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
52extern struct bug_entry __start___bug_table[], __stop___bug_table[];
53
54static 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 */
65static LIST_HEAD(module_bug_list);
66
67static 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;
82out:
83	rcu_read_unlock_sched();
84
85	return bug;
86}
87
88void 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
117void module_bug_cleanup(struct module *mod)
118{
119	list_del_rcu(&mod->bug_list);
120}
121
122#else
123
124static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
125{
126	return NULL;
127}
128#endif
129
130void 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
146struct 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
157static 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
213enum 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
225static 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
233void 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