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 pointers relative to
10 the containing struct bug_entry for bug_addr and file.
11 CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG
12
13 CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
14 (though they're generally always on).
15
16 CONFIG_GENERIC_BUG is set by each architecture using this code.
17
18 To use this, your architecture must:
19
20 1. Set up the config options:
21 - Enable CONFIG_GENERIC_BUG if CONFIG_BUG
22
23 2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)
24 - Define HAVE_ARCH_BUG
25 - Implement BUG() to generate a faulting instruction
26 - NOTE: struct bug_entry does not have "file" or "line" entries
27 when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
28 the values accordingly.
29
30 3. Implement the trap
31 - In the illegal instruction trap handler (typically), verify
32 that the fault was in kernel mode, and call report_bug()
33 - report_bug() will return whether it was a false alarm, a warning,
34 or an actual bug.
35 - You must implement the is_valid_bugaddr(bugaddr) callback which
36 returns true if the eip is a real kernel address, and it points
37 to the expected BUG trap instruction.
38
39 Jeremy Fitzhardinge <jeremy@goop.org> 2006
40 */
41
42 #define pr_fmt(fmt) fmt
43
44 #include <linux/list.h>
45 #include <linux/module.h>
46 #include <linux/kernel.h>
47 #include <linux/bug.h>
48 #include <linux/sched.h>
49 #include <linux/rculist.h>
50 #include <linux/ftrace.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 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
57 return bug->bug_addr;
58 #else
59 return (unsigned long)bug + bug->bug_addr_disp;
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 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
module_bug_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)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 lockdep_assert_held(&module_mutex);
95
96 mod->bug_table = NULL;
97 mod->num_bugs = 0;
98
99 /* Find the __bug_table section, if present */
100 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
101 for (i = 1; i < hdr->e_shnum; i++) {
102 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
103 continue;
104 mod->bug_table = (void *) sechdrs[i].sh_addr;
105 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
106 break;
107 }
108
109 /*
110 * Strictly speaking this should have a spinlock to protect against
111 * traversals, but since we only traverse on BUG()s, a spinlock
112 * could potentially lead to deadlock and thus be counter-productive.
113 * Thus, this uses RCU to safely manipulate the bug list, since BUG
114 * must run in non-interruptive state.
115 */
116 list_add_rcu(&mod->bug_list, &module_bug_list);
117 }
118
module_bug_cleanup(struct module * mod)119 void module_bug_cleanup(struct module *mod)
120 {
121 lockdep_assert_held(&module_mutex);
122 list_del_rcu(&mod->bug_list);
123 }
124
125 #else
126
module_find_bug(unsigned long bugaddr)127 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
128 {
129 return NULL;
130 }
131 #endif
132
find_bug(unsigned long bugaddr)133 struct bug_entry *find_bug(unsigned long bugaddr)
134 {
135 struct bug_entry *bug;
136
137 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
138 if (bugaddr == bug_addr(bug))
139 return bug;
140
141 return module_find_bug(bugaddr);
142 }
143
report_bug(unsigned long bugaddr,struct pt_regs * regs)144 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
145 {
146 struct bug_entry *bug;
147 const char *file;
148 unsigned line, warning, once, done;
149
150 if (!is_valid_bugaddr(bugaddr))
151 return BUG_TRAP_TYPE_NONE;
152
153 bug = find_bug(bugaddr);
154 if (!bug)
155 return BUG_TRAP_TYPE_NONE;
156
157 disable_trace_on_warning();
158
159 file = NULL;
160 line = 0;
161 warning = 0;
162
163 if (bug) {
164 #ifdef CONFIG_DEBUG_BUGVERBOSE
165 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
166 file = bug->file;
167 #else
168 file = (const char *)bug + bug->file_disp;
169 #endif
170 line = bug->line;
171 #endif
172 warning = (bug->flags & BUGFLAG_WARNING) != 0;
173 once = (bug->flags & BUGFLAG_ONCE) != 0;
174 done = (bug->flags & BUGFLAG_DONE) != 0;
175
176 if (warning && once) {
177 if (done)
178 return BUG_TRAP_TYPE_WARN;
179
180 /*
181 * Since this is the only store, concurrency is not an issue.
182 */
183 bug->flags |= BUGFLAG_DONE;
184 }
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
