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 d0493eafea3e..7a86e6432338 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 88cdb109e13c..06b6395b45b2 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++;