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6ee64cc3 MH |
1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | /* | |
3 | * Here's a sample kernel module showing the use of fprobe to dump a | |
4 | * stack trace and selected registers when kernel_clone() is called. | |
5 | * | |
6 | * For more information on theory of operation of kprobes, see | |
7 | * Documentation/trace/kprobes.rst | |
8 | * | |
9 | * You will see the trace data in /var/log/messages and on the console | |
10 | * whenever kernel_clone() is invoked to create a new process. | |
11 | */ | |
12 | ||
13 | #define pr_fmt(fmt) "%s: " fmt, __func__ | |
14 | ||
15 | #include <linux/kernel.h> | |
16 | #include <linux/module.h> | |
17 | #include <linux/fprobe.h> | |
18 | #include <linux/sched/debug.h> | |
19 | #include <linux/slab.h> | |
20 | ||
21 | #define BACKTRACE_DEPTH 16 | |
22 | #define MAX_SYMBOL_LEN 4096 | |
e3655dfa | 23 | static struct fprobe sample_probe; |
c88dbbcd | 24 | static unsigned long nhit; |
6ee64cc3 MH |
25 | |
26 | static char symbol[MAX_SYMBOL_LEN] = "kernel_clone"; | |
27 | module_param_string(symbol, symbol, sizeof(symbol), 0644); | |
179a93f7 MHG |
28 | MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern."); |
29 | ||
6ee64cc3 MH |
30 | static char nosymbol[MAX_SYMBOL_LEN] = ""; |
31 | module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644); | |
179a93f7 MHG |
32 | MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern."); |
33 | ||
6ee64cc3 MH |
34 | static bool stackdump = true; |
35 | module_param(stackdump, bool, 0644); | |
179a93f7 MHG |
36 | MODULE_PARM_DESC(stackdump, "Enable stackdump."); |
37 | ||
c88dbbcd MHG |
38 | static bool use_trace = false; |
39 | module_param(use_trace, bool, 0644); | |
179a93f7 | 40 | MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging."); |
6ee64cc3 MH |
41 | |
42 | static void show_backtrace(void) | |
43 | { | |
44 | unsigned long stacks[BACKTRACE_DEPTH]; | |
45 | unsigned int len; | |
46 | ||
47 | len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2); | |
48 | stack_trace_print(stacks, len, 24); | |
49 | } | |
50 | ||
51 | static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs) | |
52 | { | |
c88dbbcd MHG |
53 | if (use_trace) |
54 | /* | |
55 | * This is just an example, no kernel code should call | |
56 | * trace_printk() except when actively debugging. | |
57 | */ | |
58 | trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); | |
59 | else | |
60 | pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); | |
61 | nhit++; | |
6ee64cc3 MH |
62 | if (stackdump) |
63 | show_backtrace(); | |
64 | } | |
65 | ||
66 | static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs) | |
67 | { | |
68 | unsigned long rip = instruction_pointer(regs); | |
69 | ||
c88dbbcd MHG |
70 | if (use_trace) |
71 | /* | |
72 | * This is just an example, no kernel code should call | |
73 | * trace_printk() except when actively debugging. | |
74 | */ | |
75 | trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", | |
76 | (void *)ip, (void *)ip, (void *)rip, (void *)rip); | |
77 | else | |
78 | pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", | |
79 | (void *)ip, (void *)ip, (void *)rip, (void *)rip); | |
80 | nhit++; | |
6ee64cc3 MH |
81 | if (stackdump) |
82 | show_backtrace(); | |
83 | } | |
84 | ||
85 | static int __init fprobe_init(void) | |
86 | { | |
87 | char *p, *symbuf = NULL; | |
88 | const char **syms; | |
89 | int ret, count, i; | |
90 | ||
91 | sample_probe.entry_handler = sample_entry_handler; | |
92 | sample_probe.exit_handler = sample_exit_handler; | |
93 | ||
94 | if (strchr(symbol, '*')) { | |
95 | /* filter based fprobe */ | |
96 | ret = register_fprobe(&sample_probe, symbol, | |
97 | nosymbol[0] == '\0' ? NULL : nosymbol); | |
98 | goto out; | |
99 | } else if (!strchr(symbol, ',')) { | |
100 | symbuf = symbol; | |
101 | ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1); | |
102 | goto out; | |
103 | } | |
104 | ||
105 | /* Comma separated symbols */ | |
106 | symbuf = kstrdup(symbol, GFP_KERNEL); | |
107 | if (!symbuf) | |
108 | return -ENOMEM; | |
109 | p = symbuf; | |
110 | count = 1; | |
111 | while ((p = strchr(++p, ',')) != NULL) | |
112 | count++; | |
113 | ||
114 | pr_info("%d symbols found\n", count); | |
115 | ||
116 | syms = kcalloc(count, sizeof(char *), GFP_KERNEL); | |
117 | if (!syms) { | |
118 | kfree(symbuf); | |
119 | return -ENOMEM; | |
120 | } | |
121 | ||
122 | p = symbuf; | |
123 | for (i = 0; i < count; i++) | |
124 | syms[i] = strsep(&p, ","); | |
125 | ||
126 | ret = register_fprobe_syms(&sample_probe, syms, count); | |
127 | kfree(syms); | |
128 | kfree(symbuf); | |
129 | out: | |
130 | if (ret < 0) | |
131 | pr_err("register_fprobe failed, returned %d\n", ret); | |
132 | else | |
133 | pr_info("Planted fprobe at %s\n", symbol); | |
134 | ||
135 | return ret; | |
136 | } | |
137 | ||
138 | static void __exit fprobe_exit(void) | |
139 | { | |
140 | unregister_fprobe(&sample_probe); | |
141 | ||
c88dbbcd MHG |
142 | pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n", |
143 | symbol, nhit, sample_probe.nmissed); | |
6ee64cc3 MH |
144 | } |
145 | ||
146 | module_init(fprobe_init) | |
147 | module_exit(fprobe_exit) | |
148 | MODULE_LICENSE("GPL"); |