kprobes: kretprobe user entry-handler

Provide support to add an optional user defined callback to be run at
function entry of a kretprobe'd function.  Also modify the kprobe smoke
tests to include an entry-handler during the kretprobe sanity test.

Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Acked-by: Jim Keniston <jkenisto@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 22 insertions, 3 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d0493eafea3..7a86e643233 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -699,6 +699,12 @@ static int __kprobes pre_handler_kretprobe(struct kprobe *p,
 				 struct kretprobe_instance, uflist);
 		ri->rp = rp;
 		ri->task = current;
+
+		if (rp->entry_handler && rp->entry_handler(ri, regs)) {
+			spin_unlock_irqrestore(&kretprobe_lock, flags);
+			return 0;
+		}
+
 		arch_prepare_kretprobe(ri, regs);
 
 		/* XXX(hch): why is there no hlist_move_head? */
@@ -745,7 +751,8 @@ int __kprobes register_kretprobe(struct kretprobe *rp)
 	INIT_HLIST_HEAD(&rp->used_instances);
 	INIT_HLIST_HEAD(&rp->free_instances);
 	for (i = 0; i < rp->maxactive; i++) {
-		inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
+		inst = kmalloc(sizeof(struct kretprobe_instance) +
+			       rp->data_size, GFP_KERNEL);
 		if (inst == NULL) {
 			free_rp_inst(rp);
 			return -ENOMEM;
diff --git a/kernel/test_kprobes.c b/kernel/test_kprobes.c
index 88cdb109e13..06b6395b45b 100644
--- a/kernel/test_kprobes.c
+++ b/kernel/test_kprobes.c
@@ -135,6 +135,12 @@ static int test_jprobe(void)
 #ifdef CONFIG_KRETPROBES
 static u32 krph_val;
 
+static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+	krph_val = (rand1 / div_factor);
+	return 0;
+}
+
 static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
 {
 	unsigned long ret = regs_return_value(regs);
@@ -144,13 +150,19 @@ static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
 		printk(KERN_ERR "Kprobe smoke test failed: "
 				"incorrect value in kretprobe handler\n");
 	}
+	if (krph_val == 0) {
+		handler_errors++;
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"call to kretprobe entry handler failed\n");
+	}
 
-	krph_val = (rand1 / div_factor);
+	krph_val = rand1;
 	return 0;
 }
 
 static struct kretprobe rp = {
 	.handler	= return_handler,
+	.entry_handler  = entry_handler,
 	.kp.symbol_name = "kprobe_target"
 };
 
@@ -167,7 +179,7 @@ static int test_kretprobe(void)
 
 	ret = kprobe_target(rand1);
 	unregister_kretprobe(&rp);
-	if (krph_val == 0) {
+	if (krph_val != rand1) {
 		printk(KERN_ERR "Kprobe smoke test failed: "
 				"kretprobe handler not called\n");
 		handler_errors++;