From: "Masami Hiramatsu (Google)" mhiramat@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().
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@dev...
Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook") Cc: stable@vger.kernel.org Reported-by: kernel test robot lkp@intel.com Closes: https://lore.kernel.org/oe-kbuild-all/202311241808.rv9ceuAh-lkp@intel.com/ Tested-by: JP Kobryn inwardvessel@gmail.com Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org (cherry picked from commit a1461f1fd6cfdc4b8917c9d4a91e92605d1f28dc) --- include/linux/kprobes.h | 6 ++---- include/linux/rethook.h | 7 ++++++- kernel/trace/rethook.c | 23 ++++++++++++++--------- 3 files changed, 22 insertions(+), 14 deletions(-)
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h index 85a64cb95d75..38a774287bde 100644 --- a/include/linux/kprobes.h +++ b/include/linux/kprobes.h @@ -202,10 +202,8 @@ 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 26b6f3c81a76..544e1bbfad28 100644 --- a/include/linux/rethook.h +++ b/include/linux/rethook.h @@ -29,7 +29,12 @@ typedef void (*rethook_handler_t) (struct rethook_node *, void *, unsigned long, */ 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 *, unsigned long, struct pt_regs *); struct freelist_head pool; refcount_t ref; struct rcu_head rcu; diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c index 5eb9b598f4e9..3cebcbaf35a4 100644 --- a/kernel/trace/rethook.c +++ b/kernel/trace/rethook.c @@ -63,7 +63,7 @@ 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); }
/** @@ -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, rethook_handler_t handler) }
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 rcu_head *head) */ 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(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 = rethook_get_handler(rhn->rethook); if (handler) handler(rhn, rhn->rethook->data, correct_ret_addr, regs);