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 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 }