1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * NOTE: This example is works on x86 and powerpc. 4 * Here's a sample kernel module showing the use of kprobes to dump a 5 * stack trace and selected registers when kernel_clone() is called. 6 * 7 * For more information on theory of operation of kprobes, see 8 * Documentation/trace/kprobes.rst 9 * 10 * You will see the trace data in /var/log/messages and on the console 11 * whenever kernel_clone() is invoked to create a new process. 12 */ 13 14 #include <linux/kernel.h> 15 #include <linux/module.h> 16 #include <linux/kprobes.h> 17 18 #define MAX_SYMBOL_LEN 64 19 static char symbol[MAX_SYMBOL_LEN] = "kernel_clone"; 20 module_param_string(symbol, symbol, sizeof(symbol), 0644); 21 22 /* For each probe you need to allocate a kprobe structure */ 23 static struct kprobe kp = { 24 .symbol_name = symbol, 25 }; 26 27 /* kprobe pre_handler: called just before the probed instruction is executed */ 28 static int __kprobes handler_pre(struct kprobe *p, struct pt_regs *regs) 29 { 30 #ifdef CONFIG_X86 31 pr_info("<%s> pre_handler: p->addr = 0x%p, ip = %lx, flags = 0x%lx\n", 32 p->symbol_name, p->addr, regs->ip, regs->flags); 33 #endif 34 #ifdef CONFIG_PPC 35 pr_info("<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n", 36 p->symbol_name, p->addr, regs->nip, regs->msr); 37 #endif 38 #ifdef CONFIG_MIPS 39 pr_info("<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n", 40 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status); 41 #endif 42 #ifdef CONFIG_ARM64 43 pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx," 44 " pstate = 0x%lx\n", 45 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate); 46 #endif 47 #ifdef CONFIG_S390 48 pr_info("<%s> pre_handler: p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n", 49 p->symbol_name, p->addr, regs->psw.addr, regs->flags); 50 #endif 51 52 /* A dump_stack() here will give a stack backtrace */ 53 return 0; 54 } 55 56 /* kprobe post_handler: called after the probed instruction is executed */ 57 static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs, 58 unsigned long flags) 59 { 60 #ifdef CONFIG_X86 61 pr_info("<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n", 62 p->symbol_name, p->addr, regs->flags); 63 #endif 64 #ifdef CONFIG_PPC 65 pr_info("<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n", 66 p->symbol_name, p->addr, regs->msr); 67 #endif 68 #ifdef CONFIG_MIPS 69 pr_info("<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n", 70 p->symbol_name, p->addr, regs->cp0_status); 71 #endif 72 #ifdef CONFIG_ARM64 73 pr_info("<%s> post_handler: p->addr = 0x%p, pstate = 0x%lx\n", 74 p->symbol_name, p->addr, (long)regs->pstate); 75 #endif 76 #ifdef CONFIG_S390 77 pr_info("<%s> pre_handler: p->addr, 0x%p, flags = 0x%lx\n", 78 p->symbol_name, p->addr, regs->flags); 79 #endif 80 } 81 82 /* 83 * fault_handler: this is called if an exception is generated for any 84 * instruction within the pre- or post-handler, or when Kprobes 85 * single-steps the probed instruction. 86 */ 87 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) 88 { 89 pr_info("fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr); 90 /* Return 0 because we don't handle the fault. */ 91 return 0; 92 } 93 /* NOKPROBE_SYMBOL() is also available */ 94 NOKPROBE_SYMBOL(handler_fault); 95 96 static int __init kprobe_init(void) 97 { 98 int ret; 99 kp.pre_handler = handler_pre; 100 kp.post_handler = handler_post; 101 kp.fault_handler = handler_fault; 102 103 ret = register_kprobe(&kp); 104 if (ret < 0) { 105 pr_err("register_kprobe failed, returned %d\n", ret); 106 return ret; 107 } 108 pr_info("Planted kprobe at %p\n", kp.addr); 109 return 0; 110 } 111 112 static void __exit kprobe_exit(void) 113 { 114 unregister_kprobe(&kp); 115 pr_info("kprobe at %p unregistered\n", kp.addr); 116 } 117 118 module_init(kprobe_init) 119 module_exit(kprobe_exit) 120 MODULE_LICENSE("GPL"); 121