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v6.2
  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
 51extern struct bug_entry __start___bug_table[], __stop___bug_table[];
 52
 53static 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 */
 64static LIST_HEAD(module_bug_list);
 65
 66static 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;
 81out:
 82	rcu_read_unlock_sched();
 83
 84	return bug;
 85}
 86
 87void 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
116void module_bug_cleanup(struct module *mod)
117{
118	list_del_rcu(&mod->bug_list);
119}
120
121#else
122
123static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
124{
125	return NULL;
126}
127#endif
128
129void 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
145struct 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
156enum 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
212static 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
220void 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}
v6.8
  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}