lib/bug.c

   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 }