobe_gone(&tk->rp.kp));
>  }
>  
> +#ifdef CONFIG_MODULES
>  static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> -						 struct module *mod)
> +						       struct module *mod)
>  {
>  	int len = strlen(mod->name);
>  	const char *name = trace_kprobe_symbol(tk);
> @@ -129,6 +130,17 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
>  
>  	return ret;
>  }
> +#else
> +static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> +						       struct module *mod)
> +{
> +	return false;
> +}
> +static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> +{
> +	return false;
> +}
> +#endif
>  
>  static bool trace_kprobe_is_busy(struct dyn_event *ev)
>  {
> @@ -685,10 +697,12 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
>  			/* Don't need to check busy - this should have gone. */
>  			__unregister_trace_kprobe(tk);
>  			ret = __register_trace_kprobe(tk);
> +#ifdef CONFIG_MODULES
>  			if (ret)
>  				pr_warn("Failed to re-register probe %s on %s: %d\n",
>  					trace_probe_name(&tk->tp),
>  					mod->name, ret);
> +#endif

I guess this CONFIG_MODULES is for avoiding build error according to mod->name,
if so, please use module_name(mod) macro instead of this #ifdef.

>  		}
>  	}
>  	mutex_unlock(&event_mutex);
> -- 
> 2.25.1
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>