livepatch: add (un)patch callbacks

Provide livepatch modules a klp_object (un)patching notification
mechanism.  Pre and post-(un)patch callbacks allow livepatch modules to
setup or synchronize changes that would be difficult to support in only
patched-or-unpatched code contexts.

Callbacks can be registered for target module or vmlinux klp_objects,
but each implementation is klp_object specific.

  - Pre-(un)patch callbacks run before any (un)patching transition
    starts.

  - Post-(un)patch callbacks run once an object has been (un)patched and
    the klp_patch fully transitioned to its target state.

Example use cases include modification of global data and registration
of newly available services/handlers.

See Documentation/livepatch/callbacks.txt for details and
samples/livepatch/ for examples.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 41 insertions, 10 deletions

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index b9628e43c78f..cafb5a84417d 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -54,11 +54,6 @@ static bool klp_is_module(struct klp_object *obj)
         return obj->name;
 }
 
-static bool klp_is_object_loaded(struct klp_object *obj)
-{
-        return !obj->name || obj->mod;
-}
-
 /* sets obj->mod if object is not vmlinux and module is found */
 static void klp_find_object_module(struct klp_object *obj)
 {
@@ -285,6 +280,8 @@ static int klp_write_object_relocations(struct module *pmod,
 
 static int __klp_disable_patch(struct klp_patch *patch)
 {
+        struct klp_object *obj;
+
         if (klp_transition_patch)
                 return -EBUSY;
 
@@ -295,6 +292,10 @@ static int __klp_disable_patch(struct klp_patch *patch)
 
         klp_init_transition(patch, KLP_UNPATCHED);
 
+        klp_for_each_object(patch, obj)
+                if (patch->enabled && obj->patched)
+                        klp_pre_unpatch_callback(obj);
+
         /*
          * Enforce the order of the func->transition writes in
          * klp_init_transition() and the TIF_PATCH_PENDING writes in
@@ -388,13 +389,18 @@ static int __klp_enable_patch(struct klp_patch *patch)
                 if (!klp_is_object_loaded(obj))
                         continue;
 
-                ret = klp_patch_object(obj);
+                ret = klp_pre_patch_callback(obj);
                 if (ret) {
-                        pr_warn("failed to enable patch '%s'\n",
-                                patch->mod->name);
+                        pr_warn("pre-patch callback failed for object '%s'\n",
+                                klp_is_module(obj) ? obj->name : "vmlinux");
+                        goto err;
+                }
 
-                        klp_cancel_transition();
-                        return ret;
+                ret = klp_patch_object(obj);
+                if (ret) {
+                        pr_warn("failed to patch object '%s'\n",
+                                klp_is_module(obj) ? obj->name : "vmlinux");
+                        goto err;
                 }
         }
 
@@ -403,6 +409,11 @@ static int __klp_enable_patch(struct klp_patch *patch)
         patch->enabled = true;
 
         return 0;
+err:
+        pr_warn("failed to enable patch '%s'\n", patch->mod->name);
+
+        klp_cancel_transition();
+        return ret;
 }
 
 /**
@@ -871,13 +882,27 @@ int klp_module_coming(struct module *mod)
                         pr_notice("applying patch '%s' to loading module '%s'\n",
                                   patch->mod->name, obj->mod->name);
 
+                        ret = klp_pre_patch_callback(obj);
+                        if (ret) {
+                                pr_warn("pre-patch callback failed for object '%s'\n",
+                                        obj->name);
+                                goto err;
+                        }
+
                         ret = klp_patch_object(obj);
                         if (ret) {
                                 pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
                                         patch->mod->name, obj->mod->name, ret);
+
+                                if (patch != klp_transition_patch)
+                                        klp_post_unpatch_callback(obj);
+
                                 goto err;
                         }
 
+                        if (patch != klp_transition_patch)
+                                klp_post_patch_callback(obj);
+
                         break;
                 }
         }
@@ -927,9 +952,15 @@ void klp_module_going(struct module *mod)
                          * is in transition.
                          */
                         if (patch->enabled || patch == klp_transition_patch) {
+
+                                if (patch != klp_transition_patch)
+                                        klp_pre_unpatch_callback(obj);
+
                                 pr_notice("reverting patch '%s' on unloading module '%s'\n",
                                           patch->mod->name, obj->mod->name);
                                 klp_unpatch_object(obj);
+
+                                klp_post_unpatch_callback(obj);
                         }
 
                         klp_free_object_loaded(obj);