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 pr_info("<%s> pre_handler: p->addr = 0x%p, ip = %lx, flags = 0x%lx\n", 31 p->symbol_name, p->addr, regs->ip, regs->flags); 32 #endif 33 #ifdef CONFIG_PPC 34 pr_info("<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n", 35 p->symbol_name, p->addr, regs->nip, regs->msr); 36 #endif 37 #ifdef CONFIG_MIPS 38 pr_info("<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n", 39 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status); 40 #endif 41 #ifdef CONFIG_TILEGX 42 pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx, ex1 = 0x%lx\n", 43 p->symbol_name, p->addr, regs->pc, regs->ex1); 44 #endif 45 #ifdef CONFIG_ARM64 46 pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx," 47 " pstate = 0x%lx\n", 48 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate); 49 #endif 50 #ifdef CONFIG_S390 51 pr_info("<%s> pre_handler: p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n", 52 p->symbol_name, p->addr, regs->psw.addr, regs->flags); 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 pr_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 pr_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 pr_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 pr_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 #ifdef CONFIG_S390 84 pr_info("<%s> pre_handler: p->addr, 0x%p, flags = 0x%lx\n", 85 p->symbol_name, p->addr, regs->flags); 86 #endif 87 } 88 89 /* 90 * fault_handler: this is called if an exception is generated for any 91 * instruction within the pre- or post-handler, or when Kprobes 92 * single-steps the probed instruction. 93 */ 94 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) 95 { 96 pr_info("fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr); 97 /* Return 0 because we don't handle the fault. */ 98 return 0; 99 } 100 101 static int __init kprobe_init(void) 102 { 103 int ret; 104 kp.pre_handler = handler_pre; 105 kp.post_handler = handler_post; 106 kp.fault_handler = handler_fault; 107 108 ret = register_kprobe(&kp); 109 if (ret < 0) { 110 pr_err("register_kprobe failed, returned %d\n", ret); 111 return ret; 112 } 113 pr_info("Planted kprobe at %p\n", kp.addr); 114 return 0; 115 } 116 117 static void __exit kprobe_exit(void) 118 { 119 unregister_kprobe(&kp); 120 pr_info("kprobe at %p unregistered\n", kp.addr); 121 } 122 123 module_init(kprobe_init) 124 module_exit(kprobe_exit) 125 MODULE_LICENSE("GPL"); 126