[PATCH V4 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        |  9 +++++++
 kernel/livepatch/core.c                       | 24 +++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch 
b/Documentation/ABI/testing/sysfs-kernel-livepatch
index 3735d868013d..73e40d02345e 100644
--- a/Documentation/ABI/testing/sysfs-kernel-livepatch
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -55,6 +55,15 @@ Description:
                An attribute which indicates whether the patch supports
                atomic-replace.
 
+What:          /sys/kernel/livepatch/<patch>/stack_order
+Date:          Oct 2024
+KernelVersion: 6.13.0
+Description:
+               This attribute specifies the sequence in which live patch module
+               are applied to the system. If multiple live patches modify the 
same
+               function, the implementation with the biggest 'stack_order' 
number
+               is used, unless a transition is currently in progress.
+
 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 3c21c31796db..0cd39954d5a1 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -347,6 +347,7 @@ 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>/stack_order
  * /sys/kernel/livepatch/<patch>/<object>
  * /sys/kernel/livepatch/<patch>/<object>/patched
  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
@@ -452,15 +453,38 @@ static ssize_t replace_show(struct kobject *kobj,
        return sysfs_emit(buf, "%d\n", patch->replace);
 }
 
+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 replace_kobj_attr = __ATTR_RO(replace);
+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,
        &replace_kobj_attr.attr,
+       &stack_order_kobj_attr.attr,
        NULL
 };
 ATTRIBUTE_GROUPS(klp_patch);
-- 
2.18.2