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
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
67 static struct bug_entry *module_find_bug(unsigned long bugaddr)
68 {
69 struct module *mod;
70 struct bug_entry *bug = NULL;
71
72 rcu_read_lock_sched();
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 goto out;
80 }
81 bug = NULL;
82 out:
83 rcu_read_unlock_sched();
84
85 return bug;
86 }
87
88 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
89 struct module *mod)
90 {
91 char *secstrings;
92 unsigned int i;
93
94 mod->bug_table = NULL;
95 mod->num_bugs = 0;
96
97 /* Find the __bug_table section, if present */
98 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
99 for (i = 1; i < hdr->e_shnum; i++) {
100 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
101 continue;
102 mod->bug_table = (void *) sechdrs[i].sh_addr;
103 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
104 break;
105 }
106
107 /*
108 * Strictly speaking this should have a spinlock to protect against
109 * traversals, but since we only traverse on BUG()s, a spinlock
110 * could potentially lead to deadlock and thus be counter-productive.
111 * Thus, this uses RCU to safely manipulate the bug list, since BUG
112 * must run in non-interruptive state.
113 */
114 list_add_rcu(&mod->bug_list, &module_bug_list);
115 }
116
117 void module_bug_cleanup(struct module *mod)
118 {
119 list_del_rcu(&mod->bug_list);
120 }
121
122 #else
123
124 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
125 {
126 return NULL;
127 }
128 #endif
129
130 void bug_get_file_line(struct bug_entry *bug, const char **file,
131 unsigned int *line)
132 {
133 #ifdef CONFIG_DEBUG_BUGVERBOSE
134 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
135 *file = (const char *)&bug->file_disp + bug->file_disp;
136 #else
137 *file = bug->file;
138 #endif
139 *line = bug->line;
140 #else
141 *file = NULL;
142 *line = 0;
143 #endif
144 }
145
146 struct bug_entry *find_bug(unsigned long bugaddr)
147 {
148 struct bug_entry *bug;
149
150 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
151 if (bugaddr == bug_addr(bug))
152 return bug;
153
154 return module_find_bug(bugaddr);
155 }
156
157 static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
158 {
159 struct bug_entry *bug;
160 const char *file;
161 unsigned line, warning, once, done;
162
163 if (!is_valid_bugaddr(bugaddr))
164 return BUG_TRAP_TYPE_NONE;
165
166 bug = find_bug(bugaddr);
167 if (!bug)
168 return BUG_TRAP_TYPE_NONE;
169
170 disable_trace_on_warning();
171
172 bug_get_file_line(bug, &file, &line);
173
174 warning = (bug->flags & BUGFLAG_WARNING) != 0;
175 once = (bug->flags & BUGFLAG_ONCE) != 0;
176 done = (bug->flags & BUGFLAG_DONE) != 0;
177
178 if (warning && once) {
179 if (done)
180 return BUG_TRAP_TYPE_WARN;
181
182 /*
183 * Since this is the only store, concurrency is not an issue.
184 */
185 bug->flags |= BUGFLAG_DONE;
186 }
187
188 /*
189 * BUG() and WARN_ON() families don't print a custom debug message
190 * before triggering the exception handler, so we must add the
191 * "cut here" line now. WARN() issues its own "cut here" before the
192 * extra debugging message it writes before triggering the handler.
193 */
194 if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
195 printk(KERN_DEFAULT CUT_HERE);
196
197 if (warning) {
198 /* this is a WARN_ON rather than BUG/BUG_ON */
199 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
200 NULL);
201 return BUG_TRAP_TYPE_WARN;
202 }
203
204 if (file)
205 pr_crit("kernel BUG at %s:%u!\n", file, line);
206 else
207 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
208 (void *)bugaddr);
209
210 return BUG_TRAP_TYPE_BUG;
211 }
212
213 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
214 {
215 enum bug_trap_type ret;
216 bool rcu = false;
217
218 rcu = warn_rcu_enter();
219 ret = __report_bug(bugaddr, regs);
220 warn_rcu_exit(rcu);
221
222 return ret;
223 }
224
225 static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
226 {
227 struct bug_entry *bug;
228
229 for (bug = start; bug < end; bug++)
230 bug->flags &= ~BUGFLAG_DONE;
231 }
232
233 void generic_bug_clear_once(void)
234 {
235 #ifdef CONFIG_MODULES
236 struct module *mod;
237
238 rcu_read_lock_sched();
239 list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
240 clear_once_table(mod->bug_table,
241 mod->bug_table + mod->num_bugs);
242 rcu_read_unlock_sched();
243 #endif
244
245 clear_once_table(__start___bug_table, __stop___bug_table);
246 }
247
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