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 #include <linux/ftrace.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 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
  57         return bug->bug_addr;
  58 #else
  59         return (unsigned long)bug + bug->bug_addr_disp;
  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         lockdep_assert_held(&module_mutex);
  95
  96         mod->bug_table = NULL;
  97         mod->num_bugs = 0;
  98
  99         /* Find the __bug_table section, if present */
 100         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
 101         for (i = 1; i < hdr->e_shnum; i++) {
 102                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
 103                         continue;
 104                 mod->bug_table = (void *) sechdrs[i].sh_addr;
 105                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
 106                 break;
 107         }
 108
 109         /*
 110          * Strictly speaking this should have a spinlock to protect against
 111          * traversals, but since we only traverse on BUG()s, a spinlock
 112          * could potentially lead to deadlock and thus be counter-productive.
 113          * Thus, this uses RCU to safely manipulate the bug list, since BUG
 114          * must run in non-interruptive state.
 115          */
 116         list_add_rcu(&mod->bug_list, &module_bug_list);
 117 }
 118
 119 void module_bug_cleanup(struct module *mod)
 120 {
 121         lockdep_assert_held(&module_mutex);
 122         list_del_rcu(&mod->bug_list);
 123 }
 124
 125 #else
 126
 127 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
 128 {
 129         return NULL;
 130 }
 131 #endif
 132
 133 struct bug_entry *find_bug(unsigned long bugaddr)
 134 {
 135         struct bug_entry *bug;
 136
 137         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 138                 if (bugaddr == bug_addr(bug))
 139                         return bug;
 140
 141         return module_find_bug(bugaddr);
 142 }
 143
 144 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 145 {
 146         struct bug_entry *bug;
 147         const char *file;
 148         unsigned line, warning, once, done;
 149
 150         if (!is_valid_bugaddr(bugaddr))
 151                 return BUG_TRAP_TYPE_NONE;
 152
 153         bug = find_bug(bugaddr);
 154         if (!bug)
 155                 return BUG_TRAP_TYPE_NONE;
 156
 157         disable_trace_on_warning();
 158
 159         file = NULL;
 160         line = 0;
 161         warning = 0;
 162
 163         if (bug) {
 164 #ifdef CONFIG_DEBUG_BUGVERBOSE
 165 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 166                 file = bug->file;
 167 #else
 168                 file = (const char *)bug + bug->file_disp;
 169 #endif
 170                 line = bug->line;
 171 #endif
 172                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 173                 once = (bug->flags & BUGFLAG_ONCE) != 0;
 174                 done = (bug->flags & BUGFLAG_DONE) != 0;
 175
 176                 if (warning && once) {
 177                         if (done)
 178                                 return BUG_TRAP_TYPE_WARN;
 179
 180                         /*
 181                          * Since this is the only store, concurrency is not an issue.
 182                          */
 183                         bug->flags |= BUGFLAG_DONE;
 184                 }
 185         }
 186
 187         /*
 188          * BUG() and WARN_ON() families don't print a custom debug message
 189          * before triggering the exception handler, so we must add the
 190          * "cut here" line now. WARN() issues its own "cut here" before the
 191          * extra debugging message it writes before triggering the handler.
 192          */
 193         if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
 194                 printk(KERN_DEFAULT CUT_HERE);
 195
 196         if (warning) {
 197                 /* this is a WARN_ON rather than BUG/BUG_ON */
 198                 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
 199                        NULL);
 200                 return BUG_TRAP_TYPE_WARN;
 201         }
 202
 203         if (file)
 204                 pr_crit("kernel BUG at %s:%u!\n", file, line);
 205         else
 206                 pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
 207                         (void *)bugaddr);
 208
 209         return BUG_TRAP_TYPE_BUG;
 210 }
 211
 212 static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
 213 {
 214         struct bug_entry *bug;
 215
 216         for (bug = start; bug < end; bug++)
 217                 bug->flags &= ~BUGFLAG_DONE;
 218 }
 219
 220 void generic_bug_clear_once(void)
 221 {
 222 #ifdef CONFIG_MODULES
 223         struct module *mod;
 224
 225         rcu_read_lock_sched();
 226         list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
 227                 clear_once_table(mod->bug_table,
 228                                  mod->bug_table + mod->num_bugs);
 229         rcu_read_unlock_sched();
 230 #endif
 231
 232         clear_once_table(__start___bug_table, __stop___bug_table);
 233 }