Patch "rethook: Use __rcu pointer for rethook::handler" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    rethook: Use __rcu pointer for rethook::handler

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rethook-use-__rcu-pointer-for-rethook-handler.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From a1461f1fd6cfdc4b8917c9d4a91e92605d1f28dc Mon Sep 17 00:00:00 2001
From: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>
Date: Fri, 1 Dec 2023 14:53:56 +0900
Subject: rethook: Use __rcu pointer for rethook::handler

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

commit a1461f1fd6cfdc4b8917c9d4a91e92605d1f28dc upstream.

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().

NOTE: To avoid sparse warning, rethook::handler is defined by a raw
function pointer type with __rcu instead of rethook_handler_t.

Link: https://lore.kernel.org/all/170126066201.398836.837498688669005979.stgit@devnote2/

Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202311241808.rv9ceuAh-lkp@xxxxxxxxx/
Tested-by: JP Kobryn <inwardvessel@xxxxxxxxx>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/kprobes.h |    6 ++----
 include/linux/rethook.h |    7 ++++++-
 kernel/trace/rethook.c  |   23 ++++++++++++++---------
 3 files changed, 22 insertions(+), 14 deletions(-)

--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -202,10 +202,8 @@ extern int arch_trampoline_kprobe(struct
 #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)
 {
--- a/include/linux/rethook.h
+++ b/include/linux/rethook.h
@@ -29,7 +29,12 @@ typedef void (*rethook_handler_t) (struc
  */
 struct rethook {
 	void			*data;
-	rethook_handler_t	handler;
+	/*
+	 * To avoid sparse warnings, this uses a raw function pointer with
+	 * __rcu, instead of rethook_handler_t. But this must be same as
+	 * rethook_handler_t.
+	 */
+	void (__rcu *handler) (struct rethook_node *, void *, struct pt_regs *);
 	struct freelist_head	pool;
 	refcount_t		ref;
 	struct rcu_head		rcu;
--- a/kernel/trace/rethook.c
+++ b/kernel/trace/rethook.c
@@ -63,7 +63,7 @@ static void rethook_free_rcu(struct rcu_
  */
 void rethook_stop(struct rethook *rh)
 {
-	WRITE_ONCE(rh->handler, NULL);
+	rcu_assign_pointer(rh->handler, NULL);
 }
 
 /**
@@ -78,11 +78,17 @@ void rethook_stop(struct rethook *rh)
  */
 void rethook_free(struct rethook *rh)
 {
-	WRITE_ONCE(rh->handler, NULL);
+	rethook_stop(rh);
 
 	call_rcu(&rh->rcu, rethook_free_rcu);
 }
 
+static inline rethook_handler_t rethook_get_handler(struct rethook *rh)
+{
+	return (rethook_handler_t)rcu_dereference_check(rh->handler,
+							rcu_read_lock_any_held());
+}
+
 /**
  * rethook_alloc() - Allocate struct rethook.
  * @data: a data to pass the @handler when hooking the return.
@@ -102,7 +108,7 @@ struct rethook *rethook_alloc(void *data
 	}
 
 	rh->data = data;
-	rh->handler = handler;
+	rcu_assign_pointer(rh->handler, handler);
 	rh->pool.head = NULL;
 	refcount_set(&rh->ref, 1);
 
@@ -142,9 +148,10 @@ static void free_rethook_node_rcu(struct
  */
 void rethook_recycle(struct rethook_node *node)
 {
-	lockdep_assert_preemption_disabled();
+	rethook_handler_t handler;
 
-	if (likely(READ_ONCE(node->rethook->handler)))
+	handler = rethook_get_handler(node->rethook);
+	if (likely(handler))
 		freelist_add(&node->freelist, &node->rethook->pool);
 	else
 		call_rcu(&node->rcu, free_rethook_node_rcu);
@@ -160,11 +167,9 @@ NOKPROBE_SYMBOL(rethook_recycle);
  */
 struct rethook_node *rethook_try_get(struct rethook *rh)
 {
-	rethook_handler_t handler = READ_ONCE(rh->handler);
+	rethook_handler_t handler = rethook_get_handler(rh);
 	struct freelist_node *fn;
 
-	lockdep_assert_preemption_disabled();
-
 	/* Check whether @rh is going to be freed. */
 	if (unlikely(!handler))
 		return NULL;
@@ -312,7 +317,7 @@ unsigned long rethook_trampoline_handler
 		rhn = container_of(first, struct rethook_node, llist);
 		if (WARN_ON_ONCE(rhn->frame != frame))
 			break;
-		handler = READ_ONCE(rhn->rethook->handler);
+		handler = rethook_get_handler(rhn->rethook);
 		if (handler)
 			handler(rhn, rhn->rethook->data, regs);
 


Patches currently in stable-queue which might be from mhiramat@xxxxxxxxxx are

queue-6.1/rethook-use-__rcu-pointer-for-rethook-handler.patch
queue-6.1/kprobes-consistent-rcu-api-usage-for-kretprobe-holder.patch




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