1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 Generic support for BUG()
4
5 This respects the following config options:
6
7 CONFIG_BUG - emit BUG traps. Nothing happens without this.
8 CONFIG_GENERIC_BUG - enable this code.
9 CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit relative pointers for bug_addr and file
10 CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG
11
12 CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
13 (though they're generally always on).
14
15 CONFIG_GENERIC_BUG is set by each architecture using this code.
16
17 To use this, your architecture must:
18
19 1. Set up the config options:
20 - Enable CONFIG_GENERIC_BUG if CONFIG_BUG
21
22 2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)
23 - Define HAVE_ARCH_BUG
24 - Implement BUG() to generate a faulting instruction
25 - NOTE: struct bug_entry does not have "file" or "line" entries
26 when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
27 the values accordingly.
28
29 3. Implement the trap
30 - In the illegal instruction trap handler (typically), verify
31 that the fault was in kernel mode, and call report_bug()
32 - report_bug() will return whether it was a false alarm, a warning,
33 or an actual bug.
34 - You must implement the is_valid_bugaddr(bugaddr) callback which
35 returns true if the eip is a real kernel address, and it points
36 to the expected BUG trap instruction.
37
38 Jeremy Fitzhardinge <jeremy@goop.org> 2006
39 */
40
41 #define pr_fmt(fmt) fmt
42
43 #include <linux/list.h>
44 #include <linux/module.h>
45 #include <linux/kernel.h>
46 #include <linux/bug.h>
47 #include <linux/sched.h>
48 #include <linux/rculist.h>
49 #include <linux/ftrace.h>
50 #include <linux/context_tracking.h>
51
52 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
53
bug_addr(const struct bug_entry * bug)54 static inline unsigned long bug_addr(const struct bug_entry *bug)
55 {
56 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
57 return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;
58 #else
59 return bug->bug_addr;
60 #endif
61 }
62
63 #ifdef CONFIG_MODULES
64 /* Updates are protected by module mutex */
65 static LIST_HEAD(module_bug_list);
66
module_find_bug(unsigned long bugaddr)67 static struct bug_entry *module_find_bug(unsigned long bugaddr)
68 {
69 struct bug_entry *bug;
70 struct module *mod;
71
72 guard(rcu)();
73 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
74 unsigned i;
75
76 bug = mod->bug_table;
77 for (i = 0; i < mod->num_bugs; ++i, ++bug)
78 if (bugaddr == bug_addr(bug))
79 return bug;
80 }
81 return NULL;
82 }
83
module_bug_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)84 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
85 struct module *mod)
86 {
87 char *secstrings;
88 unsigned int i;
89
90 mod->bug_table = NULL;
91 mod->num_bugs = 0;
92
93 /* Find the __bug_table section, if present */
94 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
95 for (i = 1; i < hdr->e_shnum; i++) {
96 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
97 continue;
98 mod->bug_table = (void *) sechdrs[i].sh_addr;
99 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
100 break;
101 }
102
103 /*
104 * Strictly speaking this should have a spinlock to protect against
105 * traversals, but since we only traverse on BUG()s, a spinlock
106 * could potentially lead to deadlock and thus be counter-productive.
107 * Thus, this uses RCU to safely manipulate the bug list, since BUG
108 * must run in non-interruptive state.
109 */
110 list_add_rcu(&mod->bug_list, &module_bug_list);
111 }
112
module_bug_cleanup(struct module * mod)113 void module_bug_cleanup(struct module *mod)
114 {
115 list_del_rcu(&mod->bug_list);
116 }
117
118 #else
119
module_find_bug(unsigned long bugaddr)120 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
121 {
122 return NULL;
123 }
124 #endif
125
bug_get_file_line(struct bug_entry * bug,const char ** file,unsigned int * line)126 void bug_get_file_line(struct bug_entry *bug, const char **file,
127 unsigned int *line)
128 {
129 #ifdef CONFIG_DEBUG_BUGVERBOSE
130 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
131 *file = (const char *)&bug->file_disp + bug->file_disp;
132 #else
133 *file = bug->file;
134 #endif
135 *line = bug->line;
136 #else
137 *file = NULL;
138 *line = 0;
139 #endif
140 }
141
bug_get_format(struct bug_entry * bug)142 static const char *bug_get_format(struct bug_entry *bug)
143 {
144 const char *format = NULL;
145 #ifdef HAVE_ARCH_BUG_FORMAT
146 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
147 /*
148 * Allow an architecture to:
149 * - relative encode NULL (difficult vs KASLR);
150 * - use a literal 0 (there are no valid objects inside
151 * the __bug_table itself to refer to after all);
152 * - use an empty string.
153 */
154 if (bug->format_disp)
155 format = (const char *)&bug->format_disp + bug->format_disp;
156 if (format && format[0] == '\0')
157 format = NULL;
158 #else
159 format = bug->format;
160 #endif
161 #endif
162 return format;
163 }
164
find_bug(unsigned long bugaddr)165 struct bug_entry *find_bug(unsigned long bugaddr)
166 {
167 struct bug_entry *bug;
168
169 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
170 if (bugaddr == bug_addr(bug))
171 return bug;
172
173 return module_find_bug(bugaddr);
174 }
175
176 static __printf(1, 0)
__warn_printf(const char * fmt,struct pt_regs * regs)177 void __warn_printf(const char *fmt, struct pt_regs *regs)
178 {
179 if (!fmt)
180 return;
181
182 #ifdef HAVE_ARCH_BUG_FORMAT_ARGS
183 if (regs) {
184 struct arch_va_list _args;
185 va_list *args = __warn_args(&_args, regs);
186
187 if (args) {
188 vprintk(fmt, *args);
189 return;
190 }
191 }
192 #endif
193
194 printk("%s", fmt);
195 }
196
__report_bug(struct bug_entry * bug,unsigned long bugaddr,struct pt_regs * regs)197 static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long bugaddr, struct pt_regs *regs)
198 {
199 bool warning, once, done, no_cut, has_args;
200 const char *file, *fmt;
201 unsigned line;
202
203 if (!bug) {
204 if (!is_valid_bugaddr(bugaddr))
205 return BUG_TRAP_TYPE_NONE;
206
207 bug = find_bug(bugaddr);
208 if (!bug)
209 return BUG_TRAP_TYPE_NONE;
210 }
211
212 disable_trace_on_warning();
213
214 bug_get_file_line(bug, &file, &line);
215 fmt = bug_get_format(bug);
216
217 warning = bug->flags & BUGFLAG_WARNING;
218 once = bug->flags & BUGFLAG_ONCE;
219 done = bug->flags & BUGFLAG_DONE;
220 no_cut = bug->flags & BUGFLAG_NO_CUT_HERE;
221 has_args = bug->flags & BUGFLAG_ARGS;
222
223 if (warning && once) {
224 if (done)
225 return BUG_TRAP_TYPE_WARN;
226
227 /*
228 * Since this is the only store, concurrency is not an issue.
229 */
230 bug->flags |= BUGFLAG_DONE;
231 }
232
233 /*
234 * BUG() and WARN_ON() families don't print a custom debug message
235 * before triggering the exception handler, so we must add the
236 * "cut here" line now. WARN() issues its own "cut here" before the
237 * extra debugging message it writes before triggering the handler.
238 */
239 if (!no_cut) {
240 printk(KERN_DEFAULT CUT_HERE);
241 __warn_printf(fmt, has_args ? regs : NULL);
242 }
243
244 if (warning) {
245 /* this is a WARN_ON rather than BUG/BUG_ON */
246 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
247 NULL);
248 return BUG_TRAP_TYPE_WARN;
249 }
250
251 if (file)
252 pr_crit("kernel BUG at %s:%u!\n", file, line);
253 else
254 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
255 (void *)bugaddr);
256
257 return BUG_TRAP_TYPE_BUG;
258 }
259
report_bug_entry(struct bug_entry * bug,struct pt_regs * regs)260 enum bug_trap_type report_bug_entry(struct bug_entry *bug, struct pt_regs *regs)
261 {
262 enum bug_trap_type ret;
263 bool rcu = false;
264
265 rcu = warn_rcu_enter();
266 ret = __report_bug(bug, bug_addr(bug), regs);
267 warn_rcu_exit(rcu);
268
269 return ret;
270 }
271
report_bug(unsigned long bugaddr,struct pt_regs * regs)272 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
273 {
274 enum bug_trap_type ret;
275 bool rcu = false;
276
277 rcu = warn_rcu_enter();
278 ret = __report_bug(NULL, bugaddr, regs);
279 warn_rcu_exit(rcu);
280
281 return ret;
282 }
283
clear_once_table(struct bug_entry * start,struct bug_entry * end)284 static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
285 {
286 struct bug_entry *bug;
287
288 for (bug = start; bug < end; bug++)
289 bug->flags &= ~BUGFLAG_DONE;
290 }
291
generic_bug_clear_once(void)292 void generic_bug_clear_once(void)
293 {
294 #ifdef CONFIG_MODULES
295 struct module *mod;
296
297 scoped_guard(rcu) {
298 list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
299 clear_once_table(mod->bug_table,
300 mod->bug_table + mod->num_bugs);
301 }
302 #endif
303
304 clear_once_table(__start___bug_table, __stop___bug_table);
305 }
306