lib/bug.c

   1 /*
   2   Generic support for BUG()
   3
   4   This respects the following config options:
   5
   6   CONFIG_BUG - emit BUG traps.  Nothing happens without this.
   7   CONFIG_GENERIC_BUG - enable this code.
   8   CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit pointers relative to
   9         the containing struct bug_entry 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
  49 extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
  50
  51 static inline unsigned long bug_addr(const struct bug_entry *bug)
  52 {
  53 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
  54         return bug->bug_addr;
  55 #else
  56         return (unsigned long)bug + bug->bug_addr_disp;
  57 #endif
  58 }
  59
  60 #ifdef CONFIG_MODULES
  61 /* Updates are protected by module mutex */
  62 static LIST_HEAD(module_bug_list);
  63
  64 static const struct bug_entry *module_find_bug(unsigned long bugaddr)
  65 {
  66         struct module *mod;
  67         const struct bug_entry *bug = NULL;
  68
  69         rcu_read_lock_sched();
  70         list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
  71                 unsigned i;
  72
  73                 bug = mod->bug_table;
  74                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
  75                         if (bugaddr == bug_addr(bug))
  76                                 goto out;
  77         }
  78         bug = NULL;
  79 out:
  80         rcu_read_unlock_sched();
  81
  82         return bug;
  83 }
  84
  85 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  86                          struct module *mod)
  87 {
  88         char *secstrings;
  89         unsigned int i;
  90
  91         lockdep_assert_held(&module_mutex);
  92
  93         mod->bug_table = NULL;
  94         mod->num_bugs = 0;
  95
  96         /* Find the __bug_table section, if present */
  97         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  98         for (i = 1; i < hdr->e_shnum; i++) {
  99                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
 100                         continue;
 101                 mod->bug_table = (void *) sechdrs[i].sh_addr;
 102                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
 103                 break;
 104         }
 105
 106         /*
 107          * Strictly speaking this should have a spinlock to protect against
 108          * traversals, but since we only traverse on BUG()s, a spinlock
 109          * could potentially lead to deadlock and thus be counter-productive.
 110          * Thus, this uses RCU to safely manipulate the bug list, since BUG
 111          * must run in non-interruptive state.
 112          */
 113         list_add_rcu(&mod->bug_list, &module_bug_list);
 114 }
 115
 116 void module_bug_cleanup(struct module *mod)
 117 {
 118         lockdep_assert_held(&module_mutex);
 119         list_del_rcu(&mod->bug_list);
 120 }
 121
 122 #else
 123
 124 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
 125 {
 126         return NULL;
 127 }
 128 #endif
 129
 130 const struct bug_entry *find_bug(unsigned long bugaddr)
 131 {
 132         const struct bug_entry *bug;
 133
 134         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 135                 if (bugaddr == bug_addr(bug))
 136                         return bug;
 137
 138         return module_find_bug(bugaddr);
 139 }
 140
 141 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 142 {
 143         const struct bug_entry *bug;
 144         const char *file;
 145         unsigned line, warning;
 146
 147         if (!is_valid_bugaddr(bugaddr))
 148                 return BUG_TRAP_TYPE_NONE;
 149
 150         bug = find_bug(bugaddr);
 151
 152         file = NULL;
 153         line = 0;
 154         warning = 0;
 155
 156         if (bug) {
 157 #ifdef CONFIG_DEBUG_BUGVERBOSE
 158 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 159                 file = bug->file;
 160 #else
 161                 file = (const char *)bug + bug->file_disp;
 162 #endif
 163                 line = bug->line;
 164 #endif
 165                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 166         }
 167
 168         if (warning) {
 169                 /* this is a WARN_ON rather than BUG/BUG_ON */
 170                 pr_warn("------------[ cut here ]------------\n");
 171
 172                 if (file)
 173                         pr_warn("WARNING: at %s:%u\n", file, line);
 174                 else
 175                         pr_warn("WARNING: at %p [verbose debug info unavailable]\n",
 176                                 (void *)bugaddr);
 177
 178                 print_modules();
 179                 show_regs(regs);
 180                 print_oops_end_marker();
 181                 /* Just a warning, don't kill lockdep. */
 182                 add_taint(BUG_GET_TAINT(bug), LOCKDEP_STILL_OK);
 183                 return BUG_TRAP_TYPE_WARN;
 184         }
 185
 186         printk(KERN_DEFAULT "------------[ cut here ]------------\n");
 187
 188         if (file)
 189                 pr_crit("kernel BUG at %s:%u!\n", file, line);
 190         else
 191                 pr_crit("Kernel BUG at %p [verbose debug info unavailable]\n",
 192                         (void *)bugaddr);
 193
 194         return BUG_TRAP_TYPE_BUG;
 195 }