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 
51 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
52 
bug_addr(const struct bug_entry * bug)53 static inline unsigned long bug_addr(const struct bug_entry *bug)
54 {
55 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
56 	return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;
57 #else
58 	return bug->bug_addr;
59 #endif
60 }
61 
62 #ifdef CONFIG_MODULES
63 /* Updates are protected by module mutex */
64 static LIST_HEAD(module_bug_list);
65 
module_find_bug(unsigned long bugaddr)66 static struct bug_entry *module_find_bug(unsigned long bugaddr)
67 {
68 	struct module *mod;
69 	struct bug_entry *bug = NULL;
70 
71 	rcu_read_lock_sched();
72 	list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
73 		unsigned i;
74 
75 		bug = mod->bug_table;
76 		for (i = 0; i < mod->num_bugs; ++i, ++bug)
77 			if (bugaddr == bug_addr(bug))
78 				goto out;
79 	}
80 	bug = NULL;
81 out:
82 	rcu_read_unlock_sched();
83 
84 	return bug;
85 }
86 
module_bug_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)87 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
88 			 struct module *mod)
89 {
90 	char *secstrings;
91 	unsigned int i;
92 
93 	mod->bug_table = NULL;
94 	mod->num_bugs = 0;
95 
96 	/* Find the __bug_table section, if present */
97 	secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
98 	for (i = 1; i < hdr->e_shnum; i++) {
99 		if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
100 			continue;
101 		mod->bug_table = (void *) sechdrs[i].sh_addr;
102 		mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
103 		break;
104 	}
105 
106 	/*
107 	 * Strictly speaking this should have a spinlock to protect against
108 	 * traversals, but since we only traverse on BUG()s, a spinlock
109 	 * could potentially lead to deadlock and thus be counter-productive.
110 	 * Thus, this uses RCU to safely manipulate the bug list, since BUG
111 	 * must run in non-interruptive state.
112 	 */
113 	list_add_rcu(&mod->bug_list, &module_bug_list);
114 }
115 
module_bug_cleanup(struct module * mod)116 void module_bug_cleanup(struct module *mod)
117 {
118 	list_del_rcu(&mod->bug_list);
119 }
120 
121 #else
122 
module_find_bug(unsigned long bugaddr)123 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
124 {
125 	return NULL;
126 }
127 #endif
128 
bug_get_file_line(struct bug_entry * bug,const char ** file,unsigned int * line)129 void bug_get_file_line(struct bug_entry *bug, const char **file,
130 		       unsigned int *line)
131 {
132 #ifdef CONFIG_DEBUG_BUGVERBOSE
133 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
134 	*file = (const char *)&bug->file_disp + bug->file_disp;
135 #else
136 	*file = bug->file;
137 #endif
138 	*line = bug->line;
139 #else
140 	*file = NULL;
141 	*line = 0;
142 #endif
143 }
144 
find_bug(unsigned long bugaddr)145 struct bug_entry *find_bug(unsigned long bugaddr)
146 {
147 	struct bug_entry *bug;
148 
149 	for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
150 		if (bugaddr == bug_addr(bug))
151 			return bug;
152 
153 	return module_find_bug(bugaddr);
154 }
155 
report_bug(unsigned long bugaddr,struct pt_regs * regs)156 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
157 {
158 	struct bug_entry *bug;
159 	const char *file;
160 	unsigned line, warning, once, done;
161 
162 	if (!is_valid_bugaddr(bugaddr))
163 		return BUG_TRAP_TYPE_NONE;
164 
165 	bug = find_bug(bugaddr);
166 	if (!bug)
167 		return BUG_TRAP_TYPE_NONE;
168 
169 	disable_trace_on_warning();
170 
171 	bug_get_file_line(bug, &file, &line);
172 
173 	warning = (bug->flags & BUGFLAG_WARNING) != 0;
174 	once = (bug->flags & BUGFLAG_ONCE) != 0;
175 	done = (bug->flags & BUGFLAG_DONE) != 0;
176 
177 	if (warning && once) {
178 		if (done)
179 			return BUG_TRAP_TYPE_WARN;
180 
181 		/*
182 		 * Since this is the only store, concurrency is not an issue.
183 		 */
184 		bug->flags |= BUGFLAG_DONE;
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 
clear_once_table(struct bug_entry * start,struct bug_entry * end)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 
generic_bug_clear_once(void)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