linux-kernel - [RFC 3/4] kprobes: Add a RCU lock while invoking __module_text

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Message-Id: <1438362488-29857-4-git-send-email-bigeasy@linutronix.de>
Date:	Fri, 31 Jul 2015 19:08:07 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	tglx@...utronix.de,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [RFC 3/4] kprobes: Add a RCU lock while invoking __module_text_address()

delete_module() first sets the module's state to MODULE_STATE_GOING
which means further try_module_get() invocations will fail. However
without a RCU readlock there is nothing that ensures that the pointer
returned by __module_text_address() is still valid in try_module_get().
The preempt_disable() does not protect here against module removal from
another CPU.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/kprobes.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c90e417bb963..a2d4e5164d7d 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1449,6 +1449,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 	}
 
 	/* Check if are we probing a module */
+	rcu_read_lock();
 	*probed_mod = __module_text_address((unsigned long) p->addr);
 	if (*probed_mod) {
 		/*
@@ -1457,7 +1458,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 		 */
 		if (unlikely(!try_module_get(*probed_mod))) {
 			ret = -ENOENT;
-			goto out;
+			goto out_rcu_unlock;
 		}
 
 		/*
@@ -1471,6 +1472,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
 			ret = -ENOENT;
 		}
 	}
+out_rcu_unlock:
+	rcu_read_unlock();
 out:
 	preempt_enable();
 	jump_label_unlock();
-- 
2.4.6

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