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Subject[PATCH 3/3] livepatch: add shadow variable sample program
Date
Modify the sample livepatch to demonstrate the shadow variable API.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
samples/livepatch/livepatch-sample.c | 39 +++++++++++++++++++++++++++++++++++-
1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
index 84795223f15f..e0236750cefb 100644
--- a/samples/livepatch/livepatch-sample.c
+++ b/samples/livepatch/livepatch-sample.c
@@ -25,26 +25,57 @@

/*
* This (dumb) live patch overrides the function that prints the
- * kernel boot cmdline when /proc/cmdline is read.
+ * kernel boot cmdline when /proc/cmdline is read. It also
+ * demonstrates a contrived shadow-variable usage.
*
* Example:
*
* $ cat /proc/cmdline
* <your cmdline>
+ * current=<current task pointer> count=<shadow variable counter>
*
* $ insmod livepatch-sample.ko
* $ cat /proc/cmdline
* this has been live patched
+ * current=ffff8800331c9540 count=1
+ * $ cat /proc/cmdline
+ * this has been live patched
+ * current=ffff8800331c9540 count=2
*
* $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
* $ cat /proc/cmdline
* <your cmdline>
*/

+static LIST_HEAD(shadow_list);
+
+struct task_ctr {
+ struct list_head list;
+ int count;
+};
+
#include <linux/seq_file.h>
+#include <linux/slab.h>
static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
{
+ struct task_ctr *nd;
+
+ nd = klp_shadow_get(current, "task_ctr");
+ if (!nd) {
+ nd = kzalloc(sizeof(*nd), GFP_KERNEL);
+ if (nd) {
+ list_add(&nd->list, &shadow_list);
+ klp_shadow_attach(current, "task_ctr", GFP_KERNEL, nd);
+ }
+ }
+
seq_printf(m, "%s\n", "this has been live patched");
+
+ if (nd) {
+ nd->count++;
+ seq_printf(m, "current=%p count=%d\n", current, nd->count);
+ }
+
return 0;
}

@@ -99,6 +130,12 @@ static int livepatch_init(void)

static void livepatch_exit(void)
{
+ struct task_ctr *nd, *tmp;
+
+ list_for_each_entry_safe(nd, tmp, &shadow_list, list) {
+ list_del(&nd->list);
+ kfree(nd);
+ }
WARN_ON(klp_unregister_patch(&patch));
}

--
1.8.3.1
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