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 pointers relative to 10 the containing struct bug_entry for bug_addr and file. 11 CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG 12 13 CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable 14 (though they're generally always on). 15 16 CONFIG_GENERIC_BUG is set by each architecture using this code. 17 18 To use this, your architecture must: 19 20 1. Set up the config options: 21 - Enable CONFIG_GENERIC_BUG if CONFIG_BUG 22 23 2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON) 24 - Define HAVE_ARCH_BUG 25 - Implement BUG() to generate a faulting instruction 26 - NOTE: struct bug_entry does not have "file" or "line" entries 27 when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate 28 the values accordingly. 29 30 3. Implement the trap 31 - In the illegal instruction trap handler (typically), verify 32 that the fault was in kernel mode, and call report_bug() 33 - report_bug() will return whether it was a false alarm, a warning, 34 or an actual bug. 35 - You must implement the is_valid_bugaddr(bugaddr) callback which 36 returns true if the eip is a real kernel address, and it points 37 to the expected BUG trap instruction. 38 39 Jeremy Fitzhardinge <jeremy@goop.org> 2006 40 */ 41 42 #define pr_fmt(fmt) fmt 43 44 #include <linux/list.h> 45 #include <linux/module.h> 46 #include <linux/kernel.h> 47 #include <linux/bug.h> 48 #include <linux/sched.h> 49 #include <linux/rculist.h> 50 51 extern struct bug_entry __start___bug_table[], __stop___bug_table[]; 52 53 static inline unsigned long bug_addr(const struct bug_entry *bug) 54 { 55 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS 56 return bug->bug_addr; 57 #else 58 return (unsigned long)bug + bug->bug_addr_disp; 59 #endif 60 } 61 62 #ifdef CONFIG_MODULES 63 /* Updates are protected by module mutex */ 64 static LIST_HEAD(module_bug_list); 65 66 static struct bug_entry *module_find_bug(unsigned long bugaddr) 67 { 68 struct module *mod; 69 struct bug_entry *bug = NULL; 70 71 rcu_read_lock_sched(); 72 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) { 73 unsigned i; 74 75 bug = mod->bug_table; 76 for (i = 0; i < mod->num_bugs; ++i, ++bug) 77 if (bugaddr == bug_addr(bug)) 78 goto out; 79 } 80 bug = NULL; 81 out: 82 rcu_read_unlock_sched(); 83 84 return bug; 85 } 86 87 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, 88 struct module *mod) 89 { 90 char *secstrings; 91 unsigned int i; 92 93 lockdep_assert_held(&module_mutex); 94 95 mod->bug_table = NULL; 96 mod->num_bugs = 0; 97 98 /* Find the __bug_table section, if present */ 99 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset; 100 for (i = 1; i < hdr->e_shnum; i++) { 101 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table")) 102 continue; 103 mod->bug_table = (void *) sechdrs[i].sh_addr; 104 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry); 105 break; 106 } 107 108 /* 109 * Strictly speaking this should have a spinlock to protect against 110 * traversals, but since we only traverse on BUG()s, a spinlock 111 * could potentially lead to deadlock and thus be counter-productive. 112 * Thus, this uses RCU to safely manipulate the bug list, since BUG 113 * must run in non-interruptive state. 114 */ 115 list_add_rcu(&mod->bug_list, &module_bug_list); 116 } 117 118 void module_bug_cleanup(struct module *mod) 119 { 120 lockdep_assert_held(&module_mutex); 121 list_del_rcu(&mod->bug_list); 122 } 123 124 #else 125 126 static inline struct bug_entry *module_find_bug(unsigned long bugaddr) 127 { 128 return NULL; 129 } 130 #endif 131 132 struct bug_entry *find_bug(unsigned long bugaddr) 133 { 134 struct bug_entry *bug; 135 136 for (bug = __start___bug_table; bug < __stop___bug_table; ++bug) 137 if (bugaddr == bug_addr(bug)) 138 return bug; 139 140 return module_find_bug(bugaddr); 141 } 142 143 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs) 144 { 145 struct bug_entry *bug; 146 const char *file; 147 unsigned line, warning, once, done; 148 149 if (!is_valid_bugaddr(bugaddr)) 150 return BUG_TRAP_TYPE_NONE; 151 152 bug = find_bug(bugaddr); 153 154 file = NULL; 155 line = 0; 156 warning = 0; 157 158 if (bug) { 159 #ifdef CONFIG_DEBUG_BUGVERBOSE 160 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS 161 file = bug->file; 162 #else 163 file = (const char *)bug + bug->file_disp; 164 #endif 165 line = bug->line; 166 #endif 167 warning = (bug->flags & BUGFLAG_WARNING) != 0; 168 once = (bug->flags & BUGFLAG_ONCE) != 0; 169 done = (bug->flags & BUGFLAG_DONE) != 0; 170 171 if (warning && once) { 172 if (done) 173 return BUG_TRAP_TYPE_WARN; 174 175 /* 176 * Since this is the only store, concurrency is not an issue. 177 */ 178 bug->flags |= BUGFLAG_DONE; 179 } 180 } 181 182 if (warning) { 183 /* this is a WARN_ON rather than BUG/BUG_ON */ 184 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs, 185 NULL); 186 return BUG_TRAP_TYPE_WARN; 187 } 188 189 printk(KERN_DEFAULT CUT_HERE); 190 191 if (file) 192 pr_crit("kernel BUG at %s:%u!\n", file, line); 193 else 194 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n", 195 (void *)bugaddr); 196 197 return BUG_TRAP_TYPE_BUG; 198 } 199 200 static void clear_once_table(struct bug_entry *start, struct bug_entry *end) 201 { 202 struct bug_entry *bug; 203 204 for (bug = start; bug < end; bug++) 205 bug->flags &= ~BUGFLAG_DONE; 206 } 207 208 void generic_bug_clear_once(void) 209 { 210 #ifdef CONFIG_MODULES 211 struct module *mod; 212 213 rcu_read_lock_sched(); 214 list_for_each_entry_rcu(mod, &module_bug_list, bug_list) 215 clear_once_table(mod->bug_table, 216 mod->bug_table + mod->num_bugs); 217 rcu_read_unlock_sched(); 218 #endif 219 220 clear_once_table(__start___bug_table, __stop___bug_table); 221 } 222