uretprobes: register, unregister uretprobesf17_uretprobes

A uretprobe is specified by a file:offset:handler. A uprobe is created
at the offset specified. When this uprobe is hit a uretprobe instance
would be created and a probe placed instead of the return address of the
current function. The handler specified is invoked before replacing the
return address. A uretprobe therefore places two probes, firstly a
uprobe at offset, whose handler in turn places the second probe at the
return address at task runtime.

Signed-off-by: Anithra P Janakiraman <anithra@linux.vnet.ibm.com>
Signed-off-by: Anton Arapov <anton@redhat.com>

2 files changed, 158 insertions, 0 deletions

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 6c1cf58..c73d6c5 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -122,6 +122,8 @@ extern void uprobe_notify_resume(struct pt_regs *regs);
 extern bool uprobe_deny_signal(void);
 extern bool __weak arch_uprobe_skip_sstep(struct arch_uprobe *aup, struct pt_regs *regs);
 extern void uprobe_clear_state(struct mm_struct *mm);
+extern int uretprobe_register(struct inode *inode, loff_t offset, struct uretprobe_consumer *consumer);
+extern void uretprobe_unregister(struct inode *inode, loff_t offset, struct uretprobe_consumer *consumer);
 #else /* !CONFIG_UPROBES */
 struct uprobes_state {
 };
@@ -166,5 +168,14 @@ static inline void uprobe_copy_process(struct task_struct *t)
 static inline void uprobe_clear_state(struct mm_struct *mm)
 {
 }
+static inline int
+uretprobe_register(struct inode *inode, loff_t offset, struct uretprobe_consumer *consumer)
+{
+	return -ENOSYS;
+}
+static inline void
+uretprobe_unregister(struct inode *inode, loff_t offset, struct uretprobe_consumer *consumer)
+{
+}
 #endif /* !CONFIG_UPROBES */
 #endif	/* _LINUX_UPROBES_H */
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 6b619a3..776fd62 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -650,6 +650,45 @@ static bool consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
 	return ret;
 }
 
+/* Returns the previous uretprobe consumer */
+static struct uretprobe_consumer *
+uretprobe_consumer_add(struct uprobe *uprobe, struct uretprobe_consumer *rpc)
+{
+	struct uretprobe *rp;
+
+	rp = uprobe->rp;
+
+	down_write(&rp->consumer_rwsem);
+	rpc->next = rp->consumers;
+	rp->consumers = rpc;
+	up_write(&rp->consumer_rwsem);
+
+	return rpc->next;
+}
+
+/*
+ * For uretprobe @uretprobe, delete the consumer @urc.
+ * Return true if the @urc is deleted successfully or return false.
+ */
+static bool
+uretprobe_consumer_del(struct uretprobe *rp, struct uretprobe_consumer *rpc)
+{
+	struct uretprobe_consumer **con;
+	bool ret = false;
+
+	down_write(&rp->consumer_rwsem);
+	for (con = &rp->consumers; *con; con = &(*con)->next) {
+		if (*con == rpc) {
+			*con = rpc->next;
+			ret = true;
+			break;
+		}
+	}
+	up_write(&rp->consumer_rwsem);
+
+	return ret;
+}
+
 static int
 __copy_insn(struct address_space *mapping, struct file *filp, char *insn,
 			unsigned long nbytes, loff_t offset)
@@ -1032,6 +1071,114 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume
 		put_uprobe(uprobe);
 }
 
+/*
+ * uretprobe_register - register return probe
+ * @inode: the file in which the probe has to be placed.
+ * @offset: offset from the start of the file.
+ * @urc: information on howto handle the probe.
+ *
+ * Return  errno if it cannot successully install probes else
+ * return 0 (success)
+ */
+int uretprobe_register(struct inode *inode, loff_t offset, struct uretprobe_consumer *urc)
+{
+	struct uretprobe *rp;
+	struct uprobe_consumer *uc;
+	struct uprobe *uprobe;
+
+	if (!inode || !urc || urc->next)
+		return -EINVAL;
+
+	uprobe = find_uprobe(inode, offset);
+	if (uprobe) {
+		uc = uprobe->consumers;
+		if (!uc)
+			return -EINVAL;
+
+		/*
+		 * uprobe already exists, it could have uprobe and or uretprobe
+		 * consumers. If there is a uretprobe consumer and uretprobe
+		 * structure already exists.
+		 */
+		while (uc) {
+			if (uc == uretprobe_dummy_consumer) {
+				rp = uprobe->rp;
+				goto uretprobe_consumer_add;
+			}
+			uc = uc->next;
+		}
+	}
+
+	/*
+	 * We have reached here because either there is no uprobe or the uprobe
+	 * does not have a uretprobe consumer yet
+	 */
+	if (!uretprobe_dummy_consumer) {
+		uretprobe_dummy_consumer =
+			kzalloc(sizeof(struct uprobe_consumer), GFP_KERNEL);
+		uretprobe_dummy_consumer->handler = NULL;
+		uretprobe_dummy_consumer->filter = NULL;
+	}
+	if (uprobe_register(inode, offset, uretprobe_dummy_consumer))
+		return -EINVAL;
+
+
+	uprobe = find_uprobe(inode, offset);
+	rp = kzalloc(sizeof(struct uretprobe), GFP_KERNEL);
+	rp->consumers = NULL;
+	init_rwsem(&rp->consumer_rwsem);
+	uprobe->rp = rp;
+
+ uretprobe_consumer_add:
+	uretprobe_consumer_add(uprobe, urc);
+	put_uprobe(uprobe);
+
+	return 0;
+}
+
+void uretprobe_unregister(struct inode *inode, loff_t offset, struct uretprobe_consumer *rpc)
+{
+	struct uprobe *uprobe;
+	struct uretprobe *rp = NULL;
+	struct uprobe_consumer *uc;
+
+	if (!inode || !rpc)
+		return;
+
+	uprobe = find_uprobe(inode, offset);
+	if (!uprobe) {
+		printk(KERN_ERR "No uprobe found with inode:offset %p %lld\n",
+				inode, offset);
+		return;
+	}
+
+	down_read(&uprobe->consumer_rwsem);
+	uc = uprobe->consumers;
+	while (uc) {
+		if (uc == uretprobe_dummy_consumer) {
+			rp = uprobe->rp;
+			break;
+		}
+		uc = uc->next;
+	}
+	up_read(&uprobe->consumer_rwsem);
+
+	if (!rp) {
+		printk(KERN_ERR "No uretprobe found with inode:offset %p %lld\n",
+				inode, offset);
+		goto unlock_uretprobe;
+	}
+	if (!uretprobe_consumer_del(rp, rpc))
+		goto unlock_uretprobe;
+	if (rp->consumers)
+		goto unlock_uretprobe;
+
+	uprobe_unregister(inode, offset, uretprobe_dummy_consumer);
+
+ unlock_uretprobe:
+	put_uprobe(uprobe);
+}
+
 static struct rb_node *
 find_node_in_range(struct inode *inode, loff_t min, loff_t max)
 {