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-rw-r--r--samples/fprobe/fprobe_example.c150
1 files changed, 150 insertions, 0 deletions
diff --git a/samples/fprobe/fprobe_example.c b/samples/fprobe/fprobe_example.c
new file mode 100644
index 000000000..dd794990a
--- /dev/null
+++ b/samples/fprobe/fprobe_example.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Here's a sample kernel module showing the use of fprobe to dump a
+ * stack trace and selected registers when kernel_clone() is called.
+ *
+ * For more information on theory of operation of kprobes, see
+ * Documentation/trace/kprobes.rst
+ *
+ * You will see the trace data in /var/log/messages and on the console
+ * whenever kernel_clone() is invoked to create a new process.
+ */
+
+#define pr_fmt(fmt) "%s: " fmt, __func__
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/fprobe.h>
+#include <linux/sched/debug.h>
+#include <linux/slab.h>
+
+#define BACKTRACE_DEPTH 16
+#define MAX_SYMBOL_LEN 4096
+static struct fprobe sample_probe;
+static unsigned long nhit;
+
+static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
+module_param_string(symbol, symbol, sizeof(symbol), 0644);
+MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern.");
+
+static char nosymbol[MAX_SYMBOL_LEN] = "";
+module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
+MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern.");
+
+static bool stackdump = true;
+module_param(stackdump, bool, 0644);
+MODULE_PARM_DESC(stackdump, "Enable stackdump.");
+
+static bool use_trace = false;
+module_param(use_trace, bool, 0644);
+MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging.");
+
+static void show_backtrace(void)
+{
+ unsigned long stacks[BACKTRACE_DEPTH];
+ unsigned int len;
+
+ len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);
+ stack_trace_print(stacks, len, 24);
+}
+
+static void sample_entry_handler(struct fprobe *fp, unsigned long ip,
+ struct pt_regs *regs, void *data)
+{
+ if (use_trace)
+ /*
+ * This is just an example, no kernel code should call
+ * trace_printk() except when actively debugging.
+ */
+ trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
+ else
+ pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
+ nhit++;
+ if (stackdump)
+ show_backtrace();
+}
+
+static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs,
+ void *data)
+{
+ unsigned long rip = instruction_pointer(regs);
+
+ if (use_trace)
+ /*
+ * This is just an example, no kernel code should call
+ * trace_printk() except when actively debugging.
+ */
+ trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
+ (void *)ip, (void *)ip, (void *)rip, (void *)rip);
+ else
+ pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
+ (void *)ip, (void *)ip, (void *)rip, (void *)rip);
+ nhit++;
+ if (stackdump)
+ show_backtrace();
+}
+
+static int __init fprobe_init(void)
+{
+ char *p, *symbuf = NULL;
+ const char **syms;
+ int ret, count, i;
+
+ sample_probe.entry_handler = sample_entry_handler;
+ sample_probe.exit_handler = sample_exit_handler;
+
+ if (strchr(symbol, '*')) {
+ /* filter based fprobe */
+ ret = register_fprobe(&sample_probe, symbol,
+ nosymbol[0] == '\0' ? NULL : nosymbol);
+ goto out;
+ } else if (!strchr(symbol, ',')) {
+ symbuf = symbol;
+ ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
+ goto out;
+ }
+
+ /* Comma separated symbols */
+ symbuf = kstrdup(symbol, GFP_KERNEL);
+ if (!symbuf)
+ return -ENOMEM;
+ p = symbuf;
+ count = 1;
+ while ((p = strchr(++p, ',')) != NULL)
+ count++;
+
+ pr_info("%d symbols found\n", count);
+
+ syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
+ if (!syms) {
+ kfree(symbuf);
+ return -ENOMEM;
+ }
+
+ p = symbuf;
+ for (i = 0; i < count; i++)
+ syms[i] = strsep(&p, ",");
+
+ ret = register_fprobe_syms(&sample_probe, syms, count);
+ kfree(syms);
+ kfree(symbuf);
+out:
+ if (ret < 0)
+ pr_err("register_fprobe failed, returned %d\n", ret);
+ else
+ pr_info("Planted fprobe at %s\n", symbol);
+
+ return ret;
+}
+
+static void __exit fprobe_exit(void)
+{
+ unregister_fprobe(&sample_probe);
+
+ pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
+ symbol, nhit, sample_probe.nmissed);
+}
+
+module_init(fprobe_init)
+module_exit(fprobe_exit)
+MODULE_LICENSE("GPL");