[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: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 10005bc92a316000321e89ea87a76d3e7599b1ea..669756bc20a220faebad33b63c268f5ca6add844 100644 (file)
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -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;
 

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 34a885bb82e0d94a38a7ebec8e8014cf2dc197d1..3ea6325228dafd293b8421ac4d47ea49457b17a0 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -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))))
-               return -EINVAL;
+       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 @@ valid_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;
 }