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 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; 82 out: 83 rcu_read_unlock_sched(); 84 85 return bug; 86 } 87 88 void 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 } 116 117 void module_bug_cleanup(struct module *mod) 118 { 119 list_del_rcu(&mod->bug_list); 120 } 121 122 #else 123 124 static inline struct bug_entry *module_find_bug(unsigned long bugaddr) 125 { 126 return NULL; 127 } 128 #endif 129 130 void 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 } 145 146 struct 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 } 156 157 static 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 } 212 213 enum 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 } 224 225 static 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 } 232 233 void 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 } 247