| 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 | if (!bug) |
| 154 | return BUG_TRAP_TYPE_NONE; |
| 155 | |
| 156 | file = NULL; |
| 157 | line = 0; |
| 158 | warning = 0; |
| 159 | |
| 160 | if (bug) { |
| 161 | #ifdef CONFIG_DEBUG_BUGVERBOSE |
| 162 | #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS |
| 163 | file = bug->file; |
| 164 | #else |
| 165 | file = (const char *)bug + bug->file_disp; |
| 166 | #endif |
| 167 | line = bug->line; |
| 168 | #endif |
| 169 | warning = (bug->flags & BUGFLAG_WARNING) != 0; |
| 170 | once = (bug->flags & BUGFLAG_ONCE) != 0; |
| 171 | done = (bug->flags & BUGFLAG_DONE) != 0; |
| 172 | |
| 173 | if (warning && once) { |
| 174 | if (done) |
| 175 | return BUG_TRAP_TYPE_WARN; |
| 176 | |
| 177 | /* |
| 178 | * Since this is the only store, concurrency is not an issue. |
| 179 | */ |
| 180 | bug->flags |= BUGFLAG_DONE; |
| 181 | } |
| 182 | } |
| 183 | |
| 184 | /* |
| 185 | * BUG() and WARN_ON() families don't print a custom debug message |
| 186 | * before triggering the exception handler, so we must add the |
| 187 | * "cut here" line now. WARN() issues its own "cut here" before the |
| 188 | * extra debugging message it writes before triggering the handler. |
| 189 | */ |
| 190 | if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0) |
| 191 | printk(KERN_DEFAULT CUT_HERE); |
| 192 | |
| 193 | if (warning) { |
| 194 | /* this is a WARN_ON rather than BUG/BUG_ON */ |
| 195 | __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs, |
| 196 | NULL); |
| 197 | return BUG_TRAP_TYPE_WARN; |
| 198 | } |
| 199 | |
| 200 | if (file) |
| 201 | pr_crit("kernel BUG at %s:%u!\n", file, line); |
| 202 | else |
| 203 | pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n", |
| 204 | (void *)bugaddr); |
| 205 | |
| 206 | return BUG_TRAP_TYPE_BUG; |
| 207 | } |
| 208 | |
| 209 | static void clear_once_table(struct bug_entry *start, struct bug_entry *end) |
| 210 | { |
| 211 | struct bug_entry *bug; |
| 212 | |
| 213 | for (bug = start; bug < end; bug++) |
| 214 | bug->flags &= ~BUGFLAG_DONE; |
| 215 | } |
| 216 | |
| 217 | void generic_bug_clear_once(void) |
| 218 | { |
| 219 | #ifdef CONFIG_MODULES |
| 220 | struct module *mod; |
| 221 | |
| 222 | rcu_read_lock_sched(); |
| 223 | list_for_each_entry_rcu(mod, &module_bug_list, bug_list) |
| 224 | clear_once_table(mod->bug_table, |
| 225 | mod->bug_table + mod->num_bugs); |
| 226 | rcu_read_unlock_sched(); |
| 227 | #endif |
| 228 | |
| 229 | clear_once_table(__start___bug_table, __stop___bug_table); |
| 230 | } |