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 #include <linux/rculist.h>
  49
  50 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
  51
  52 static inline unsigned long bug_addr(const struct bug_entry *bug)
  53 {
  54 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
  55         return bug->bug_addr;
  56 #else
  57         return (unsigned long)bug + bug->bug_addr_disp;
  58 #endif
  59 }
  60
  61 #ifdef CONFIG_MODULES
  62 /* Updates are protected by module mutex */
  63 static LIST_HEAD(module_bug_list);
  64
  65 static struct bug_entry *module_find_bug(unsigned long bugaddr)
  66 {
  67         struct module *mod;
  68         struct bug_entry *bug = NULL;
  69
  70         rcu_read_lock_sched();
  71         list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
  72                 unsigned i;
  73
  74                 bug = mod->bug_table;
  75                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
  76                         if (bugaddr == bug_addr(bug))
  77                                 goto out;
  78         }
  79         bug = NULL;
  80 out:
  81         rcu_read_unlock_sched();
  82
  83         return bug;
  84 }
  85
  86 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  87                          struct module *mod)
  88 {
  89         char *secstrings;
  90         unsigned int i;
  91
  92         lockdep_assert_held(&module_mutex);
  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         lockdep_assert_held(&module_mutex);
 120         list_del_rcu(&mod->bug_list);
 121 }
 122
 123 #else
 124
 125 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
 126 {
 127         return NULL;
 128 }
 129 #endif
 130
 131 struct bug_entry *find_bug(unsigned long bugaddr)
 132 {
 133         struct bug_entry *bug;
 134
 135         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 136                 if (bugaddr == bug_addr(bug))
 137                         return bug;
 138
 139         return module_find_bug(bugaddr);
 140 }
 141
 142 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 143 {
 144         struct bug_entry *bug;
 145         const char *file;
 146         unsigned line, warning, once, done;
 147
 148         if (!is_valid_bugaddr(bugaddr))
 149                 return BUG_TRAP_TYPE_NONE;
 150
 151         bug = find_bug(bugaddr);
 152
 153         file = NULL;
 154         line = 0;
 155         warning = 0;
 156
 157         if (bug) {
 158 #ifdef CONFIG_DEBUG_BUGVERBOSE
 159 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 160                 file = bug->file;
 161 #else
 162                 file = (const char *)bug + bug->file_disp;
 163 #endif
 164                 line = bug->line;
 165 #endif
 166                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 167                 once = (bug->flags & BUGFLAG_ONCE) != 0;
 168                 done = (bug->flags & BUGFLAG_DONE) != 0;
 169
 170                 if (warning && once) {
 171                         if (done)
 172                                 return BUG_TRAP_TYPE_WARN;
 173
 174                         /*
 175                          * Since this is the only store, concurrency is not an issue.
 176                          */
 177                         bug->flags |= BUGFLAG_DONE;
 178                 }
 179         }
 180
 181         if (warning) {
 182                 /* this is a WARN_ON rather than BUG/BUG_ON */
 183                 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
 184                        NULL);
 185                 return BUG_TRAP_TYPE_WARN;
 186         }
 187
 188         printk(KERN_DEFAULT "------------[ cut here ]------------\n");
 189
 190         if (file)
 191                 pr_crit("kernel BUG at %s:%u!\n", file, line);
 192         else
 193                 pr_crit("Kernel BUG at %p [verbose debug info unavailable]\n",
 194                         (void *)bugaddr);
 195
 196         return BUG_TRAP_TYPE_BUG;
 197 }