[PATCH v13 05/12] livepatch: Refuse to unload only livepatches available during a forced transition

Petr Mladek
2018-10-15T12:37:37Z

module_put() is currently never called in klp_complete_transition() when
klp_force is set. As a result, we might keep the reference count even when
klp_enable_patch() fails and klp_cancel_transition() is called.

This might make an assumption that a module might get blocked in some
strange init state. Fortunately, it is not the case. The reference count
is ignored when mod->init fails and erroneous modules are always removed.

Anyway, this might make some confusion. Instead, this patch moves
the global klp_forced flag into struct klp_patch. As a result,
we block only modules that might still be in use after a forced
transition. Newly loaded livepatches might be eventually completely
removed later.

It is not a big deal. But the code is at least consistent with
the reality.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
include/linux/livepatch.h | 2 ++
kernel/livepatch/core.c | 4 +++-
kernel/livepatch/core.h | 1 +
kernel/livepatch/transition.c | 10 +++++-----
4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 1163742b27c0..77fce7d385df 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -138,6 +138,7 @@ struct klp_object {
* @list: list node for global list of registered patches
* @kobj: kobject for sysfs resources
* @enabled: the patch is enabled (but operation may be incomplete)
+ * @forced: was involved in a forced transition
* @finish: for waiting till it is safe to remove the patch module
*/
struct klp_patch {
@@ -149,6 +150,7 @@ struct klp_patch {
struct list_head list;
struct kobject kobj;
bool enabled;
+ bool forced;
struct completion finish;
};

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 17cb974522d0..f38637326ac2 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -45,7 +45,8 @@
*/
DEFINE_MUTEX(klp_mutex);

-static LIST_HEAD(klp_patches);
+/* Registered patches */
+LIST_HEAD(klp_patches);

static struct kobject *klp_root_kobj;

@@ -647,6 +648,7 @@ static int klp_init_patch(struct klp_patch *patch)
mutex_lock(&klp_mutex);

patch->enabled = false;
+ patch->forced = false;
INIT_LIST_HEAD(&patch->list);
init_completion(&patch->finish);

diff --git a/kernel/livepatch/core.h b/kernel/livepatch/core.h
index 48a83d4364cf..d0cb5390e247 100644
--- a/kernel/livepatch/core.h
+++ b/kernel/livepatch/core.h
@@ -5,6 +5,7 @@
#include <linux/livepatch.h>

extern struct mutex klp_mutex;
+extern struct list_head klp_patches;

static inline bool klp_is_object_loaded(struct klp_object *obj)
{
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 982a2e4c6120..30a28634c88c 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -33,8 +33,6 @@ struct klp_patch *klp_transition_patch;

static int klp_target_state = KLP_UNDEFINED;

-static bool klp_forced = false;
-
/*
* This work can be performed periodically to finish patching or unpatching any
* "straggler" tasks which failed to transition in the first attempt.
@@ -137,10 +135,10 @@ static void klp_complete_transition(void)
klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

/*
- * klp_forced set implies unbounded increase of module's ref count if
+ * patch->forced set implies unbounded increase of module's ref count if
* the module is disabled/enabled in a loop.
*/
- if (!klp_forced && klp_target_state == KLP_UNPATCHED)
+ if (!klp_transition_patch->forced && klp_target_state == KLP_UNPATCHED)
module_put(klp_transition_patch->mod);

klp_target_state = KLP_UNDEFINED;
@@ -620,6 +618,7 @@ void klp_send_signals(void)
*/
void klp_force_transition(void)
{
+ struct klp_patch *patch;
struct task_struct *g, *task;
unsigned int cpu;

@@ -633,5 +632,6 @@ void klp_force_transition(void)
for_each_possible_cpu(cpu)
klp_update_patch_state(idle_task(cpu));

- klp_forced = true;
+ list_for_each_entry(patch, &klp_patches, list)
+ patch->forced = true;
}
--
2.13.7