Subject: [PATCH 25/35] kretprobes: Ensure probe location is at function entry

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Mon, 6 Mar 2017 16:38:15 -0300

From: "Naveen N. Rao" <[email-masked]>

kretprobes can be registered by specifying an absolute address or by
specifying offset to a symbol. However, we need to ensure this falls at
function entry so as to be able to determine the return address.

Validate the same during kretprobe registration. By default, there
should not be any offset from a function entry, as determined through a
kallsyms_lookup(). Introduce arch_function_offset_within_entry() as a
way for architectures to override this.

Signed-off-by: Naveen N. Rao <[email-masked]>
Acked-by: Masami Hiramatsu <[email-masked]>
Cc: Ananth N Mavinakayanahalli <[email-masked]>
Cc: Michael Ellerman <[email-masked]>
Cc: Steven Rostedt <[email-masked]>
Cc: [email-masked]
Link: http://lkml.kernel.org/r/f158[email-masked]
Signed-off-by: Arnaldo Carvalho de Melo <[email-masked]>
---
 include/linux/kprobes.h |  1 +
 kernel/kprobes.c        | 13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index c328e4f7dcad..177bdf6c6aeb 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -267,6 +267,7 @@ extern int arch_init_kprobes(void);
 extern void show_registers(struct pt_regs *regs);
 extern void kprobes_inc_nmissed_count(struct kprobe *p);
 extern bool arch_within_kprobe_blacklist(unsigned long addr);
+extern bool arch_function_offset_within_entry(unsigned long offset);
 
 extern bool within_kprobe_blacklist(unsigned long addr);
 
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 699c5bc51a92..448759d4a263 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1875,12 +1875,25 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(pre_handler_kretprobe);
 
+bool __weak arch_function_offset_within_entry(unsigned long offset)
+{
+	return !offset;
+}
+
 int register_kretprobe(struct kretprobe *rp)
 {
 	int ret = 0;
 	struct kretprobe_instance *inst;
 	int i;
 	void *addr;
+	unsigned long offset;
+
+	addr = kprobe_addr(&rp->kp);
+	if (!kallsyms_lookup_size_offset((unsigned long)addr, NULL, &offset))
+		return -EINVAL;
+
+	if (!arch_function_offset_within_entry(offset))
+		return -EINVAL;
 
 	if (kretprobe_blacklist_size) {
 		addr = kprobe_addr(&rp->kp);
-- 
2.9.3