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_ARM64 42 pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx," 43 " pstate = 0x%lx\n", 44 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate); 45 #endif 46 #ifdef CONFIG_S390 47 pr_info("<%s> pre_handler: p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n", 48 p->symbol_name, p->addr, regs->psw.addr, regs->flags); 49 #endif 50 51 /* A dump_stack() here will give a stack backtrace */ 52 return 0; 53 } 54 55 /* kprobe post_handler: called after the probed instruction is executed */ 56 static void handler_post(struct kprobe *p, struct pt_regs *regs, 57 unsigned long flags) 58 { 59 #ifdef CONFIG_X86 60 pr_info("<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n", 61 p->symbol_name, p->addr, regs->flags); 62 #endif 63 #ifdef CONFIG_PPC 64 pr_info("<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n", 65 p->symbol_name, p->addr, regs->msr); 66 #endif 67 #ifdef CONFIG_MIPS 68 pr_info("<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n", 69 p->symbol_name, p->addr, regs->cp0_status); 70 #endif 71 #ifdef CONFIG_ARM64 72 pr_info("<%s> post_handler: p->addr = 0x%p, pstate = 0x%lx\n", 73 p->symbol_name, p->addr, (long)regs->pstate); 74 #endif 75 #ifdef CONFIG_S390 76 pr_info("<%s> pre_handler: p->addr, 0x%p, flags = 0x%lx\n", 77 p->symbol_name, p->addr, regs->flags); 78 #endif 79 } 80 81 /* 82 * fault_handler: this is called if an exception is generated for any 83 * instruction within the pre- or post-handler, or when Kprobes 84 * single-steps the probed instruction. 85 */ 86 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) 87 { 88 pr_info("fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr); 89 /* Return 0 because we don't handle the fault. */ 90 return 0; 91 } 92 93 static int __init kprobe_init(void) 94 { 95 int ret; 96 kp.pre_handler = handler_pre; 97 kp.post_handler = handler_post; 98 kp.fault_handler = handler_fault; 99 100 ret = register_kprobe(&kp); 101 if (ret < 0) { 102 pr_err("register_kprobe failed, returned %d\n", ret); 103 return ret; 104 } 105 pr_info("Planted kprobe at %p\n", kp.addr); 106 return 0; 107 } 108 109 static void __exit kprobe_exit(void) 110 { 111 unregister_kprobe(&kp); 112 pr_info("kprobe at %p unregistered\n", kp.addr); 113 } 114 115 module_init(kprobe_init) 116 module_exit(kprobe_exit) 117 MODULE_LICENSE("GPL"); 118