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authorPetr Mladek <pmladek@suse.com>2018-04-16 13:36:46 +0200
committerJiri Kosina <jkosina@suse.cz>2018-04-17 13:42:48 +0200
commite91c2518a5d22a07642f35d85f39001ad379dae4 (patch)
tree3a794a957564ce90514894263e995fbd27649a8c /include/linux
parente1c70f32386c4984ed8ca1a7aedb9bbff9ed3414 (diff)
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 <nstange@suse.de> Signed-off-by: Petr Mladek <pmladek@suse.com> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/livepatch.h14
1 files changed, 10 insertions, 4 deletions
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);