[RFC PATCH 3/4] livepatch: Add "replaceable" attribute to klp_patch

[Yafang Shao <laoar.shao@gmail.com>]

Add a new replaceable attribute to allow the coexistence of both
atomic-replace and non-atomic-replace livepatches. If replaceable is set to
0, the livepatch will not be replaced by a subsequent atomic-replace
operation.

This is a preparatory patch for following changes.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/linux/livepatch.h |  2 ++
 kernel/livepatch/core.c   | 44 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index ba9e3988c07c..d88a6966e5f2 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -124,6 +124,7 @@ struct klp_state {
  * @objs:	object entries for kernel objects to be patched
  * @states:	system states that can get modified
  * @replace:	replace all actively used patches
+ * @replaceable:	whether this patch can be replaced or not
  * @list:	list node for global list of actively used patches
  * @kobj:	kobject for sysfs resources
  * @obj_list:	dynamic list of the object entries
@@ -138,6 +139,7 @@ struct klp_patch {
 	struct klp_object *objs;
 	struct klp_state *states;
 	bool replace;
+	bool replaceable;
 
 	/* internal */
 	struct list_head list;
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 28d15ba58a26..04f9e84f114f 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -351,6 +351,7 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
  * /sys/kernel/livepatch/<patch>/transition
  * /sys/kernel/livepatch/<patch>/force
  * /sys/kernel/livepatch/<patch>/replace
+ * /sys/kernel/livepatch/<patch>/replaceable
  * /sys/kernel/livepatch/<patch>/stack_order
  * /sys/kernel/livepatch/<patch>/<object>
  * /sys/kernel/livepatch/<patch>/<object>/patched
@@ -478,17 +479,60 @@ static ssize_t stack_order_show(struct kobject *kobj,
 	return sysfs_emit(buf, "%d\n", stack_order);
 }
 
+static ssize_t replaceable_store(struct kobject *kobj, struct kobj_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct klp_patch *patch;
+	bool replaceable;
+	int ret;
+
+	ret = kstrtobool(buf, &replaceable);
+	if (ret)
+		return ret;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+
+	mutex_lock(&klp_mutex);
+
+	if (patch->replaceable == replaceable)
+		goto out;
+
+	if (patch == klp_transition_patch) {
+		ret = -EAGAIN;
+		goto out;
+	}
+
+	patch->replaceable = replaceable;
+
+out:
+	mutex_unlock(&klp_mutex);
+
+	if (ret)
+		return ret;
+	return count;
+}
+static ssize_t replaceable_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	struct klp_patch *patch;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	return sysfs_emit(buf, "%d\n", patch->replaceable);
+}
+
 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
 static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
 static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
 static struct kobj_attribute replace_kobj_attr = __ATTR_RO(replace);
 static struct kobj_attribute stack_order_kobj_attr = __ATTR_RO(stack_order);
+static struct kobj_attribute replaceable_kobj_attr = __ATTR_RW(replaceable);
 static struct attribute *klp_patch_attrs[] = {
 	&enabled_kobj_attr.attr,
 	&transition_kobj_attr.attr,
 	&force_kobj_attr.attr,
 	&replace_kobj_attr.attr,
 	&stack_order_kobj_attr.attr,
+	&replaceable_kobj_attr.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(klp_patch);
-- 
2.47.3