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(new: &mod->bug_list, head: &module_bug_list); |
115 | } |
116 | |
117 | void module_bug_cleanup(struct module *mod) |
118 | { |
119 | list_del_rcu(entry: &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(addr: 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: &file, line: &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, caller: (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(start: mod->bug_table, |
241 | end: mod->bug_table + mod->num_bugs); |
242 | rcu_read_unlock_sched(); |
243 | #endif |
244 | |
245 | clear_once_table(start: __start___bug_table, end: __stop___bug_table); |
246 | } |
247 | |