xref: /openbmc/linux/lib/bug.c (revision 5a5d7e9b)
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 
bug_addr(const struct bug_entry * bug)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 
module_find_bug(unsigned long bugaddr)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 
module_bug_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)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 
module_bug_cleanup(struct module * mod)117 void module_bug_cleanup(struct module *mod)
118 {
119 	list_del_rcu(&mod->bug_list);
120 }
121 
122 #else
123 
module_find_bug(unsigned long bugaddr)124 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
125 {
126 	return NULL;
127 }
128 #endif
129 
bug_get_file_line(struct bug_entry * bug,const char ** file,unsigned int * line)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 
find_bug(unsigned long bugaddr)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 
__report_bug(unsigned long bugaddr,struct pt_regs * regs)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(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, &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, (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 
report_bug(unsigned long bugaddr,struct pt_regs * regs)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 
clear_once_table(struct bug_entry * start,struct bug_entry * end)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 
generic_bug_clear_once(void)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(mod->bug_table,
241 				 mod->bug_table + mod->num_bugs);
242 	rcu_read_unlock_sched();
243 #endif
244 
245 	clear_once_table(__start___bug_table, __stop___bug_table);
246 }
247