linux-kernel - Re: [PATCH tip/master 1/3] kprobes: Support blacklist functions in module

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Message-ID: <55AB166B.9040509@hitachi.com>
Date:	Sun, 19 Jul 2015 12:15:55 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Pratyush Anand <panand@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, Rob Landley <rob@...dley.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH tip/master 1/3] kprobes: Support blacklist functions in
 module

On 2015/07/17 21:10, Ingo Molnar wrote:
> 
> * Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
> 
>> To blacklist the functions in a module (e.g. user-defined
>> kprobe handler and the functions invoked from it), expand
>> blacklist support for modules.
>> With this change, users can use NOKPROBE_SYMBOL() macro in
>> their own modules.
> 
> Btw., whatever happened with renaming '__kprobes' to '__nokprobe' and using that 
> consistently to blacklist certain functions?

Yes, in this part, __kprobes marked functions placed in .kprobes.text section
are safely added to the blacklist :)

-----
+       if (err >= 0 && __kprobes_text_start != __kprobes_text_end) {
+               /* The __kprobes marked functions must not be probed */
+               err = kprobe_blacklist_add_range(
+                                       (unsigned long)__kprobes_text_start,
+                                       (unsigned long)__kprobes_text_end);
+       }
-----


> 
> Also, shouldn't we convert such instances:
> 
> 	static int notifier_call_chain(struct notifier_block **nl,
>                                unsigned long val, void *v,
>                                int nr_to_call, int *nr_calls)
> 
> 	...
> 
> 	NOKPROBE_SYMBOL(notifier_call_chain);
> 
> to:
> 
> 	static int __nokprobe notifier_call_chain(struct notifier_block **nl,
>                                unsigned long val, void *v,
>                                int nr_to_call, int *nr_calls)
> 
> ?

For some symbols we can do that. But it can conflict with other __section
attributes e.g. __sched, since a function must be placed in only one
section. So, IMHO, using section for expressing its attribute is not
a good idea, but I couldn't find another option in common function attribute.

https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes

Thus I've introduced NOKPROBE_SYMBOL macro which stores the target function
addresses (not the function itself) in the _kprobe_blacklist section.

Thank you,

> 
> I.e. instead of extending it to modules we should eliminate NOKPROBE_SYMBOL() in 
> favor of marking functions as __nokprobe which is the standard syntax for marking 
> functions.
> 
> Thanks,
> 
> 	Ingo
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com
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