bug.c

  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 bug_entry *bug;
 70	struct module *mod;
 71
 72	guard(rcu)();
 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				return bug;
 80	}
 81	return NULL;
 82}
 83
 84void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
 85			 struct module *mod)
 86{
 87	char *secstrings;
 88	unsigned int i;
 89
 90	mod->bug_table = NULL;
 91	mod->num_bugs = 0;
 92
 93	/* Find the __bug_table section, if present */
 94	secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
 95	for (i = 1; i < hdr->e_shnum; i++) {
 96		if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
 97			continue;
 98		mod->bug_table = (void *) sechdrs[i].sh_addr;
 99		mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
100		break;
101	}
102
103	/*
104	 * Strictly speaking this should have a spinlock to protect against
105	 * traversals, but since we only traverse on BUG()s, a spinlock
106	 * could potentially lead to deadlock and thus be counter-productive.
107	 * Thus, this uses RCU to safely manipulate the bug list, since BUG
108	 * must run in non-interruptive state.
109	 */
110	list_add_rcu(&mod->bug_list, &module_bug_list);
111}
112
113void module_bug_cleanup(struct module *mod)
114{
115	list_del_rcu(&mod->bug_list);
116}
117
118#else
119
120static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
121{
122	return NULL;
123}
124#endif
125
126void bug_get_file_line(struct bug_entry *bug, const char **file,
127		       unsigned int *line)
128{
129#ifdef CONFIG_DEBUG_BUGVERBOSE
130#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
131	*file = (const char *)&bug->file_disp + bug->file_disp;
132#else
133	*file = bug->file;
134#endif
135	*line = bug->line;
136#else
137	*file = NULL;
138	*line = 0;
139#endif
140}
141
142static const char *bug_get_format(struct bug_entry *bug)
143{
144	const char *format = NULL;
145#ifdef HAVE_ARCH_BUG_FORMAT
146#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
147	/*
148	 * Allow an architecture to:
149	 *  - relative encode NULL (difficult vs KASLR);
150	 *  - use a literal 0 (there are no valid objects inside
151	 *    the __bug_table itself to refer to after all);
152	 *  - use an empty string.
153	 */
154	if (bug->format_disp)
155		format = (const char *)&bug->format_disp + bug->format_disp;
156	if (format && format[0] == '\0')
157		format = NULL;
158#else
159	format = bug->format;
160#endif
161#endif
162	return format;
163}
164
165struct bug_entry *find_bug(unsigned long bugaddr)
166{
167	struct bug_entry *bug;
168
169	for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
170		if (bugaddr == bug_addr(bug))
171			return bug;
172
173	return module_find_bug(bugaddr);
174}
175
176static __printf(1, 0)
177void __warn_printf(const char *fmt, struct pt_regs *regs)
178{
179	if (!fmt)
180		return;
181
182#ifdef HAVE_ARCH_BUG_FORMAT_ARGS
183	if (regs) {
184		struct arch_va_list _args;
185		va_list *args = __warn_args(&_args, regs);
186
187		if (args) {
188			vprintk(fmt, *args);
189			return;
190		}
191	}
192#endif
193
194	printk("%s", fmt);
195}
196
197static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long bugaddr, struct pt_regs *regs)
198{
199	bool warning, once, done, no_cut, has_args;
200	const char *file, *fmt;
201	unsigned line;
202
203	if (!bug) {
204		if (!is_valid_bugaddr(bugaddr))
205			return BUG_TRAP_TYPE_NONE;
206
207		bug = find_bug(bugaddr);
208		if (!bug)
209			return BUG_TRAP_TYPE_NONE;
210	}
211
212	disable_trace_on_warning();
213
214	bug_get_file_line(bug, &file, &line);
215	fmt = bug_get_format(bug);
216
217	warning  = bug->flags & BUGFLAG_WARNING;
218	once     = bug->flags & BUGFLAG_ONCE;
219	done     = bug->flags & BUGFLAG_DONE;
220	no_cut   = bug->flags & BUGFLAG_NO_CUT_HERE;
221	has_args = bug->flags & BUGFLAG_ARGS;
222
223	if (warning && once) {
224		if (done)
225			return BUG_TRAP_TYPE_WARN;
226
227		/*
228		 * Since this is the only store, concurrency is not an issue.
229		 */
230		bug->flags |= BUGFLAG_DONE;
231	}
232
233	/*
234	 * BUG() and WARN_ON() families don't print a custom debug message
235	 * before triggering the exception handler, so we must add the
236	 * "cut here" line now. WARN() issues its own "cut here" before the
237	 * extra debugging message it writes before triggering the handler.
238	 */
239	if (!no_cut) {
240		printk(KERN_DEFAULT CUT_HERE);
241		__warn_printf(fmt, has_args ? regs : NULL);
242	}
243
244	if (warning) {
245		/* this is a WARN_ON rather than BUG/BUG_ON */
246		__warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
247		       NULL);
248		return BUG_TRAP_TYPE_WARN;
249	}
250
251	if (file)
252		pr_crit("kernel BUG at %s:%u!\n", file, line);
253	else
254		pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
255			(void *)bugaddr);
256
257	return BUG_TRAP_TYPE_BUG;
258}
259
260enum bug_trap_type report_bug_entry(struct bug_entry *bug, struct pt_regs *regs)
261{
262	enum bug_trap_type ret;
263	bool rcu = false;
264
265	rcu = warn_rcu_enter();
266	ret = __report_bug(bug, bug_addr(bug), regs);
267	warn_rcu_exit(rcu);
268
269	return ret;
270}
271
272enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
273{
274	enum bug_trap_type ret;
275	bool rcu = false;
276
277	rcu = warn_rcu_enter();
278	ret = __report_bug(NULL, bugaddr, regs);
279	warn_rcu_exit(rcu);
280
281	return ret;
282}
283
284static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
285{
286	struct bug_entry *bug;
287
288	for (bug = start; bug < end; bug++)
289		bug->flags &= ~BUGFLAG_DONE;
290}
291
292void generic_bug_clear_once(void)
293{
294#ifdef CONFIG_MODULES
295	struct module *mod;
296
297	scoped_guard(rcu) {
298		list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
299			clear_once_table(mod->bug_table,
300					 mod->bug_table + mod->num_bugs);
301	}
302#endif
303
304	clear_once_table(__start___bug_table, __stop___bug_table);
305}