[PATCH V3 1/1] livepatch: Add "stack_order" sysfs attribute

[Wardenjohn]

Add "stack_order" sysfs attribute which holds the order in which a live
patch module was loaded into the system. A user can then determine an
active live patched version of a function.

cat /sys/kernel/livepatch/livepatch_1/stack_order -> 1

means that livepatch_1 is the first live patch applied

cat /sys/kernel/livepatch/livepatch_module/stack_order -> N

means that livepatch_module is the Nth live patch applied

Suggested-by: Petr Mladek <pmladek@xxxxxxxx>
Suggested-by: Miroslav Benes <mbenes@xxxxxxx>
Suggested-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Wardenjohn <zhangwarden@xxxxxxxxx>
---
 .../ABI/testing/sysfs-kernel-livepatch        |  8 ++++++
 kernel/livepatch/core.c                       | 25 +++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
index a5df9b4910dc..2a60b49aa9a5 100644
--- a/Documentation/ABI/testing/sysfs-kernel-livepatch
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -47,6 +47,14 @@ Description:
 		disabled when the feature is used. See
 		Documentation/livepatch/livepatch.rst for more information.
 
+What:           /sys/kernel/livepatch/<patch>/stack_order
+Date:           Sep 2024
+KernelVersion:  6.12.0
+Contact:        live-patching@xxxxxxxxxxxxxxx
+Description:
+		This attribute holds the stack order of a livepatch module applied
+		to the running system.
+
 What:		/sys/kernel/livepatch/<patch>/<object>
 Date:		Nov 2014
 KernelVersion:	3.19.0
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index ecbc9b6aba3a..30ab3668c59e 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -346,6 +346,7 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
  * /sys/kernel/livepatch/<patch>/enabled
  * /sys/kernel/livepatch/<patch>/transition
  * /sys/kernel/livepatch/<patch>/force
+ * /sys/kernel/livepatch/<patch>/stack_order
  * /sys/kernel/livepatch/<patch>/<object>
  * /sys/kernel/livepatch/<patch>/<object>/patched
  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
@@ -443,13 +444,37 @@ static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
 	return count;
 }
 
+static ssize_t stack_order_show(struct kobject *kobj,
+				struct kobj_attribute *attr, char *buf)
+{
+	struct klp_patch *patch, *this_patch;
+	int stack_order = 0;
+
+	this_patch = container_of(kobj, struct klp_patch, kobj);
+
+	mutex_lock(&klp_mutex);
+
+	klp_for_each_patch(patch) {
+		stack_order++;
+		if (patch == this_patch)
+			break;
+	}
+
+	mutex_unlock(&klp_mutex);
+
+	return sysfs_emit(buf, "%d\n", stack_order);
+}
+
+
 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 stack_order_kobj_attr = __ATTR_RO(stack_order);
 static struct attribute *klp_patch_attrs[] = {
 	&enabled_kobj_attr.attr,
 	&transition_kobj_attr.attr,
 	&force_kobj_attr.attr,
+	&stack_order_kobj_attr.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(klp_patch);
-- 
2.18.2