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
51 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
52
bug_addr(const struct bug_entry * bug)53 static inline unsigned long bug_addr(const struct bug_entry *bug)
54 {
55 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
56 return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;
57 #else
58 return bug->bug_addr;
59 #endif
60 }
61
62 #ifdef CONFIG_MODULES
63 /* Updates are protected by module mutex */
64 static LIST_HEAD(module_bug_list);
65
module_find_bug(unsigned long bugaddr)66 static struct bug_entry *module_find_bug(unsigned long bugaddr)
67 {
68 struct module *mod;
69 struct bug_entry *bug = NULL;
70
71 rcu_read_lock_sched();
72 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
73 unsigned i;
74
75 bug = mod->bug_table;
76 for (i = 0; i < mod->num_bugs; ++i, ++bug)
77 if (bugaddr == bug_addr(bug))
78 goto out;
79 }
80 bug = NULL;
81 out:
82 rcu_read_unlock_sched();
83
84 return bug;
85 }
86
module_bug_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)87 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
88 struct module *mod)
89 {
90 char *secstrings;
91 unsigned int i;
92
93 mod->bug_table = NULL;
94 mod->num_bugs = 0;
95
96 /* Find the __bug_table section, if present */
97 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
98 for (i = 1; i < hdr->e_shnum; i++) {
99 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
100 continue;
101 mod->bug_table = (void *) sechdrs[i].sh_addr;
102 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
103 break;
104 }
105
106 /*
107 * Strictly speaking this should have a spinlock to protect against
108 * traversals, but since we only traverse on BUG()s, a spinlock
109 * could potentially lead to deadlock and thus be counter-productive.
110 * Thus, this uses RCU to safely manipulate the bug list, since BUG
111 * must run in non-interruptive state.
112 */
113 list_add_rcu(&mod->bug_list, &module_bug_list);
114 }
115
module_bug_cleanup(struct module * mod)116 void module_bug_cleanup(struct module *mod)
117 {
118 list_del_rcu(&mod->bug_list);
119 }
120
121 #else
122
module_find_bug(unsigned long bugaddr)123 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
124 {
125 return NULL;
126 }
127 #endif
128
bug_get_file_line(struct bug_entry * bug,const char ** file,unsigned int * line)129 void bug_get_file_line(struct bug_entry *bug, const char **file,
130 unsigned int *line)
131 {
132 #ifdef CONFIG_DEBUG_BUGVERBOSE
133 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
134 *file = (const char *)&bug->file_disp + bug->file_disp;
135 #else
136 *file = bug->file;
137 #endif
138 *line = bug->line;
139 #else
140 *file = NULL;
141 *line = 0;
142 #endif
143 }
144
find_bug(unsigned long bugaddr)145 struct bug_entry *find_bug(unsigned long bugaddr)
146 {
147 struct bug_entry *bug;
148
149 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
150 if (bugaddr == bug_addr(bug))
151 return bug;
152
153 return module_find_bug(bugaddr);
154 }
155
report_bug(unsigned long bugaddr,struct pt_regs * regs)156 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
157 {
158 struct bug_entry *bug;
159 const char *file;
160 unsigned line, warning, once, done;
161
162 if (!is_valid_bugaddr(bugaddr))
163 return BUG_TRAP_TYPE_NONE;
164
165 bug = find_bug(bugaddr);
166 if (!bug)
167 return BUG_TRAP_TYPE_NONE;
168
169 disable_trace_on_warning();
170
171 bug_get_file_line(bug, &file, &line);
172
173 warning = (bug->flags & BUGFLAG_WARNING) != 0;
174 once = (bug->flags & BUGFLAG_ONCE) != 0;
175 done = (bug->flags & BUGFLAG_DONE) != 0;
176
177 if (warning && once) {
178 if (done)
179 return BUG_TRAP_TYPE_WARN;
180
181 /*
182 * Since this is the only store, concurrency is not an issue.
183 */
184 bug->flags |= BUGFLAG_DONE;
185 }
186
187 /*
188 * BUG() and WARN_ON() families don't print a custom debug message
189 * before triggering the exception handler, so we must add the
190 * "cut here" line now. WARN() issues its own "cut here" before the
191 * extra debugging message it writes before triggering the handler.
192 */
193 if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
194 printk(KERN_DEFAULT CUT_HERE);
195
196 if (warning) {
197 /* this is a WARN_ON rather than BUG/BUG_ON */
198 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
199 NULL);
200 return BUG_TRAP_TYPE_WARN;
201 }
202
203 if (file)
204 pr_crit("kernel BUG at %s:%u!\n", file, line);
205 else
206 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
207 (void *)bugaddr);
208
209 return BUG_TRAP_TYPE_BUG;
210 }
211
clear_once_table(struct bug_entry * start,struct bug_entry * end)212 static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
213 {
214 struct bug_entry *bug;
215
216 for (bug = start; bug < end; bug++)
217 bug->flags &= ~BUGFLAG_DONE;
218 }
219
generic_bug_clear_once(void)220 void generic_bug_clear_once(void)
221 {
222 #ifdef CONFIG_MODULES
223 struct module *mod;
224
225 rcu_read_lock_sched();
226 list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
227 clear_once_table(mod->bug_table,
228 mod->bug_table + mod->num_bugs);
229 rcu_read_unlock_sched();
230 #endif
231
232 clear_once_table(__start___bug_table, __stop___bug_table);
233 }
234
