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 #include <kunit/test-bug.h> 52 53 extern struct bug_entry __start___bug_table[], __stop___bug_table[]; 54 55 static inline unsigned long bug_addr(const struct bug_entry *bug) 56 { 57 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS 58 return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp; 59 #else 60 return bug->bug_addr; 61 #endif 62 } 63 64 #ifdef CONFIG_MODULES 65 /* Updates are protected by module mutex */ 66 static LIST_HEAD(module_bug_list); 67 68 static struct bug_entry *module_find_bug(unsigned long bugaddr) 69 { 70 struct bug_entry *bug; 71 struct module *mod; 72 73 guard(rcu)(); 74 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) { 75 unsigned int i; 76 77 bug = mod->bug_table; 78 for (i = 0; i < mod->num_bugs; ++i, ++bug) 79 if (bugaddr == bug_addr(bug)) 80 return bug; 81 } 82 return NULL; 83 } 84 85 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, 86 struct module *mod) 87 { 88 char *secstrings; 89 unsigned int i; 90 91 mod->bug_table = NULL; 92 mod->num_bugs = 0; 93 94 /* Find the __bug_table section, if present */ 95 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset; 96 for (i = 1; i < hdr->e_shnum; i++) { 97 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table")) 98 continue; 99 mod->bug_table = (void *) sechdrs[i].sh_addr; 100 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry); 101 break; 102 } 103 104 /* 105 * Strictly speaking this should have a spinlock to protect against 106 * traversals, but since we only traverse on BUG()s, a spinlock 107 * could potentially lead to deadlock and thus be counter-productive. 108 * Thus, this uses RCU to safely manipulate the bug list, since BUG 109 * must run in non-interruptive state. 110 */ 111 list_add_rcu(&mod->bug_list, &module_bug_list); 112 } 113 114 void module_bug_cleanup(struct module *mod) 115 { 116 list_del_rcu(&mod->bug_list); 117 } 118 119 #else 120 121 static inline struct bug_entry *module_find_bug(unsigned long bugaddr) 122 { 123 return NULL; 124 } 125 #endif 126 127 void bug_get_file_line(struct bug_entry *bug, const char **file, 128 unsigned int *line) 129 { 130 #ifdef CONFIG_DEBUG_BUGVERBOSE 131 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS 132 *file = (const char *)&bug->file_disp + bug->file_disp; 133 #else 134 *file = bug->file; 135 #endif 136 *line = bug->line; 137 #else 138 *file = NULL; 139 *line = 0; 140 #endif 141 } 142 143 static const char *bug_get_format(struct bug_entry *bug) 144 { 145 const char *format = NULL; 146 #ifdef HAVE_ARCH_BUG_FORMAT 147 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS 148 /* 149 * Allow an architecture to: 150 * - relative encode NULL (difficult vs KASLR); 151 * - use a literal 0 (there are no valid objects inside 152 * the __bug_table itself to refer to after all); 153 * - use an empty string. 154 */ 155 if (bug->format_disp) 156 format = (const char *)&bug->format_disp + bug->format_disp; 157 if (format && format[0] == '\0') 158 format = NULL; 159 #else 160 format = bug->format; 161 #endif 162 #endif 163 return format; 164 } 165 166 struct bug_entry *find_bug(unsigned long bugaddr) 167 { 168 struct bug_entry *bug; 169 170 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug) 171 if (bugaddr == bug_addr(bug)) 172 return bug; 173 174 return module_find_bug(bugaddr); 175 } 176 177 static __printf(1, 0) 178 void __warn_printf(const char *fmt, struct pt_regs *regs) 179 { 180 if (!fmt) 181 return; 182 183 #ifdef HAVE_ARCH_BUG_FORMAT_ARGS 184 if (regs) { 185 struct arch_va_list _args; 186 va_list *args = __warn_args(&_args, regs); 187 188 if (args) { 189 vprintk(fmt, *args); 190 return; 191 } 192 } 193 #endif 194 195 pr_warn("%s", fmt); 196 } 197 198 static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long bugaddr, struct pt_regs *regs) 199 { 200 bool warning, once, done, no_cut, has_args; 201 const char *file, *fmt; 202 unsigned int line; 203 204 if (!bug) { 205 if (!is_valid_bugaddr(bugaddr)) 206 return BUG_TRAP_TYPE_NONE; 207 208 bug = find_bug(bugaddr); 209 if (!bug) 210 return BUG_TRAP_TYPE_NONE; 211 } 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 #ifdef CONFIG_KUNIT 223 /* 224 * Before the once logic so suppressed warnings do not consume 225 * the single-fire budget of WARN_ON_ONCE(). 226 */ 227 if (warning && kunit_is_suppressed_warning(true)) 228 return BUG_TRAP_TYPE_WARN; 229 #endif 230 231 disable_trace_on_warning(); 232 233 if (warning && once) { 234 if (done) 235 return BUG_TRAP_TYPE_WARN; 236 237 /* 238 * Since this is the only store, concurrency is not an issue. 239 */ 240 bug->flags |= BUGFLAG_DONE; 241 } 242 243 /* 244 * BUG() and WARN_ON() families don't print a custom debug message 245 * before triggering the exception handler, so we must add the 246 * "cut here" line now. WARN() issues its own "cut here" before the 247 * extra debugging message it writes before triggering the handler. 248 */ 249 if (!no_cut) { 250 pr_info(CUT_HERE); 251 __warn_printf(fmt, has_args ? regs : NULL); 252 } 253 254 if (warning) { 255 /* this is a WARN_ON rather than BUG/BUG_ON */ 256 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs, 257 NULL); 258 return BUG_TRAP_TYPE_WARN; 259 } 260 261 if (file) 262 pr_crit("kernel BUG at %s:%u!\n", file, line); 263 else 264 pr_crit("kernel BUG at %pB [verbose debug info unavailable]\n", 265 (void *)bugaddr); 266 267 return BUG_TRAP_TYPE_BUG; 268 } 269 270 enum bug_trap_type report_bug_entry(struct bug_entry *bug, struct pt_regs *regs) 271 { 272 enum bug_trap_type ret; 273 bool rcu; 274 275 rcu = warn_rcu_enter(); 276 ret = __report_bug(bug, bug_addr(bug), regs); 277 warn_rcu_exit(rcu); 278 279 return ret; 280 } 281 282 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs) 283 { 284 enum bug_trap_type ret; 285 bool rcu; 286 287 rcu = warn_rcu_enter(); 288 ret = __report_bug(NULL, bugaddr, regs); 289 warn_rcu_exit(rcu); 290 291 return ret; 292 } 293 294 static void clear_once_table(struct bug_entry *start, struct bug_entry *end) 295 { 296 struct bug_entry *bug; 297 298 for (bug = start; bug < end; bug++) 299 bug->flags &= ~BUGFLAG_DONE; 300 } 301 302 void generic_bug_clear_once(void) 303 { 304 #ifdef CONFIG_MODULES 305 struct module *mod; 306 307 scoped_guard(rcu) { 308 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) 309 clear_once_table(mod->bug_table, 310 mod->bug_table + mod->num_bugs); 311 } 312 #endif 313 314 clear_once_table(__start___bug_table, __stop___bug_table); 315 } 316