1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Here's a sample kernel module showing the use of fprobe to dump a 4 * stack trace and selected registers when kernel_clone() is called. 5 * 6 * For more information on theory of operation of kprobes, see 7 * Documentation/trace/kprobes.rst 8 * 9 * You will see the trace data in /var/log/messages and on the console 10 * 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 16 22 #define MAX_SYMBOL_LEN 4096 23 static struct fprobe sample_probe; 24 static unsigned long nhit; 25 26 static char symbol[MAX_SYMBOL_LEN] = "kernel_clone"; 27 module_param_string(symbol, symbol, sizeof(symbol), 0644); 28 MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern."); 29 30 static char nosymbol[MAX_SYMBOL_LEN] = ""; 31 module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644); 32 MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern."); 33 34 static bool stackdump = true; 35 module_param(stackdump, bool, 0644); 36 MODULE_PARM_DESC(stackdump, "Enable stackdump."); 37 38 static bool use_trace = false; 39 module_param(use_trace, bool, 0644); 40 MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging."); 41 42 static 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 51 static int sample_entry_handler(struct fprobe *fp, unsigned long ip, 52 struct pt_regs *regs, void *data) 53 { 54 if (use_trace) 55 /* 56 * This is just an example, no kernel code should call 57 * trace_printk() except when actively debugging. 58 */ 59 trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); 60 else 61 pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); 62 nhit++; 63 if (stackdump) 64 show_backtrace(); 65 return 0; 66 } 67 68 static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs, 69 void *data) 70 { 71 unsigned long rip = instruction_pointer(regs); 72 73 if (use_trace) 74 /* 75 * This is just an example, no kernel code should call 76 * trace_printk() except when actively debugging. 77 */ 78 trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", 79 (void *)ip, (void *)ip, (void *)rip, (void *)rip); 80 else 81 pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", 82 (void *)ip, (void *)ip, (void *)rip, (void *)rip); 83 nhit++; 84 if (stackdump) 85 show_backtrace(); 86 } 87 88 static int __init fprobe_init(void) 89 { 90 char *p, *symbuf = NULL; 91 const char **syms; 92 int ret, count, i; 93 94 sample_probe.entry_handler = sample_entry_handler; 95 sample_probe.exit_handler = sample_exit_handler; 96 97 if (strchr(symbol, '*')) { 98 /* filter based fprobe */ 99 ret = register_fprobe(&sample_probe, symbol, 100 nosymbol[0] == '\0' ? NULL : nosymbol); 101 goto out; 102 } else if (!strchr(symbol, ',')) { 103 symbuf = symbol; 104 ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1); 105 goto out; 106 } 107 108 /* Comma separated symbols */ 109 symbuf = kstrdup(symbol, GFP_KERNEL); 110 if (!symbuf) 111 return -ENOMEM; 112 p = symbuf; 113 count = 1; 114 while ((p = strchr(++p, ',')) != NULL) 115 count++; 116 117 pr_info("%d symbols found\n", count); 118 119 syms = kcalloc(count, sizeof(char *), GFP_KERNEL); 120 if (!syms) { 121 kfree(symbuf); 122 return -ENOMEM; 123 } 124 125 p = symbuf; 126 for (i = 0; i < count; i++) 127 syms[i] = strsep(&p, ","); 128 129 ret = register_fprobe_syms(&sample_probe, syms, count); 130 kfree(syms); 131 kfree(symbuf); 132 out: 133 if (ret < 0) 134 pr_err("register_fprobe failed, returned %d\n", ret); 135 else 136 pr_info("Planted fprobe at %s\n", symbol); 137 138 return ret; 139 } 140 141 static void __exit fprobe_exit(void) 142 { 143 unregister_fprobe(&sample_probe); 144 145 pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n", 146 symbol, nhit, sample_probe.nmissed); 147 } 148 149 module_init(fprobe_init) 150 module_exit(fprobe_exit) 151 MODULE_LICENSE("GPL"); 152