[PATCH 3/3] livepatch: Add a sysctl livepatch_mode for atomic replace

[Jason Baron]

Introduce a sysctl knob such that by default livepatch is not in
'atomic replace' mode. A '0' in /proc/sys/kernel/livepatch_mode means the
current default mode, while a '1' means do atomic replace.

Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
Cc: Jiri Kosina <jikos@xxxxxxxxxx>
Cc: Miroslav Benes <mbenes@xxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
---
 include/linux/livepatch.h |  8 ++++++++
 kernel/livepatch/core.c   |  5 +++++
 kernel/sysctl.c           | 12 ++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 6fd7222..08e760a 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -35,6 +35,14 @@
 #define KLP_UNPATCHED	 0
 #define KLP_PATCHED	 1
 
+/* livepatch mode */
+
+extern int sysctl_livepatch_mode;
+enum {
+	LIVEPATCH_MODE_DEFAULT,
+	LIVEPATCH_MODE_REPLACE,
+};
+
 /**
  * struct klp_func - function structure for live patching
  * @old_name:	name of the function to be patched
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index bf353da..b1df5c4 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -49,6 +49,8 @@ static LIST_HEAD(klp_patches);
 
 static struct kobject *klp_root_kobj;
 
+int sysctl_livepatch_mode;
+
 static bool klp_is_module(struct klp_object *obj)
 {
 	return obj->name;
@@ -643,6 +645,9 @@ static int klp_init_patch_no_ops(struct klp_patch *patch)
 	if (patch->list.prev == &klp_patches)
 		return 0;
 
+	if (sysctl_livepatch_mode != LIVEPATCH_MODE_REPLACE)
+		return 0;
+
 	prev_patch = list_prev_entry(patch, list);
 	klp_for_each_object(prev_patch, prev_obj, &prev_o_iter) {
 		if (!klp_is_object_loaded(prev_obj))
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4dfba1a..3a0a1f6 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -67,6 +67,7 @@
 #include <linux/kexec.h>
 #include <linux/bpf.h>
 #include <linux/mount.h>
+#include <linux/livepatch.h>
 
 #include <linux/uaccess.h>
 #include <asm/processor.h>
@@ -1203,6 +1204,17 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &one,
 	},
 #endif
+#ifdef CONFIG_LIVEPATCH
+	{
+		.procname	= "livepatch_mode",
+		.data		= &sysctl_livepatch_mode,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
+#endif
 	{ }
 };
 
-- 
2.6.1