155 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/*3 * Here's a sample kernel module showing the use of fprobe to dump a4 * stack trace and selected registers when kernel_clone() is called.5 *6 * For more information on theory of operation of kprobes, see7 * Documentation/trace/kprobes.rst8 *9 * You will see the trace data in /var/log/messages and on the console10 * whenever kernel_clone() is invoked to create a new process.11 */12 13#define pr_fmt(fmt) "%s: " fmt, __func__14 15#include <linux/kernel.h>16#include <linux/module.h>17#include <linux/fprobe.h>18#include <linux/sched/debug.h>19#include <linux/slab.h>20 21#define BACKTRACE_DEPTH 1622#define MAX_SYMBOL_LEN 409623static struct fprobe sample_probe;24static unsigned long nhit;25 26static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";27module_param_string(symbol, symbol, sizeof(symbol), 0644);28MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern.");29 30static char nosymbol[MAX_SYMBOL_LEN] = "";31module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);32MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern.");33 34static bool stackdump = true;35module_param(stackdump, bool, 0644);36MODULE_PARM_DESC(stackdump, "Enable stackdump.");37 38static bool use_trace = false;39module_param(use_trace, bool, 0644);40MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging.");41 42static void show_backtrace(void)43{44 unsigned long stacks[BACKTRACE_DEPTH];45 unsigned int len;46 47 len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);48 stack_trace_print(stacks, len, 24);49}50 51static int sample_entry_handler(struct fprobe *fp, unsigned long ip,52 unsigned long ret_ip,53 struct pt_regs *regs, void *data)54{55 if (use_trace)56 /*57 * This is just an example, no kernel code should call58 * trace_printk() except when actively debugging.59 */60 trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);61 else62 pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);63 nhit++;64 if (stackdump)65 show_backtrace();66 return 0;67}68 69static void sample_exit_handler(struct fprobe *fp, unsigned long ip,70 unsigned long ret_ip, struct pt_regs *regs,71 void *data)72{73 unsigned long rip = ret_ip;74 75 if (use_trace)76 /*77 * This is just an example, no kernel code should call78 * trace_printk() except when actively debugging.79 */80 trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",81 (void *)ip, (void *)ip, (void *)rip, (void *)rip);82 else83 pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",84 (void *)ip, (void *)ip, (void *)rip, (void *)rip);85 nhit++;86 if (stackdump)87 show_backtrace();88}89 90static int __init fprobe_init(void)91{92 char *p, *symbuf = NULL;93 const char **syms;94 int ret, count, i;95 96 sample_probe.entry_handler = sample_entry_handler;97 sample_probe.exit_handler = sample_exit_handler;98 99 if (strchr(symbol, '*')) {100 /* filter based fprobe */101 ret = register_fprobe(&sample_probe, symbol,102 nosymbol[0] == '\0' ? NULL : nosymbol);103 goto out;104 } else if (!strchr(symbol, ',')) {105 symbuf = symbol;106 ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);107 goto out;108 }109 110 /* Comma separated symbols */111 symbuf = kstrdup(symbol, GFP_KERNEL);112 if (!symbuf)113 return -ENOMEM;114 p = symbuf;115 count = 1;116 while ((p = strchr(++p, ',')) != NULL)117 count++;118 119 pr_info("%d symbols found\n", count);120 121 syms = kcalloc(count, sizeof(char *), GFP_KERNEL);122 if (!syms) {123 kfree(symbuf);124 return -ENOMEM;125 }126 127 p = symbuf;128 for (i = 0; i < count; i++)129 syms[i] = strsep(&p, ",");130 131 ret = register_fprobe_syms(&sample_probe, syms, count);132 kfree(syms);133 kfree(symbuf);134out:135 if (ret < 0)136 pr_err("register_fprobe failed, returned %d\n", ret);137 else138 pr_info("Planted fprobe at %s\n", symbol);139 140 return ret;141}142 143static void __exit fprobe_exit(void)144{145 unregister_fprobe(&sample_probe);146 147 pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",148 symbol, nhit, sample_probe.nmissed);149}150 151module_init(fprobe_init)152module_exit(fprobe_exit)153MODULE_DESCRIPTION("sample kernel module showing the use of fprobe");154MODULE_LICENSE("GPL");155