summaryrefslogtreecommitdiffstats
path: root/lib/bug.c
blob: bc3656e944d29bd431d1b0fb8629f0ff090c676d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
/*
  Generic support for BUG()

  This respects the following config options:

  CONFIG_BUG - emit BUG traps.  Nothing happens without this.
  CONFIG_GENERIC_BUG - enable this code.
  CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit pointers relative to
	the containing struct bug_entry for bug_addr and file.
  CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG

  CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
  (though they're generally always on).

  CONFIG_GENERIC_BUG is set by each architecture using this code.

  To use this, your architecture must:

  1. Set up the config options:
     - Enable CONFIG_GENERIC_BUG if CONFIG_BUG

  2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)
     - Define HAVE_ARCH_BUG
     - Implement BUG() to generate a faulting instruction
     - NOTE: struct bug_entry does not have "file" or "line" entries
       when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
       the values accordingly.

  3. Implement the trap
     - In the illegal instruction trap handler (typically), verify
       that the fault was in kernel mode, and call report_bug()
     - report_bug() will return whether it was a false alarm, a warning,
       or an actual bug.
     - You must implement the is_valid_bugaddr(bugaddr) callback which
       returns true if the eip is a real kernel address, and it points
       to the expected BUG trap instruction.

    Jeremy Fitzhardinge <jeremy@goop.org> 2006
 */

#define pr_fmt(fmt) fmt

#include <linux/list.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bug.h>
#include <linux/sched.h>

extern const struct bug_entry __start___bug_table[], __stop___bug_table[];

static inline unsigned long bug_addr(const struct bug_entry *bug)
{
#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
	return bug->bug_addr;
#else
	return (unsigned long)bug + bug->bug_addr_disp;
#endif
}

#ifdef CONFIG_MODULES
/* Updates are protected by module mutex */
static LIST_HEAD(module_bug_list);

static const struct bug_entry *module_find_bug(unsigned long bugaddr)
{
	struct module *mod;
	const struct bug_entry *bug = NULL;

	rcu_read_lock_sched();
	list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
		unsigned i;

		bug = mod->bug_table;
		for (i = 0; i < mod->num_bugs; ++i, ++bug)
			if (bugaddr == bug_addr(bug))
				goto out;
	}
	bug = NULL;
out:
	rcu_read_unlock_sched();

	return bug;
}

void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
			 struct module *mod)
{
	char *secstrings;
	unsigned int i;

	lockdep_assert_held(&module_mutex);

	mod->bug_table = NULL;
	mod->num_bugs = 0;

	/* Find the __bug_table section, if present */
	secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
	for (i = 1; i < hdr->e_shnum; i++) {
		if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
			continue;
		mod->bug_table = (void *) sechdrs[i].sh_addr;
		mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
		break;
	}

	/*
	 * Strictly speaking this should have a spinlock to protect against
	 * traversals, but since we only traverse on BUG()s, a spinlock
	 * could potentially lead to deadlock and thus be counter-productive.
	 * Thus, this uses RCU to safely manipulate the bug list, since BUG
	 * must run in non-interruptive state.
	 */
	list_add_rcu(&mod->bug_list, &module_bug_list);
}

void module_bug_cleanup(struct module *mod)
{
	lockdep_assert_held(&module_mutex);
	list_del_rcu(&mod->bug_list);
}

#else

static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
{
	return NULL;
}
#endif

const struct bug_entry *find_bug(unsigned long bugaddr)
{
	const struct bug_entry *bug;

	for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
		if (bugaddr == bug_addr(bug))
			return bug;

	return module_find_bug(bugaddr);
}

enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
{
	const struct bug_entry *bug;
	const char *file;
	unsigned line, warning;

	if (!is_valid_bugaddr(bugaddr))
		return BUG_TRAP_TYPE_NONE;

	bug = find_bug(bugaddr);

	file = NULL;
	line = 0;
	warning = 0;

	if (bug) {
#ifdef CONFIG_DEBUG_BUGVERBOSE
#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
		file = bug->file;
#else
		file = (const char *)bug + bug->file_disp;
#endif
		line = bug->line;
#endif
		warning = (bug->flags & BUGFLAG_WARNING) != 0;
	}

	if (warning) {
		/* this is a WARN_ON rather than BUG/BUG_ON */
		__warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
		       NULL);
		return BUG_TRAP_TYPE_WARN;
	}

	printk(KERN_DEFAULT "------------[ cut here ]------------\n");

	if (file)
		pr_crit("kernel BUG at %s:%u!\n", file, line);
	else
		pr_crit("Kernel BUG at %p [verbose debug info unavailable]\n",
			(void *)bugaddr);

	return BUG_TRAP_TYPE_BUG;
}