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 52 extern struct bug_entry __start___bug_table[], __stop___bug_table[]; 53 54 static 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 */ 65 static LIST_HEAD(module_bug_list); 66 67 static 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 84 void 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 } 112 113 void module_bug_cleanup(struct module *mod) 114 { 115 list_del_rcu(&mod->bug_list); 116 } 117 118 #else 119 120 static inline struct bug_entry *module_find_bug(unsigned long bugaddr) 121 { 122 return NULL; 123 } 124 #endif 125 126 void 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 } 141 142 static 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 } 164 165 struct 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 } 175 176 static void __warn_printf(const char *fmt, struct pt_regs *regs) 177 { 178 if (!fmt) 179 return; 180 181 #ifdef HAVE_ARCH_BUG_FORMAT_ARGS 182 if (regs) { 183 struct arch_va_list _args; 184 va_list *args = __warn_args(&_args, regs); 185 186 if (args) { 187 vprintk(fmt, *args); 188 return; 189 } 190 } 191 #endif 192 193 printk("%s", fmt); 194 } 195 196 static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long bugaddr, struct pt_regs *regs) 197 { 198 bool warning, once, done, no_cut, has_args; 199 const char *file, *fmt; 200 unsigned line; 201 202 if (!bug) { 203 if (!is_valid_bugaddr(bugaddr)) 204 return BUG_TRAP_TYPE_NONE; 205 206 bug = find_bug(bugaddr); 207 if (!bug) 208 return BUG_TRAP_TYPE_NONE; 209 } 210 211 disable_trace_on_warning(); 212 213 bug_get_file_line(bug, &file, &line); 214 fmt = bug_get_format(bug); 215 216 warning = bug->flags & BUGFLAG_WARNING; 217 once = bug->flags & BUGFLAG_ONCE; 218 done = bug->flags & BUGFLAG_DONE; 219 no_cut = bug->flags & BUGFLAG_NO_CUT_HERE; 220 has_args = bug->flags & BUGFLAG_ARGS; 221 222 if (warning && once) { 223 if (done) 224 return BUG_TRAP_TYPE_WARN; 225 226 /* 227 * Since this is the only store, concurrency is not an issue. 228 */ 229 bug->flags |= BUGFLAG_DONE; 230 } 231 232 /* 233 * BUG() and WARN_ON() families don't print a custom debug message 234 * before triggering the exception handler, so we must add the 235 * "cut here" line now. WARN() issues its own "cut here" before the 236 * extra debugging message it writes before triggering the handler. 237 */ 238 if (!no_cut) { 239 printk(KERN_DEFAULT CUT_HERE); 240 __warn_printf(fmt, has_args ? regs : NULL); 241 } 242 243 if (warning) { 244 /* this is a WARN_ON rather than BUG/BUG_ON */ 245 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs, 246 NULL); 247 return BUG_TRAP_TYPE_WARN; 248 } 249 250 if (file) 251 pr_crit("kernel BUG at %s:%u!\n", file, line); 252 else 253 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n", 254 (void *)bugaddr); 255 256 return BUG_TRAP_TYPE_BUG; 257 } 258 259 enum bug_trap_type report_bug_entry(struct bug_entry *bug, struct pt_regs *regs) 260 { 261 enum bug_trap_type ret; 262 bool rcu = false; 263 264 rcu = warn_rcu_enter(); 265 ret = __report_bug(bug, 0, regs); 266 warn_rcu_exit(rcu); 267 268 return ret; 269 } 270 271 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs) 272 { 273 enum bug_trap_type ret; 274 bool rcu = false; 275 276 rcu = warn_rcu_enter(); 277 ret = __report_bug(NULL, bugaddr, regs); 278 warn_rcu_exit(rcu); 279 280 return ret; 281 } 282 283 static void clear_once_table(struct bug_entry *start, struct bug_entry *end) 284 { 285 struct bug_entry *bug; 286 287 for (bug = start; bug < end; bug++) 288 bug->flags &= ~BUGFLAG_DONE; 289 } 290 291 void generic_bug_clear_once(void) 292 { 293 #ifdef CONFIG_MODULES 294 struct module *mod; 295 296 scoped_guard(rcu) { 297 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) 298 clear_once_table(mod->bug_table, 299 mod->bug_table + mod->num_bugs); 300 } 301 #endif 302 303 clear_once_table(__start___bug_table, __stop___bug_table); 304 } 305