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
  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 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
  56         return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;
  57 #else
  58         return bug->bug_addr;
  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         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         list_del_rcu(&mod->bug_list);
 119 }
 120
 121 #else
 122
 123 static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
 124 {
 125         return NULL;
 126 }
 127 #endif
 128
 129 void bug_get_file_line(struct bug_entry *bug, const char **file,
 130                        unsigned int *line)
 131 {
 132 #ifdef CONFIG_DEBUG_BUGVERBOSE
 133 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 134         *file = (const char *)&bug->file_disp + bug->file_disp;
 135 #else
 136         *file = bug->file;
 137 #endif
 138         *line = bug->line;
 139 #else
 140         *file = NULL;
 141         *line = 0;
 142 #endif
 143 }
 144
 145 struct bug_entry *find_bug(unsigned long bugaddr)
 146 {
 147         struct bug_entry *bug;
 148
 149         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 150                 if (bugaddr == bug_addr(bug))
 151                         return bug;
 152
 153         return module_find_bug(bugaddr);
 154 }
 155
 156 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 157 {
 158         struct bug_entry *bug;
 159         const char *file;
 160         unsigned line, warning, once, done;
 161
 162         if (!is_valid_bugaddr(bugaddr))
 163                 return BUG_TRAP_TYPE_NONE;
 164
 165         bug = find_bug(bugaddr);
 166         if (!bug)
 167                 return BUG_TRAP_TYPE_NONE;
 168
 169         disable_trace_on_warning();
 170
 171         bug_get_file_line(bug, &file, &line);
 172
 173         warning = (bug->flags & BUGFLAG_WARNING) != 0;
 174         once = (bug->flags & BUGFLAG_ONCE) != 0;
 175         done = (bug->flags & BUGFLAG_DONE) != 0;
 176
 177         if (warning && once) {
 178                 if (done)
 179                         return BUG_TRAP_TYPE_WARN;
 180
 181                 /*
 182                  * Since this is the only store, concurrency is not an issue.
 183                  */
 184                 bug->flags |= BUGFLAG_DONE;
 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 }