xref: /openbmc/linux/lib/bug.c (revision 82df5b73)
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 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 
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 	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 
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 
127 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
128 {
129 	return NULL;
130 }
131 #endif
132 
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 
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 
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 
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