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
52extern struct bug_entry __start___bug_table[], __stop___bug_table[];
53
54static 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 */
65static LIST_HEAD(module_bug_list);
66
67static 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
84void 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(new: &mod->bug_list, head: &module_bug_list);
111}
112
113void module_bug_cleanup(struct module *mod)
114{
115 list_del_rcu(entry: &mod->bug_list);
116}
117
118#else
119
120static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
121{
122 return NULL;
123}
124#endif
125
126void 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
142static 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
165struct 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__diag_push();
177__diag_ignore(GCC, all, "-Wsuggest-attribute=format",
178 "Not a valid __printf() conversion candidate.");
179static void __warn_printf(const char *fmt, struct pt_regs *regs)
180{
181 if (!fmt)
182 return;
183
184#ifdef HAVE_ARCH_BUG_FORMAT_ARGS
185 if (regs) {
186 struct arch_va_list _args;
187 va_list *args = __warn_args(args: &_args, regs);
188
189 if (args) {
190 vprintk(fmt, args: *args);
191 return;
192 }
193 }
194#endif
195
196 printk("%s", fmt);
197}
198__diag_pop();
199
200static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long bugaddr, struct pt_regs *regs)
201{
202 bool warning, once, done, no_cut, has_args;
203 const char *file, *fmt;
204 unsigned line;
205
206 if (!bug) {
207 if (!is_valid_bugaddr(addr: bugaddr))
208 return BUG_TRAP_TYPE_NONE;
209
210 bug = find_bug(bugaddr);
211 if (!bug)
212 return BUG_TRAP_TYPE_NONE;
213 }
214
215 disable_trace_on_warning();
216
217 bug_get_file_line(bug, file: &file, line: &line);
218 fmt = bug_get_format(bug);
219
220 warning = bug->flags & BUGFLAG_WARNING;
221 once = bug->flags & BUGFLAG_ONCE;
222 done = bug->flags & BUGFLAG_DONE;
223 no_cut = bug->flags & BUGFLAG_NO_CUT_HERE;
224 has_args = bug->flags & BUGFLAG_ARGS;
225
226 if (warning && once) {
227 if (done)
228 return BUG_TRAP_TYPE_WARN;
229
230 /*
231 * Since this is the only store, concurrency is not an issue.
232 */
233 bug->flags |= BUGFLAG_DONE;
234 }
235
236 /*
237 * BUG() and WARN_ON() families don't print a custom debug message
238 * before triggering the exception handler, so we must add the
239 * "cut here" line now. WARN() issues its own "cut here" before the
240 * extra debugging message it writes before triggering the handler.
241 */
242 if (!no_cut) {
243 printk(KERN_DEFAULT CUT_HERE);
244 __warn_printf(fmt, regs: has_args ? regs : NULL);
245 }
246
247 if (warning) {
248 /* this is a WARN_ON rather than BUG/BUG_ON */
249 __warn(file, line, caller: (void *)bugaddr, BUG_GET_TAINT(bug), regs,
250 NULL);
251 return BUG_TRAP_TYPE_WARN;
252 }
253
254 if (file)
255 pr_crit("kernel BUG at %s:%u!\n", file, line);
256 else
257 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
258 (void *)bugaddr);
259
260 return BUG_TRAP_TYPE_BUG;
261}
262
263enum bug_trap_type report_bug_entry(struct bug_entry *bug, struct pt_regs *regs)
264{
265 enum bug_trap_type ret;
266 bool rcu = false;
267
268 rcu = warn_rcu_enter();
269 ret = __report_bug(bug, bugaddr: bug_addr(bug), regs);
270 warn_rcu_exit(rcu);
271
272 return ret;
273}
274
275enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
276{
277 enum bug_trap_type ret;
278 bool rcu = false;
279
280 rcu = warn_rcu_enter();
281 ret = __report_bug(NULL, bugaddr, regs);
282 warn_rcu_exit(rcu);
283
284 return ret;
285}
286
287static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
288{
289 struct bug_entry *bug;
290
291 for (bug = start; bug < end; bug++)
292 bug->flags &= ~BUGFLAG_DONE;
293}
294
295void generic_bug_clear_once(void)
296{
297#ifdef CONFIG_MODULES
298 struct module *mod;
299
300 scoped_guard(rcu) {
301 list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
302 clear_once_table(start: mod->bug_table,
303 end: mod->bug_table + mod->num_bugs);
304 }
305#endif
306
307 clear_once_table(start: __start___bug_table, end: __stop___bug_table);
308}
309

source code of linux/lib/bug.c