livepatch: Remove immediate feature
Immediate flag has been used to disable per-task consistency and patch
all tasks immediately. It could be useful if the patch doesn't change any
function or data semantics.
However, it causes problems on its own. The consistency problem is
currently broken with respect to immediate patches.
func a
patches 1i
2i
3
When the patch 3 is applied, only 2i function is checked (by stack
checking facility). There might be a task sleeping in 1i though. Such
task is migrated to 3, because we do not check 1i in
klp_check_stack_func() at all.
Coming atomic replace feature would be easier to implement and more
reliable without immediate.
Thus, remove immediate feature completely and save us from the problems.
Note that force feature has the similar problem. However it is
considered as a last resort. If used, administrator should not apply any
new live patches and should plan for reboot into an updated kernel.
The architectures would now need to provide HAVE_RELIABLE_STACKTRACE to
fully support livepatch.
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index be5bfa5..7c6631e 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -82,7 +82,6 @@
struct klp_func *func;
struct task_struct *g, *task;
unsigned int cpu;
- bool immediate_func = false;
pr_debug("'%s': completing %s transition\n",
klp_transition_patch->mod->name,
@@ -104,16 +103,9 @@
klp_synchronize_transition();
}
- if (klp_transition_patch->immediate)
- goto done;
-
- klp_for_each_object(klp_transition_patch, obj) {
- klp_for_each_func(obj, func) {
+ klp_for_each_object(klp_transition_patch, obj)
+ klp_for_each_func(obj, func)
func->transition = false;
- if (func->immediate)
- immediate_func = true;
- }
- }
/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
if (klp_target_state == KLP_PATCHED)
@@ -132,7 +124,6 @@
task->patch_state = KLP_UNDEFINED;
}
-done:
klp_for_each_object(klp_transition_patch, obj) {
if (!klp_is_object_loaded(obj))
continue;
@@ -146,16 +137,11 @@
klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
/*
- * See complementary comment in __klp_enable_patch() for why we
- * keep the module reference for immediate patches.
- *
- * klp_forced or immediate_func set implies unbounded increase of
- * module's ref count if the module is disabled/enabled in a loop.
+ * klp_forced set implies unbounded increase of module's ref count if
+ * the module is disabled/enabled in a loop.
*/
- if (!klp_forced && !klp_transition_patch->immediate &&
- !immediate_func && klp_target_state == KLP_UNPATCHED) {
+ if (!klp_forced && klp_target_state == KLP_UNPATCHED)
module_put(klp_transition_patch->mod);
- }
klp_target_state = KLP_UNDEFINED;
klp_transition_patch = NULL;
@@ -223,9 +209,6 @@
struct klp_ops *ops;
int i;
- if (func->immediate)
- return 0;
-
for (i = 0; i < trace->nr_entries; i++) {
address = trace->entries[i];
@@ -388,13 +371,6 @@
WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
/*
- * If the patch can be applied or reverted immediately, skip the
- * per-task transitions.
- */
- if (klp_transition_patch->immediate)
- goto success;
-
- /*
* Try to switch the tasks to the target patch state by walking their
* stacks and looking for any to-be-patched or to-be-unpatched
* functions. If such functions are found on a stack, or if the stack
@@ -437,7 +413,6 @@
return;
}
-success:
/* we're done, now cleanup the data structures */
klp_complete_transition();
}
@@ -458,13 +433,6 @@
klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
/*
- * If the patch can be applied or reverted immediately, skip the
- * per-task transitions.
- */
- if (klp_transition_patch->immediate)
- return;
-
- /*
* Mark all normal tasks as needing a patch state update. They'll
* switch either in klp_try_complete_transition() or as they exit the
* kernel.
@@ -514,13 +482,6 @@
klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
/*
- * If the patch can be applied or reverted immediately, skip the
- * per-task transitions.
- */
- if (patch->immediate)
- return;
-
- /*
* Initialize all tasks to the initial patch state to prepare them for
* switching to the target state.
*/