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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 :
54 974 : 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
59 974 : 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 :
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(&mod->bug_list, &module_bug_list);
115 : }
116 :
117 : void module_bug_cleanup(struct module *mod)
118 : {
119 : list_del_rcu(&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 0 : struct bug_entry *find_bug(unsigned long bugaddr)
131 : {
132 0 : struct bug_entry *bug;
133 :
134 973 : for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
135 974 : if (bugaddr == bug_addr(bug))
136 0 : return bug;
137 :
138 1 : return module_find_bug(bugaddr);
139 : }
140 :
141 1 : enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
142 : {
143 1 : struct bug_entry *bug;
144 1 : const char *file;
145 1 : unsigned line, warning, once, done;
146 :
147 1 : if (!is_valid_bugaddr(bugaddr))
148 : return BUG_TRAP_TYPE_NONE;
149 :
150 974 : bug = find_bug(bugaddr);
151 1 : if (!bug)
152 : return BUG_TRAP_TYPE_NONE;
153 :
154 1 : disable_trace_on_warning();
155 :
156 1 : file = NULL;
157 1 : line = 0;
158 1 : warning = 0;
159 :
160 1 : if (bug) {
161 : #ifdef CONFIG_DEBUG_BUGVERBOSE
162 : #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
163 : file = bug->file;
164 : #else
165 1 : file = (const char *)bug + bug->file_disp;
166 : #endif
167 1 : line = bug->line;
168 : #endif
169 1 : warning = (bug->flags & BUGFLAG_WARNING) != 0;
170 1 : once = (bug->flags & BUGFLAG_ONCE) != 0;
171 1 : done = (bug->flags & BUGFLAG_DONE) != 0;
172 :
173 1 : if (warning && once) {
174 0 : if (done)
175 : return BUG_TRAP_TYPE_WARN;
176 :
177 : /*
178 : * Since this is the only store, concurrency is not an issue.
179 : */
180 0 : bug->flags |= BUGFLAG_DONE;
181 : }
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 1 : if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
191 0 : printk(KERN_DEFAULT CUT_HERE);
192 :
193 1 : if (warning) {
194 : /* this is a WARN_ON rather than BUG/BUG_ON */
195 1 : __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
196 : NULL);
197 1 : return BUG_TRAP_TYPE_WARN;
198 : }
199 :
200 0 : if (file)
201 0 : pr_crit("kernel BUG at %s:%u!\n", file, line);
202 : else
203 0 : pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
204 : (void *)bugaddr);
205 :
206 : return BUG_TRAP_TYPE_BUG;
207 : }
208 :
209 0 : static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
210 : {
211 0 : struct bug_entry *bug;
212 :
213 0 : for (bug = start; bug < end; bug++)
214 0 : bug->flags &= ~BUGFLAG_DONE;
215 : }
216 :
217 0 : void generic_bug_clear_once(void)
218 : {
219 : #ifdef CONFIG_MODULES
220 : struct module *mod;
221 :
222 : rcu_read_lock_sched();
223 : list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
224 : clear_once_table(mod->bug_table,
225 : mod->bug_table + mod->num_bugs);
226 : rcu_read_unlock_sched();
227 : #endif
228 :
229 0 : clear_once_table(__start___bug_table, __stop___bug_table);
230 0 : }
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