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authorLinus Torvalds <torvalds@linux-foundation.org>2015-03-18 10:46:39 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-03-18 10:46:39 -0700
commitda11508eb0b00740c7b05290d80d3f38618af4e8 (patch)
treee970834609500f9fb7ba4ce288b7bc387ab101a0 /kernel
parente63c733d03070d4d3aaf3a29775b42fa9ab95bbf (diff)
parent8cb2c2dc472775479a1a7e78180955f6f1cb0b0a (diff)
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Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching
Pull livepatching fix from Jiri Kosina: - fix for potential race with module loading, from Petr Mladek. The race is very unlikely to be seen in real world and has been found by code inspection, but should be fixed for 4.0 anyway. * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching: livepatch: Fix subtle race with coming and going modules
Diffstat (limited to 'kernel')
-rw-r--r--kernel/livepatch/core.c30
1 files changed, 26 insertions, 4 deletions
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 01ca08804f51..3f9f1d6b4c2e 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -89,16 +89,28 @@ static bool klp_is_object_loaded(struct klp_object *obj)
/* sets obj->mod if object is not vmlinux and module is found */
static void klp_find_object_module(struct klp_object *obj)
{
+ struct module *mod;
+
if (!klp_is_module(obj))
return;
mutex_lock(&module_mutex);
/*
- * We don't need to take a reference on the module here because we have
- * the klp_mutex, which is also taken by the module notifier. This
- * prevents any module from unloading until we release the klp_mutex.
+ * We do not want to block removal of patched modules and therefore
+ * we do not take a reference here. The patches are removed by
+ * a going module handler instead.
+ */
+ mod = find_module(obj->name);
+ /*
+ * Do not mess work of the module coming and going notifiers.
+ * Note that the patch might still be needed before the going handler
+ * is called. Module functions can be called even in the GOING state
+ * until mod->exit() finishes. This is especially important for
+ * patches that modify semantic of the functions.
*/
- obj->mod = find_module(obj->name);
+ if (mod && mod->klp_alive)
+ obj->mod = mod;
+
mutex_unlock(&module_mutex);
}
@@ -767,6 +779,7 @@ static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
return -EINVAL;
obj->state = KLP_DISABLED;
+ obj->mod = NULL;
klp_find_object_module(obj);
@@ -961,6 +974,15 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
mutex_lock(&klp_mutex);
+ /*
+ * Each module has to know that the notifier has been called.
+ * We never know what module will get patched by a new patch.
+ */
+ if (action == MODULE_STATE_COMING)
+ mod->klp_alive = true;
+ else /* MODULE_STATE_GOING */
+ mod->klp_alive = false;
+
list_for_each_entry(patch, &klp_patches, list) {
for (obj = patch->objs; obj->funcs; obj++) {
if (!klp_is_module(obj) || strcmp(obj->name, mod->name))