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
142struct bug_entry *find_bug(unsigned long bugaddr)
143{
144 struct bug_entry *bug;
145
146 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
147 if (bugaddr == bug_addr(bug))
148 return bug;
149
150 return module_find_bug(bugaddr);
151}
152
153static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
154{
155 struct bug_entry *bug;
156 const char *file;
157 unsigned line, warning, once, done;
158
159 if (!is_valid_bugaddr(addr: bugaddr))
160 return BUG_TRAP_TYPE_NONE;
161
162 bug = find_bug(bugaddr);
163 if (!bug)
164 return BUG_TRAP_TYPE_NONE;
165
166 disable_trace_on_warning();
167
168 bug_get_file_line(bug, file: &file, line: &line);
169
170 warning = (bug->flags & BUGFLAG_WARNING) != 0;
171 once = (bug->flags & BUGFLAG_ONCE) != 0;
172 done = (bug->flags & BUGFLAG_DONE) != 0;
173
174 if (warning && once) {
175 if (done)
176 return BUG_TRAP_TYPE_WARN;
177
178 /*
179 * Since this is the only store, concurrency is not an issue.
180 */
181 bug->flags |= BUGFLAG_DONE;
182 }
183
184 /*
185 * BUG() and WARN_ON() families don't print a custom debug message
186 * before triggering the exception handler, so we must add the
187 * "cut here" line now. WARN() issues its own "cut here" before the
188 * extra debugging message it writes before triggering the handler.
189 */
190 if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
191 printk(KERN_DEFAULT CUT_HERE);
192
193 if (warning) {
194 /* this is a WARN_ON rather than BUG/BUG_ON */
195 __warn(file, line, caller: (void *)bugaddr, BUG_GET_TAINT(bug), regs,
196 NULL);
197 return BUG_TRAP_TYPE_WARN;
198 }
199
200 if (file)
201 pr_crit("kernel BUG at %s:%u!\n", file, line);
202 else
203 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
204 (void *)bugaddr);
205
206 return BUG_TRAP_TYPE_BUG;
207}
208
209enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
210{
211 enum bug_trap_type ret;
212 bool rcu = false;
213
214 rcu = warn_rcu_enter();
215 ret = __report_bug(bugaddr, regs);
216 warn_rcu_exit(rcu);
217
218 return ret;
219}
220
221static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
222{
223 struct bug_entry *bug;
224
225 for (bug = start; bug < end; bug++)
226 bug->flags &= ~BUGFLAG_DONE;
227}
228
229void generic_bug_clear_once(void)
230{
231#ifdef CONFIG_MODULES
232 struct module *mod;
233
234 scoped_guard(rcu) {
235 list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
236 clear_once_table(start: mod->bug_table,
237 end: mod->bug_table + mod->num_bugs);
238 }
239#endif
240
241 clear_once_table(start: __start___bug_table, end: __stop___bug_table);
242}
243