From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Add a new livepatch sample in samples/livepatch/ to make use of symbols
that must be post-processed to enable load-time relocation resolution.
As the new sample is to be used as an example, it is annotated with
KLP_RELOC_SYMBOL macro.
The livepatch sample updates the function cmdline_proc_show to print the
string referenced by the symbol saved_command_line appended by the
string "livepatch=1".
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Lukas Hruska <lhruska@xxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
---
samples/livepatch/Makefile | 1 +
samples/livepatch/livepatch-extern-symbol.c | 84 +++++++++++++++++++++
2 files changed, 85 insertions(+)
create mode 100644 samples/livepatch/livepatch-extern-symbol.c
diff --git a/samples/livepatch/Makefile b/samples/livepatch/Makefile
index 9f853eeb6140..5cc81d5db17c 100644
--- a/samples/livepatch/Makefile
+++ b/samples/livepatch/Makefile
@@ -6,3 +6,4 @@ obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-shadow-fix2.o
obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-callbacks-demo.o
obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-callbacks-mod.o
obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-callbacks-busymod.o
+obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-extern-symbol.o
diff --git a/samples/livepatch/livepatch-extern-symbol.c b/samples/livepatch/livepatch-extern-symbol.c
new file mode 100644
index 000000000000..276a43d157b4
--- /dev/null
+++ b/samples/livepatch/livepatch-extern-symbol.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
+ */
+
+/*
+ * livepatch-extern-symbol.c - Kernel Live Patching Sample Module
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/livepatch.h>
+
+/*
+ * This (dumb) live patch overrides the function that prints the
+ * kernel boot cmdline when /proc/cmdline is read.
+ *
+ * This livepatch uses the symbol saved_command_line whose relocation
+ * must be resolved during load time. To enable that, this module
+ * must be post-processed by a tool called klp-convert, which embeds
+ * information to be used by the loader to solve the relocation.
+ *
+ * The module is annotated with KLP_RELOC_SYMBOL macros.
+ * These annotations are used by klp-convert to infer that the symbol
+ * saved_command_line is in the object vmlinux.
+ *
+ * Example:
+ *
+ * $ cat /proc/cmdline
+ * <your cmdline>
+ *
+ * $ insmod livepatch-sample.ko
+ * $ cat /proc/cmdline
+ * <your cmdline> livepatch=1
+ *
+ * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
+ * $ cat /proc/cmdline
+ * <your cmdline>
+ */
+
+extern char *saved_command_line \
+ KLP_RELOC_SYMBOL(vmlinux, vmlinux, saved_command_line);
+
+#include <linux/seq_file.h>
+static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "%s livepatch=1\n", saved_command_line);
+ return 0;
+}
+
+static struct klp_func funcs[] = {
+ {
+ .old_name = "cmdline_proc_show",
+ .new_func = livepatch_cmdline_proc_show,
+ }, { }
+};
+
+static struct klp_object objs[] = {
+ {
+ /* name being NULL means vmlinux */
+ .funcs = funcs,
+ }, { }
+};
+
+static struct klp_patch patch = {
+ .mod = THIS_MODULE,
+ .objs = objs,
+};
+
+static int livepatch_init(void)
+{
+ return klp_enable_patch(&patch);
+}
+
+static void livepatch_exit(void)
+{
+}
+
+module_init(livepatch_init);
+module_exit(livepatch_exit);
+MODULE_LICENSE("GPL");
+MODULE_INFO(livepatch, "Y");
--
2.46.0
