[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 <pmla...@suse.com>
Suggested-by: Miroslav Benes <mbe...@suse.cz>
Suggested-by: Josh Poimboeuf <jpoim...@kernel.org>
Signed-off-by: Wardenjohn <zhangwar...@gmail.com>
---
 .../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-patch...@vger.kernel.org
+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