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 _do_fork() is called.
6 *
7 * For more information on theory of operation of kprobes, see
8 * Documentation/kprobes.txt
9 *
10 * You will see the trace data in /var/log/messages and on the console
11 * whenever _do_fork() 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] = "_do_fork";
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 */
handler_pre(struct kprobe * p,struct pt_regs * regs)28 static int 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 */
handler_post(struct kprobe * p,struct pt_regs * regs,unsigned long flags)57 static void 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 */
handler_fault(struct kprobe * p,struct pt_regs * regs,int trapnr)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
kprobe_init(void)94 static int __init kprobe_init(void)
95 {
96 int ret;
97 kp.pre_handler = handler_pre;
98 kp.post_handler = handler_post;
99 kp.fault_handler = handler_fault;
100
101 ret = register_kprobe(&kp);
102 if (ret < 0) {
103 pr_err("register_kprobe failed, returned %d\n", ret);
104 return ret;
105 }
106 pr_info("Planted kprobe at %p\n", kp.addr);
107 return 0;
108 }
109
kprobe_exit(void)110 static void __exit kprobe_exit(void)
111 {
112 unregister_kprobe(&kp);
113 pr_info("kprobe at %p unregistered\n", kp.addr);
114 }
115
116 module_init(kprobe_init)
117 module_exit(kprobe_exit)
118 MODULE_LICENSE("GPL");
119