tracing: kprobe: Check kretprobe offset from symbol correctly

From: Masami Hiramatsu <mhiramat@kernel.org>

Check the kretprobe event offset from the nearest symbol correctly
instead of checking given offset value.
This will allow users to specify the relative offset from _text
or _stext so that they can put a kretprobe on one of same-name
functions.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 include/linux/kprobes.h     |    9 +++++++++
 kernel/kprobes.c            |    9 ---------
 kernel/trace/trace_kprobe.c |   18 +++++++++++++++++-
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 862f87a..6a92734 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -44,6 +44,15 @@
 #ifdef CONFIG_KPROBES
 #include <asm/kprobes.h>
 
+/*
+ * Some oddball architectures like 64bit powerpc have function descriptors
+ * so this must be overridable.
+ */
+#ifndef kprobe_lookup_name
+#define kprobe_lookup_name(name, addr) \
+	addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
+#endif
+
 /* kprobe_status settings */
 #define KPROBE_HIT_ACTIVE	0x00000001
 #define KPROBE_HIT_SS		0x00000002
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index a77f9d7..9236f3f 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -58,15 +58,6 @@
 #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
 
 
-/*
- * Some oddball architectures like 64bit powerpc have function descriptors
- * so this must be overridable.
- */
-#ifndef kprobe_lookup_name
-#define kprobe_lookup_name(name, addr) \
-	addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
-#endif
-
 static int kprobes_initialized;
 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c60f9dc..59f2b2f 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -587,6 +587,22 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
 	return NOTIFY_DONE;
 }
 
+static bool function_offset_within_entry(const char *sym, unsigned long offs)
+{
+	void *addr = NULL;
+
+	kprobe_lookup_name(sym, addr);
+	if (!addr)
+		return false;
+	addr += offs;
+
+	if (kallsyms_lookup_size_offset((unsigned long)addr, NULL, &offs) &&
+	    offs == 0)
+		return true;
+
+	return false;
+}
+
 static struct notifier_block trace_kprobe_module_nb = {
 	.notifier_call = trace_kprobe_module_callback,
 	.priority = 1	/* Invoked after kprobe module callback */
@@ -695,7 +711,7 @@ static int create_trace_kprobe(int argc, char **argv)
 			return ret;
 		}
 		if (offset && is_return &&
-		    !arch_function_offset_within_entry(offset)) {
+		    !function_offset_within_entry(symbol, offset)) {
 			pr_info("Given offset is not valid for return probe.\n");
 			return -EINVAL;
 		}