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 #include <trace/hooks/bug.h>
53
54 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
55
bug_addr(const struct bug_entry * bug)56 static inline unsigned long bug_addr(const struct bug_entry *bug)
57 {
58 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
59 return bug->bug_addr;
60 #else
61 return (unsigned long)bug + bug->bug_addr_disp;
62 #endif
63 }
64
65 #ifdef CONFIG_MODULES
66 /* Updates are protected by module mutex */
67 static LIST_HEAD(module_bug_list);
68
module_find_bug(unsigned long bugaddr)69 static struct bug_entry *module_find_bug(unsigned long bugaddr)
70 {
71 struct module *mod;
72 struct bug_entry *bug = NULL;
73
74 rcu_read_lock_sched();
75 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
76 unsigned i;
77
78 bug = mod->bug_table;
79 for (i = 0; i < mod->num_bugs; ++i, ++bug)
80 if (bugaddr == bug_addr(bug))
81 goto out;
82 }
83 bug = NULL;
84 out:
85 rcu_read_unlock_sched();
86
87 return bug;
88 }
89
module_bug_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)90 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
91 struct module *mod)
92 {
93 char *secstrings;
94 unsigned int i;
95
96 lockdep_assert_held(&module_mutex);
97
98 mod->bug_table = NULL;
99 mod->num_bugs = 0;
100
101 /* Find the __bug_table section, if present */
102 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
103 for (i = 1; i < hdr->e_shnum; i++) {
104 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
105 continue;
106 mod->bug_table = (void *) sechdrs[i].sh_addr;
107 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
108 break;
109 }
110
111 /*
112 * Strictly speaking this should have a spinlock to protect against
113 * traversals, but since we only traverse on BUG()s, a spinlock
114 * could potentially lead to deadlock and thus be counter-productive.
115 * Thus, this uses RCU to safely manipulate the bug list, since BUG
116 * must run in non-interruptive state.
117 */
118 list_add_rcu(&mod->bug_list, &module_bug_list);
119 }
120
module_bug_cleanup(struct module * mod)121 void module_bug_cleanup(struct module *mod)
122 {
123 lockdep_assert_held(&module_mutex);
124 list_del_rcu(&mod->bug_list);
125 }
126
127 #else
128
module_find_bug(unsigned long bugaddr)129 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
130 {
131 return NULL;
132 }
133 #endif
134
bug_get_file_line(struct bug_entry * bug,const char ** file,unsigned int * line)135 void bug_get_file_line(struct bug_entry *bug, const char **file,
136 unsigned int *line)
137 {
138 #ifdef CONFIG_DEBUG_BUGVERBOSE
139 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
140 *file = bug->file;
141 #else
142 *file = (const char *)bug + bug->file_disp;
143 #endif
144 *line = bug->line;
145 #else
146 *file = NULL;
147 *line = 0;
148 #endif
149 }
150
find_bug(unsigned long bugaddr)151 struct bug_entry *find_bug(unsigned long bugaddr)
152 {
153 struct bug_entry *bug;
154
155 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
156 if (bugaddr == bug_addr(bug))
157 return bug;
158
159 return module_find_bug(bugaddr);
160 }
161
report_bug(unsigned long bugaddr,struct pt_regs * regs)162 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
163 {
164 struct bug_entry *bug;
165 const char *file;
166 unsigned line, warning, once, done;
167
168 if (!is_valid_bugaddr(bugaddr))
169 return BUG_TRAP_TYPE_NONE;
170
171 bug = find_bug(bugaddr);
172 if (!bug)
173 return BUG_TRAP_TYPE_NONE;
174
175 disable_trace_on_warning();
176
177 bug_get_file_line(bug, &file, &line);
178
179 warning = (bug->flags & BUGFLAG_WARNING) != 0;
180 once = (bug->flags & BUGFLAG_ONCE) != 0;
181 done = (bug->flags & BUGFLAG_DONE) != 0;
182
183 if (warning && once) {
184 if (done)
185 return BUG_TRAP_TYPE_WARN;
186
187 /*
188 * Since this is the only store, concurrency is not an issue.
189 */
190 bug->flags |= BUGFLAG_DONE;
191 }
192
193 /*
194 * BUG() and WARN_ON() families don't print a custom debug message
195 * before triggering the exception handler, so we must add the
196 * "cut here" line now. WARN() issues its own "cut here" before the
197 * extra debugging message it writes before triggering the handler.
198 */
199 if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
200 printk(KERN_DEFAULT CUT_HERE);
201
202 if (warning) {
203 /* this is a WARN_ON rather than BUG/BUG_ON */
204 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
205 NULL);
206 return BUG_TRAP_TYPE_WARN;
207 }
208
209 if (file)
210 pr_crit("kernel BUG at %s:%u!\n", file, line);
211 else
212 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
213 (void *)bugaddr);
214
215 trace_android_rvh_report_bug(file, line, bugaddr);
216
217 return BUG_TRAP_TYPE_BUG;
218 }
219
clear_once_table(struct bug_entry * start,struct bug_entry * end)220 static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
221 {
222 struct bug_entry *bug;
223
224 for (bug = start; bug < end; bug++)
225 bug->flags &= ~BUGFLAG_DONE;
226 }
227
generic_bug_clear_once(void)228 void generic_bug_clear_once(void)
229 {
230 #ifdef CONFIG_MODULES
231 struct module *mod;
232
233 rcu_read_lock_sched();
234 list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
235 clear_once_table(mod->bug_table,
236 mod->bug_table + mod->num_bugs);
237 rcu_read_unlock_sched();
238 #endif
239
240 clear_once_table(__start___bug_table, __stop___bug_table);
241 }
242