xref: /openbmc/linux/kernel/trace/trace_printk.c (revision 4e4f6e33)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * trace binary printk
4  *
5  * Copyright (C) 2008 Lai Jiangshan <laijs@cn.fujitsu.com>
6  *
7  */
8 #include <linux/seq_file.h>
9 #include <linux/security.h>
10 #include <linux/uaccess.h>
11 #include <linux/kernel.h>
12 #include <linux/ftrace.h>
13 #include <linux/string.h>
14 #include <linux/module.h>
15 #include <linux/mutex.h>
16 #include <linux/ctype.h>
17 #include <linux/list.h>
18 #include <linux/slab.h>
19 
20 #include "trace.h"
21 
22 #ifdef CONFIG_MODULES
23 
24 /*
25  * modules trace_printk()'s formats are autosaved in struct trace_bprintk_fmt
26  * which are queued on trace_bprintk_fmt_list.
27  */
28 static LIST_HEAD(trace_bprintk_fmt_list);
29 
30 /* serialize accesses to trace_bprintk_fmt_list */
31 static DEFINE_MUTEX(btrace_mutex);
32 
33 struct trace_bprintk_fmt {
34 	struct list_head list;
35 	const char *fmt;
36 };
37 
lookup_format(const char * fmt)38 static inline struct trace_bprintk_fmt *lookup_format(const char *fmt)
39 {
40 	struct trace_bprintk_fmt *pos;
41 
42 	if (!fmt)
43 		return ERR_PTR(-EINVAL);
44 
45 	list_for_each_entry(pos, &trace_bprintk_fmt_list, list) {
46 		if (!strcmp(pos->fmt, fmt))
47 			return pos;
48 	}
49 	return NULL;
50 }
51 
52 static
hold_module_trace_bprintk_format(const char ** start,const char ** end)53 void hold_module_trace_bprintk_format(const char **start, const char **end)
54 {
55 	const char **iter;
56 	char *fmt;
57 
58 	/* allocate the trace_printk per cpu buffers */
59 	if (start != end)
60 		trace_printk_init_buffers();
61 
62 	mutex_lock(&btrace_mutex);
63 	for (iter = start; iter < end; iter++) {
64 		struct trace_bprintk_fmt *tb_fmt = lookup_format(*iter);
65 		if (tb_fmt) {
66 			if (!IS_ERR(tb_fmt))
67 				*iter = tb_fmt->fmt;
68 			continue;
69 		}
70 
71 		fmt = NULL;
72 		tb_fmt = kmalloc(sizeof(*tb_fmt), GFP_KERNEL);
73 		if (tb_fmt) {
74 			fmt = kmalloc(strlen(*iter) + 1, GFP_KERNEL);
75 			if (fmt) {
76 				list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
77 				strcpy(fmt, *iter);
78 				tb_fmt->fmt = fmt;
79 			} else
80 				kfree(tb_fmt);
81 		}
82 		*iter = fmt;
83 
84 	}
85 	mutex_unlock(&btrace_mutex);
86 }
87 
module_trace_bprintk_format_notify(struct notifier_block * self,unsigned long val,void * data)88 static int module_trace_bprintk_format_notify(struct notifier_block *self,
89 		unsigned long val, void *data)
90 {
91 	struct module *mod = data;
92 	if (mod->num_trace_bprintk_fmt) {
93 		const char **start = mod->trace_bprintk_fmt_start;
94 		const char **end = start + mod->num_trace_bprintk_fmt;
95 
96 		if (val == MODULE_STATE_COMING)
97 			hold_module_trace_bprintk_format(start, end);
98 	}
99 	return NOTIFY_OK;
100 }
101 
102 /*
103  * The debugfs/tracing/printk_formats file maps the addresses with
104  * the ASCII formats that are used in the bprintk events in the
105  * buffer. For userspace tools to be able to decode the events from
106  * the buffer, they need to be able to map the address with the format.
107  *
108  * The addresses of the bprintk formats are in their own section
109  * __trace_printk_fmt. But for modules we copy them into a link list.
110  * The code to print the formats and their addresses passes around the
111  * address of the fmt string. If the fmt address passed into the seq
112  * functions is within the kernel core __trace_printk_fmt section, then
113  * it simply uses the next pointer in the list.
114  *
115  * When the fmt pointer is outside the kernel core __trace_printk_fmt
116  * section, then we need to read the link list pointers. The trick is
117  * we pass the address of the string to the seq function just like
118  * we do for the kernel core formats. To get back the structure that
119  * holds the format, we simply use container_of() and then go to the
120  * next format in the list.
121  */
122 static const char **
find_next_mod_format(int start_index,void * v,const char ** fmt,loff_t * pos)123 find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
124 {
125 	struct trace_bprintk_fmt *mod_fmt;
126 
127 	if (list_empty(&trace_bprintk_fmt_list))
128 		return NULL;
129 
130 	/*
131 	 * v will point to the address of the fmt record from t_next
132 	 * v will be NULL from t_start.
133 	 * If this is the first pointer or called from start
134 	 * then we need to walk the list.
135 	 */
136 	if (!v || start_index == *pos) {
137 		struct trace_bprintk_fmt *p;
138 
139 		/* search the module list */
140 		list_for_each_entry(p, &trace_bprintk_fmt_list, list) {
141 			if (start_index == *pos)
142 				return &p->fmt;
143 			start_index++;
144 		}
145 		/* pos > index */
146 		return NULL;
147 	}
148 
149 	/*
150 	 * v points to the address of the fmt field in the mod list
151 	 * structure that holds the module print format.
152 	 */
153 	mod_fmt = container_of(v, typeof(*mod_fmt), fmt);
154 	if (mod_fmt->list.next == &trace_bprintk_fmt_list)
155 		return NULL;
156 
157 	mod_fmt = container_of(mod_fmt->list.next, typeof(*mod_fmt), list);
158 
159 	return &mod_fmt->fmt;
160 }
161 
format_mod_start(void)162 static void format_mod_start(void)
163 {
164 	mutex_lock(&btrace_mutex);
165 }
166 
format_mod_stop(void)167 static void format_mod_stop(void)
168 {
169 	mutex_unlock(&btrace_mutex);
170 }
171 
172 #else /* !CONFIG_MODULES */
173 __init static int
module_trace_bprintk_format_notify(struct notifier_block * self,unsigned long val,void * data)174 module_trace_bprintk_format_notify(struct notifier_block *self,
175 		unsigned long val, void *data)
176 {
177 	return NOTIFY_OK;
178 }
179 static inline const char **
find_next_mod_format(int start_index,void * v,const char ** fmt,loff_t * pos)180 find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
181 {
182 	return NULL;
183 }
format_mod_start(void)184 static inline void format_mod_start(void) { }
format_mod_stop(void)185 static inline void format_mod_stop(void) { }
186 #endif /* CONFIG_MODULES */
187 
188 static bool __read_mostly trace_printk_enabled = true;
189 
trace_printk_control(bool enabled)190 void trace_printk_control(bool enabled)
191 {
192 	trace_printk_enabled = enabled;
193 }
194 
195 __initdata_or_module static
196 struct notifier_block module_trace_bprintk_format_nb = {
197 	.notifier_call = module_trace_bprintk_format_notify,
198 };
199 
__trace_bprintk(unsigned long ip,const char * fmt,...)200 int __trace_bprintk(unsigned long ip, const char *fmt, ...)
201 {
202 	int ret;
203 	va_list ap;
204 
205 	if (unlikely(!fmt))
206 		return 0;
207 
208 	if (!trace_printk_enabled)
209 		return 0;
210 
211 	va_start(ap, fmt);
212 	ret = trace_vbprintk(ip, fmt, ap);
213 	va_end(ap);
214 	return ret;
215 }
216 EXPORT_SYMBOL_GPL(__trace_bprintk);
217 
__ftrace_vbprintk(unsigned long ip,const char * fmt,va_list ap)218 int __ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap)
219 {
220 	if (unlikely(!fmt))
221 		return 0;
222 
223 	if (!trace_printk_enabled)
224 		return 0;
225 
226 	return trace_vbprintk(ip, fmt, ap);
227 }
228 EXPORT_SYMBOL_GPL(__ftrace_vbprintk);
229 
__trace_printk(unsigned long ip,const char * fmt,...)230 int __trace_printk(unsigned long ip, const char *fmt, ...)
231 {
232 	int ret;
233 	va_list ap;
234 
235 	if (!trace_printk_enabled)
236 		return 0;
237 
238 	va_start(ap, fmt);
239 	ret = trace_vprintk(ip, fmt, ap);
240 	va_end(ap);
241 	return ret;
242 }
243 EXPORT_SYMBOL_GPL(__trace_printk);
244 
__ftrace_vprintk(unsigned long ip,const char * fmt,va_list ap)245 int __ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap)
246 {
247 	if (!trace_printk_enabled)
248 		return 0;
249 
250 	return trace_vprintk(ip, fmt, ap);
251 }
252 EXPORT_SYMBOL_GPL(__ftrace_vprintk);
253 
trace_is_tracepoint_string(const char * str)254 bool trace_is_tracepoint_string(const char *str)
255 {
256 	const char **ptr = __start___tracepoint_str;
257 
258 	for (ptr = __start___tracepoint_str; ptr < __stop___tracepoint_str; ptr++) {
259 		if (str == *ptr)
260 			return true;
261 	}
262 	return false;
263 }
264 
find_next(void * v,loff_t * pos)265 static const char **find_next(void *v, loff_t *pos)
266 {
267 	const char **fmt = v;
268 	int start_index;
269 	int last_index;
270 
271 	start_index = __stop___trace_bprintk_fmt - __start___trace_bprintk_fmt;
272 
273 	if (*pos < start_index)
274 		return __start___trace_bprintk_fmt + *pos;
275 
276 	/*
277 	 * The __tracepoint_str section is treated the same as the
278 	 * __trace_printk_fmt section. The difference is that the
279 	 * __trace_printk_fmt section should only be used by trace_printk()
280 	 * in a debugging environment, as if anything exists in that section
281 	 * the trace_prink() helper buffers are allocated, which would just
282 	 * waste space in a production environment.
283 	 *
284 	 * The __tracepoint_str sections on the other hand are used by
285 	 * tracepoints which need to map pointers to their strings to
286 	 * the ASCII text for userspace.
287 	 */
288 	last_index = start_index;
289 	start_index = __stop___tracepoint_str - __start___tracepoint_str;
290 
291 	if (*pos < last_index + start_index)
292 		return __start___tracepoint_str + (*pos - last_index);
293 
294 	start_index += last_index;
295 	return find_next_mod_format(start_index, v, fmt, pos);
296 }
297 
298 static void *
t_start(struct seq_file * m,loff_t * pos)299 t_start(struct seq_file *m, loff_t *pos)
300 {
301 	format_mod_start();
302 	return find_next(NULL, pos);
303 }
304 
t_next(struct seq_file * m,void * v,loff_t * pos)305 static void *t_next(struct seq_file *m, void * v, loff_t *pos)
306 {
307 	(*pos)++;
308 	return find_next(v, pos);
309 }
310 
t_show(struct seq_file * m,void * v)311 static int t_show(struct seq_file *m, void *v)
312 {
313 	const char **fmt = v;
314 	const char *str = *fmt;
315 	int i;
316 
317 	if (!*fmt)
318 		return 0;
319 
320 	seq_printf(m, "0x%lx : \"", *(unsigned long *)fmt);
321 
322 	/*
323 	 * Tabs and new lines need to be converted.
324 	 */
325 	for (i = 0; str[i]; i++) {
326 		switch (str[i]) {
327 		case '\n':
328 			seq_puts(m, "\\n");
329 			break;
330 		case '\t':
331 			seq_puts(m, "\\t");
332 			break;
333 		case '\\':
334 			seq_putc(m, '\\');
335 			break;
336 		case '"':
337 			seq_puts(m, "\\\"");
338 			break;
339 		default:
340 			seq_putc(m, str[i]);
341 		}
342 	}
343 	seq_puts(m, "\"\n");
344 
345 	return 0;
346 }
347 
t_stop(struct seq_file * m,void * p)348 static void t_stop(struct seq_file *m, void *p)
349 {
350 	format_mod_stop();
351 }
352 
353 static const struct seq_operations show_format_seq_ops = {
354 	.start = t_start,
355 	.next = t_next,
356 	.show = t_show,
357 	.stop = t_stop,
358 };
359 
360 static int
ftrace_formats_open(struct inode * inode,struct file * file)361 ftrace_formats_open(struct inode *inode, struct file *file)
362 {
363 	int ret;
364 
365 	ret = security_locked_down(LOCKDOWN_TRACEFS);
366 	if (ret)
367 		return ret;
368 
369 	return seq_open(file, &show_format_seq_ops);
370 }
371 
372 static const struct file_operations ftrace_formats_fops = {
373 	.open = ftrace_formats_open,
374 	.read = seq_read,
375 	.llseek = seq_lseek,
376 	.release = seq_release,
377 };
378 
init_trace_printk_function_export(void)379 static __init int init_trace_printk_function_export(void)
380 {
381 	int ret;
382 
383 	ret = tracing_init_dentry();
384 	if (ret)
385 		return 0;
386 
387 	trace_create_file("printk_formats", TRACE_MODE_READ, NULL,
388 				    NULL, &ftrace_formats_fops);
389 
390 	return 0;
391 }
392 
393 fs_initcall(init_trace_printk_function_export);
394 
init_trace_printk(void)395 static __init int init_trace_printk(void)
396 {
397 	return register_module_notifier(&module_trace_bprintk_format_nb);
398 }
399 
400 early_initcall(init_trace_printk);
401