247 lines · c
1// SPDX-License-Identifier: GPL-2.02/*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 file10 CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG11 12 CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable13 (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_BUG21 22 2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)23 - Define HAVE_ARCH_BUG24 - Implement BUG() to generate a faulting instruction25 - NOTE: struct bug_entry does not have "file" or "line" entries26 when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate27 the values accordingly.28 29 3. Implement the trap30 - In the illegal instruction trap handler (typically), verify31 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 which35 returns true if the eip is a real kernel address, and it points36 to the expected BUG trap instruction.37 38 Jeremy Fitzhardinge <jeremy@goop.org> 200639 */40 41#define pr_fmt(fmt) fmt42 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_POINTERS57 return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;58#else59 return bug->bug_addr;60#endif61}62 63#ifdef CONFIG_MODULES64/* 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 against109 * traversals, but since we only traverse on BUG()s, a spinlock110 * could potentially lead to deadlock and thus be counter-productive.111 * Thus, this uses RCU to safely manipulate the bug list, since BUG112 * 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#else123 124static inline struct bug_entry *module_find_bug(unsigned long bugaddr)125{126 return NULL;127}128#endif129 130void bug_get_file_line(struct bug_entry *bug, const char **file,131 unsigned int *line)132{133#ifdef CONFIG_DEBUG_BUGVERBOSE134#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS135 *file = (const char *)&bug->file_disp + bug->file_disp;136#else137 *file = bug->file;138#endif139 *line = bug->line;140#else141 *file = NULL;142 *line = 0;143#endif144}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 message190 * before triggering the exception handler, so we must add the191 * "cut here" line now. WARN() issues its own "cut here" before the192 * 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 else207 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_MODULES236 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#endif244 245 clear_once_table(__start___bug_table, __stop___bug_table);246}247