From e91c2518a5d22a07642f35d85f39001ad379dae4 Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Mon, 16 Apr 2018 13:36:46 +0200 Subject: livepatch: Initialize shadow variables safely by a custom callback The existing API allows to pass a sample data to initialize the shadow data. It works well when the data are position independent. But it fails miserably when we need to set a pointer to the shadow structure itself. Unfortunately, we might need to initialize the pointer surprisingly often because of struct list_head. It is even worse because the list might be hidden in other common structures, for example, struct mutex, struct wait_queue_head. For example, this was needed to fix races in ALSA sequencer. It required to add mutex into struct snd_seq_client. See commit b3defb791b26ea06 ("ALSA: seq: Make ioctls race-free") and commit d15d662e89fc667b9 ("ALSA: seq: Fix racy pool initializations") This patch makes the API more safe. A custom constructor function and data are passed to klp_shadow_*alloc() functions instead of the sample data. Note that ctor_data are no longer a template for shadow->data. It might point to any data that might be necessary when the constructor is called. Also note that the constructor is called under klp_shadow_lock. It is an internal spin_lock that synchronizes alloc() vs. get() operations, see klp_shadow_get_or_alloc(). On one hand, this adds a risk of ABBA deadlocks. On the other hand, it allows to do some operations safely. For example, we could add the new structure into an existing list. This must be done only once when the structure is allocated. Reported-by: Nicolai Stange Signed-off-by: Petr Mladek Acked-by: Josh Poimboeuf Acked-by: Miroslav Benes Signed-off-by: Jiri Kosina --- include/linux/livepatch.h | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) (limited to 'include/linux/livepatch.h') diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h index 4754f01c1abb..7e084321b146 100644 --- a/include/linux/livepatch.h +++ b/include/linux/livepatch.h @@ -186,11 +186,17 @@ static inline bool klp_have_reliable_stack(void) IS_ENABLED(CONFIG_HAVE_RELIABLE_STACKTRACE); } +typedef int (*klp_shadow_ctor_t)(void *obj, + void *shadow_data, + void *ctor_data); + void *klp_shadow_get(void *obj, unsigned long id); -void *klp_shadow_alloc(void *obj, unsigned long id, void *data, - size_t size, gfp_t gfp_flags); -void *klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data, - size_t size, gfp_t gfp_flags); +void *klp_shadow_alloc(void *obj, unsigned long id, + size_t size, gfp_t gfp_flags, + klp_shadow_ctor_t ctor, void *ctor_data); +void *klp_shadow_get_or_alloc(void *obj, unsigned long id, + size_t size, gfp_t gfp_flags, + klp_shadow_ctor_t ctor, void *ctor_data); void klp_shadow_free(void *obj, unsigned long id); void klp_shadow_free_all(unsigned long id); -- cgit From 3b2c77d000fe9f7d02e9e726e00dccf9f92b256f Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Mon, 16 Apr 2018 13:36:47 +0200 Subject: livepatch: Allow to call a custom callback when freeing shadow variables We might need to do some actions before the shadow variable is freed. For example, we might need to remove it from a list or free some data that it points to. This is already possible now. The user can get the shadow variable by klp_shadow_get(), do the necessary actions, and then call klp_shadow_free(). This patch allows to do it a more elegant way. The user could implement the needed actions in a callback that is passed to klp_shadow_free() as a parameter. The callback usually does reverse operations to the constructor callback that can be called by klp_shadow_*alloc(). It is especially useful for klp_shadow_free_all(). There we need to do these extra actions for each found shadow variable with the given ID. Note that the memory used by the shadow variable itself is still released later by rcu callback. It is needed to protect internal structures that keep all shadow variables. But the destructor is called immediately. The shadow variable must not be access anyway after klp_shadow_free() is called. The user is responsible to protect this any suitable way. Be aware that the destructor is called under klp_shadow_lock. It is the same as for the contructor in klp_shadow_alloc(). Signed-off-by: Petr Mladek Acked-by: Josh Poimboeuf Acked-by: Miroslav Benes Signed-off-by: Jiri Kosina --- include/linux/livepatch.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'include/linux/livepatch.h') diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h index 7e084321b146..aec44b1d9582 100644 --- a/include/linux/livepatch.h +++ b/include/linux/livepatch.h @@ -189,6 +189,7 @@ static inline bool klp_have_reliable_stack(void) typedef int (*klp_shadow_ctor_t)(void *obj, void *shadow_data, void *ctor_data); +typedef void (*klp_shadow_dtor_t)(void *obj, void *shadow_data); void *klp_shadow_get(void *obj, unsigned long id); void *klp_shadow_alloc(void *obj, unsigned long id, @@ -197,8 +198,8 @@ void *klp_shadow_alloc(void *obj, unsigned long id, void *klp_shadow_get_or_alloc(void *obj, unsigned long id, size_t size, gfp_t gfp_flags, klp_shadow_ctor_t ctor, void *ctor_data); -void klp_shadow_free(void *obj, unsigned long id); -void klp_shadow_free_all(unsigned long id); +void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor); +void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor); #else /* !CONFIG_LIVEPATCH */ -- cgit