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 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 static char nosymbol[MAX_SYMBOL_LEN] = ""; 29 module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644); 30 static bool stackdump = true; 31 module_param(stackdump, bool, 0644); 32 static bool use_trace = false; 33 module_param(use_trace, bool, 0644); 34 35 static void show_backtrace(void) 36 { 37 unsigned long stacks[BACKTRACE_DEPTH]; 38 unsigned int len; 39 40 len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2); 41 stack_trace_print(stacks, len, 24); 42 } 43 44 static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs) 45 { 46 if (use_trace) 47 /* 48 * This is just an example, no kernel code should call 49 * trace_printk() except when actively debugging. 50 */ 51 trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); 52 else 53 pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); 54 nhit++; 55 if (stackdump) 56 show_backtrace(); 57 } 58 59 static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs) 60 { 61 unsigned long rip = instruction_pointer(regs); 62 63 if (use_trace) 64 /* 65 * This is just an example, no kernel code should call 66 * trace_printk() except when actively debugging. 67 */ 68 trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", 69 (void *)ip, (void *)ip, (void *)rip, (void *)rip); 70 else 71 pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", 72 (void *)ip, (void *)ip, (void *)rip, (void *)rip); 73 nhit++; 74 if (stackdump) 75 show_backtrace(); 76 } 77 78 static int __init fprobe_init(void) 79 { 80 char *p, *symbuf = NULL; 81 const char **syms; 82 int ret, count, i; 83 84 sample_probe.entry_handler = sample_entry_handler; 85 sample_probe.exit_handler = sample_exit_handler; 86 87 if (strchr(symbol, '*')) { 88 /* filter based fprobe */ 89 ret = register_fprobe(&sample_probe, symbol, 90 nosymbol[0] == '\0' ? NULL : nosymbol); 91 goto out; 92 } else if (!strchr(symbol, ',')) { 93 symbuf = symbol; 94 ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1); 95 goto out; 96 } 97 98 /* Comma separated symbols */ 99 symbuf = kstrdup(symbol, GFP_KERNEL); 100 if (!symbuf) 101 return -ENOMEM; 102 p = symbuf; 103 count = 1; 104 while ((p = strchr(++p, ',')) != NULL) 105 count++; 106 107 pr_info("%d symbols found\n", count); 108 109 syms = kcalloc(count, sizeof(char *), GFP_KERNEL); 110 if (!syms) { 111 kfree(symbuf); 112 return -ENOMEM; 113 } 114 115 p = symbuf; 116 for (i = 0; i < count; i++) 117 syms[i] = strsep(&p, ","); 118 119 ret = register_fprobe_syms(&sample_probe, syms, count); 120 kfree(syms); 121 kfree(symbuf); 122 out: 123 if (ret < 0) 124 pr_err("register_fprobe failed, returned %d\n", ret); 125 else 126 pr_info("Planted fprobe at %s\n", symbol); 127 128 return ret; 129 } 130 131 static void __exit fprobe_exit(void) 132 { 133 unregister_fprobe(&sample_probe); 134 135 pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n", 136 symbol, nhit, sample_probe.nmissed); 137 } 138 139 module_init(fprobe_init) 140 module_exit(fprobe_exit) 141 MODULE_LICENSE("GPL"); 142