1 /* 2 * NOTE: This example is works on x86 and powerpc. 3 * Here's a sample kernel module showing the use of kprobes to dump a 4 * stack trace and selected registers when _do_fork() is called. 5 * 6 * For more information on theory of operation of kprobes, see 7 * Documentation/kprobes.txt 8 * 9 * You will see the trace data in /var/log/messages and on the console 10 * whenever _do_fork() is invoked to create a new process. 11 */ 12 13 #include <linux/kernel.h> 14 #include <linux/module.h> 15 #include <linux/kprobes.h> 16 17 #define MAX_SYMBOL_LEN 64 18 static char symbol[MAX_SYMBOL_LEN] = "_do_fork"; 19 module_param_string(symbol, symbol, sizeof(symbol), 0644); 20 21 /* For each probe you need to allocate a kprobe structure */ 22 static struct kprobe kp = { 23 .symbol_name = symbol, 24 }; 25 26 /* kprobe pre_handler: called just before the probed instruction is executed */ 27 static int handler_pre(struct kprobe *p, struct pt_regs *regs) 28 { 29 #ifdef CONFIG_X86 30 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, ip = %lx," 31 " flags = 0x%lx\n", 32 p->symbol_name, p->addr, regs->ip, regs->flags); 33 #endif 34 #ifdef CONFIG_PPC 35 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx," 36 " msr = 0x%lx\n", 37 p->symbol_name, p->addr, regs->nip, regs->msr); 38 #endif 39 #ifdef CONFIG_MIPS 40 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx," 41 " status = 0x%lx\n", 42 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status); 43 #endif 44 #ifdef CONFIG_TILEGX 45 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx," 46 " ex1 = 0x%lx\n", 47 p->symbol_name, p->addr, regs->pc, regs->ex1); 48 #endif 49 #ifdef CONFIG_ARM64 50 pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx," 51 " pstate = 0x%lx\n", 52 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate); 53 #endif 54 55 /* A dump_stack() here will give a stack backtrace */ 56 return 0; 57 } 58 59 /* kprobe post_handler: called after the probed instruction is executed */ 60 static void handler_post(struct kprobe *p, struct pt_regs *regs, 61 unsigned long flags) 62 { 63 #ifdef CONFIG_X86 64 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n", 65 p->symbol_name, p->addr, regs->flags); 66 #endif 67 #ifdef CONFIG_PPC 68 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n", 69 p->symbol_name, p->addr, regs->msr); 70 #endif 71 #ifdef CONFIG_MIPS 72 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n", 73 p->symbol_name, p->addr, regs->cp0_status); 74 #endif 75 #ifdef CONFIG_TILEGX 76 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, ex1 = 0x%lx\n", 77 p->symbol_name, p->addr, regs->ex1); 78 #endif 79 #ifdef CONFIG_ARM64 80 pr_info("<%s> post_handler: p->addr = 0x%p, pstate = 0x%lx\n", 81 p->symbol_name, p->addr, (long)regs->pstate); 82 #endif 83 } 84 85 /* 86 * fault_handler: this is called if an exception is generated for any 87 * instruction within the pre- or post-handler, or when Kprobes 88 * single-steps the probed instruction. 89 */ 90 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) 91 { 92 printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn", 93 p->addr, trapnr); 94 /* Return 0 because we don't handle the fault. */ 95 return 0; 96 } 97 98 static int __init kprobe_init(void) 99 { 100 int ret; 101 kp.pre_handler = handler_pre; 102 kp.post_handler = handler_post; 103 kp.fault_handler = handler_fault; 104 105 ret = register_kprobe(&kp); 106 if (ret < 0) { 107 printk(KERN_INFO "register_kprobe failed, returned %d\n", ret); 108 return ret; 109 } 110 printk(KERN_INFO "Planted kprobe at %p\n", kp.addr); 111 return 0; 112 } 113 114 static void __exit kprobe_exit(void) 115 { 116 unregister_kprobe(&kp); 117 printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr); 118 } 119 120 module_init(kprobe_init) 121 module_exit(kprobe_exit) 122 MODULE_LICENSE("GPL"); 123