From: Masami Hiramatsu (Google) <mhira...@kernel.org>
Since the rethook::handler is an RCU-maganged pointer so that it will
notice readers the rethook is stopped (unregistered) or not, it should
be an __rcu pointer and use appropriate functions to be accessed. This
will use appropriate memory barrier when accessing it. OTOH, rethook::data
is never changed, so we don't need to check it in get_kretprobe().
Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
---
include/linux/kprobes.h | 6 ++----
include/linux/rethook.h | 2 +-
kernel/trace/rethook.c | 21 ++++++++++++---------
3 files changed, 15 insertions(+), 14 deletions(-)
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 64672bace560..0ff44d6633e3 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -197,10 +197,8 @@ extern int arch_trampoline_kprobe(struct kprobe *p);
#ifdef CONFIG_KRETPROBE_ON_RETHOOK
static nokprobe_inline struct kretprobe *get_kretprobe(struct
kretprobe_instance *ri)
{
- RCU_LOCKDEP_WARN(!rcu_read_lock_any_held(),
- "Kretprobe is accessed from instance under preemptive context");
-
- return (struct kretprobe *)READ_ONCE(ri->node.rethook->data);
+ /* rethook::data is non-changed field, so that you can access it
freely. */
+ return (struct kretprobe *)ri->node.rethook->data;
}
static nokprobe_inline unsigned long get_kretprobe_retaddr(struct
kretprobe_instance *ri)
{
diff --git a/include/linux/rethook.h b/include/linux/rethook.h
index ce69b2b7bc35..164cd32c25cd 100644
--- a/include/linux/rethook.h
+++ b/include/linux/rethook.h
@@ -28,7 +28,7 @@ typedef void (*rethook_handler_t) (struct rethook_node *,
void *, unsigned long,
*/
struct rethook {
void *data;
- rethook_handler_t handler;
+ rethook_handler_t __rcu handler;
struct objpool_head pool;
struct rcu_head rcu;
};
diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
index 6fd7d4ecbbc6..77f0e987bbff 100644
--- a/kernel/trace/rethook.c
+++ b/kernel/trace/rethook.c
@@ -48,7 +48,7 @@ static void rethook_free_rcu(struct rcu_head *head)
*/
void rethook_stop(struct rethook *rh)
{
- WRITE_ONCE(rh->handler, NULL);
+ rcu_assign_pointer(rh->handler, NULL);
}
/**
@@ -63,7 +63,7 @@ void rethook_stop(struct rethook *rh)
*/
void rethook_free(struct rethook *rh)
{
- WRITE_ONCE(rh->handler, NULL);
+ rcu_assign_pointer(rh->handler, NULL);
call_rcu(&rh->rcu, rethook_free_rcu);
}
@@ -107,7 +107,7 @@ struct rethook *rethook_alloc(void *data, rethook_handler_t
handler,
return ERR_PTR(-ENOMEM);
rh->data = data;
- rh->handler = handler;
+ rcu_assign_pointer(rh->handler, handler);
/* initialize the objpool for rethook nodes */
if (objpool_init(&rh->pool, num, size, GFP_KERNEL, rh,
@@ -135,9 +135,12 @@ static void free_rethook_node_rcu(struct rcu_head *head)
*/
void rethook_recycle(struct rethook_node *node)
{
- lockdep_assert_preemption_disabled();
+ rethook_handler_t handler;
+
+ handler = rcu_dereference_check(node->rethook->handler,
+ rcu_read_lock_any_held());
- if (likely(READ_ONCE(node->rethook->handler)))
+ if (likely(handler))
objpool_push(node, &node->rethook->pool);
else
call_rcu(&node->rcu, free_rethook_node_rcu);
@@ -153,10 +156,9 @@ NOKPROBE_SYMBOL(rethook_recycle);
*/
struct rethook_node *rethook_try_get(struct rethook *rh)
{
- rethook_handler_t handler = READ_ONCE(rh->handler);
-
- lockdep_assert_preemption_disabled();
+ rethook_handler_t handler;
+ handler = rcu_dereference_check(rh->handler, rcu_read_lock_any_held());
/* Check whether @rh is going to be freed. */
if (unlikely(!handler))
return NULL;
@@ -300,7 +302,8 @@ unsigned long rethook_trampoline_handler(struct pt_regs
*regs,
rhn = container_of(first, struct rethook_node, llist);
if (WARN_ON_ONCE(rhn->frame != frame))
break;
- handler = READ_ONCE(rhn->rethook->handler);
+ handler = rcu_dereference_check(rhn->rethook->handler,
+ rcu_read_lock_any_held());
if (handler)
handler(rhn, rhn->rethook->data,
correct_ret_addr, regs);
