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Commit df019b1d authored by Keshavamurthy Anil S's avatar Keshavamurthy Anil S Committed by Linus Torvalds
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[PATCH] kprobes: fix unloading of self probed module 



When a kprobes modules is written in such a way that probes are inserted on
itself, then unload of that moudle was not possible due to reference
couning on the same module.

The below patch makes a check and incrementes the module refcount only if
it is not a self probed module.

We need to allow modules to probe themself for kprobes performance
measurements

This patch has been tested on several x86_64, ppc64 and IA64 architectures.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent ef43bc4f

include/linux/kprobes.h

+3 −0
Original line number Diff line number Diff line
@@ -68,6 +68,9 @@ struct kprobe { 
	/* list of kprobes for multi-handler support */

	struct list_head list;



	/* Indicates that the corresponding module has been ref counted */

	unsigned int mod_refcounted;



	/*count the number of times this probe was temporarily disarmed */

	unsigned long nmissed;

kernel/kprobes.c

+32 −10
Original line number Diff line number Diff line
@@ -449,19 +449,32 @@ static int __kprobes in_kprobes_functions(unsigned long addr) 
	return 0;

}



int __kprobes register_kprobe(struct kprobe *p)

static int __kprobes __register_kprobe(struct kprobe *p,

	unsigned long called_from)

{

	int ret = 0;

	struct kprobe *old_p;

	struct module *mod;

	struct module *probed_mod;



	if ((!kernel_text_address((unsigned long) p->addr)) ||

		in_kprobes_functions((unsigned long) p->addr))

		return -EINVAL;



	if ((mod = module_text_address((unsigned long) p->addr)) &&

			(unlikely(!try_module_get(mod))))

	p->mod_refcounted = 0;

	/* Check are we probing a module */

	if ((probed_mod = module_text_address((unsigned long) p->addr))) {

		struct module *calling_mod = module_text_address(called_from);

		/* We must allow modules to probe themself and

		 * in this case avoid incrementing the module refcount,

		 * so as to allow unloading of self probing modules.

		 */

		if (calling_mod && (calling_mod != probed_mod)) {

			if (unlikely(!try_module_get(probed_mod)))

				return -EINVAL;

			p->mod_refcounted = 1;

		} else

			probed_mod = NULL;

	}



	p->nmissed = 0;

	down(&kprobe_mutex);
@@ -483,11 +496,17 @@ int __kprobes register_kprobe(struct kprobe *p) 
out:

	up(&kprobe_mutex);



	if (ret && mod)

		module_put(mod);

	if (ret && probed_mod)

		module_put(probed_mod);

	return ret;

}



int __kprobes register_kprobe(struct kprobe *p)

{

	return __register_kprobe(p,

		(unsigned long)__builtin_return_address(0));

}



void __kprobes unregister_kprobe(struct kprobe *p)

{

	struct module *mod;
@@ -524,7 +543,8 @@ void __kprobes unregister_kprobe(struct kprobe *p) 
	up(&kprobe_mutex);



	synchronize_sched();

	if ((mod = module_text_address((unsigned long)p->addr)))

	if (p->mod_refcounted &&

	    (mod = module_text_address((unsigned long)p->addr)))

		module_put(mod);



	if (cleanup_p) {
@@ -547,7 +567,8 @@ int __kprobes register_jprobe(struct jprobe *jp) 
	jp->kp.pre_handler = setjmp_pre_handler;

	jp->kp.break_handler = longjmp_break_handler;



	return register_kprobe(&jp->kp);

	return __register_kprobe(&jp->kp,

		(unsigned long)__builtin_return_address(0));

}



void __kprobes unregister_jprobe(struct jprobe *jp)
@@ -587,7 +608,8 @@ int __kprobes register_kretprobe(struct kretprobe *rp) 


	rp->nmissed = 0;

	/* Establish function entry probe point */

	if ((ret = register_kprobe(&rp->kp)) != 0)

	if ((ret = __register_kprobe(&rp->kp,

		(unsigned long)__builtin_return_address(0))) != 0)

		free_rp_inst(rp);

	return ret;

}