Quelle bug.c Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
  Generic support for BUG()

  This respects the following config options:

  CONFIG_BUG - emit BUG traps.  Nothing happens without this.
  CONFIG_GENERIC_BUG - enable this code.
  CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit relative pointers for bug_addr and file
  CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG

  CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
  (though they're generally always on).

  CONFIG_GENERIC_BUG is set by each architecture using this code.

  To use this, your architecture must:

  1. Set up the config options:
     - Enable CONFIG_GENERIC_BUG if CONFIG_BUG

  2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)
     - Define HAVE_ARCH_BUG
     - Implement BUG() to generate a faulting instruction
     - NOTE: struct bug_entry does not have "file" or "line" entries
       when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
       the values accordingly.

  3. Implement the trap
     - In the illegal instruction trap handler (typically), verify
       that the fault was in kernel mode, and call report_bug()
     - report_bug() will return whether it was a false alarm, a warning,
       or an actual bug.
     - You must implement the is_valid_bugaddr(bugaddr) callback which
       returns true if the eip is a real kernel address, and it points
       to the expected BUG trap instruction.

    Jeremy Fitzhardinge <jeremy@goop.org> 2006
*/

#define pr_fmt(fmt) fmt

#include <linux/list.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bug.h>
#include <linux/sched.h>
#include <linux/rculist.h>
#include <linux/ftrace.h>
#include <linux/context_tracking.h>

extern struct bug_entry __start___bug_table[], __stop___bug_table[];

static inline unsigned long bug_addr(const struct bug_entry *bug)
{
#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;
#else
return bug->bug_addr;
#endif
}

#ifdef CONFIG_MODULES
/* Updates are protected by module mutex */
static LIST_HEAD(module_bug_list);

static struct bug_entry *module_find_bug(unsigned long bugaddr)
{
struct bug_entry *bug;
struct module *mod;

guard(rcu)();
list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
  unsigned i;

  bug = mod->bug_table;
  for (i = 0; i < mod->num_bugs; ++i, ++bug)
   if (bugaddr == bug_addr(bug))
    return bug;
}
return NULL;
}

void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
    struct module *mod)
{
char *secstrings;
unsigned int i;

mod->bug_table = NULL;
mod->num_bugs = 0;

/* Find the __bug_table section, if present */
secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
for (i = 1; i < hdr->e_shnum; i++) {
  if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
   continue;
  mod->bug_table = (void *) sechdrs[i].sh_addr;
  mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
  break;
}

/*
* Strictly speaking this should have a spinlock to protect against
* traversals, but since we only traverse on BUG()s, a spinlock
* could potentially lead to deadlock and thus be counter-productive.
* Thus, this uses RCU to safely manipulate the bug list, since BUG
* must run in non-interruptive state.
*/
list_add_rcu(&mod->bug_list, &module_bug_list);
}

void module_bug_cleanup(struct module *mod)
{
list_del_rcu(&mod->bug_list);
}

#else

static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
{
return NULL;
}
#endif

void bug_get_file_line(struct bug_entry *bug, const char **file,
         unsigned int *line)
{
#ifdef CONFIG_DEBUG_BUGVERBOSE
#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
*file = (const char *)&bug->file_disp + bug->file_disp;
#else
*file = bug->file;
#endif
*line = bug->line;
#else
*file = NULL;
*line = 0;
#endif
}

struct bug_entry *find_bug(unsigned long bugaddr)
{
struct bug_entry *bug;

for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
  if (bugaddr == bug_addr(bug))
   return bug;

return module_find_bug(bugaddr);
}

static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
{
struct bug_entry *bug;
const char *file;
unsigned line, warning, once, done;

if (!is_valid_bugaddr(bugaddr))
  return BUG_TRAP_TYPE_NONE;

bug = find_bug(bugaddr);
if (!bug)
  return BUG_TRAP_TYPE_NONE;

disable_trace_on_warning();

bug_get_file_line(bug, &file, &line);

warning = (bug->flags & BUGFLAG_WARNING) != 0;
once = (bug->flags & BUGFLAG_ONCE) != 0;
done = (bug->flags & BUGFLAG_DONE) != 0;

if (warning && once) {
  if (done)
   return BUG_TRAP_TYPE_WARN;

  /*
* Since this is the only store, concurrency is not an issue.
*/
  bug->flags |= BUGFLAG_DONE;
}

/*
* BUG() and WARN_ON() families don't print a custom debug message
* before triggering the exception handler, so we must add the
* "cut here" line now. WARN() issues its own "cut here" before the
* extra debugging message it writes before triggering the handler.
*/
if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
  printk(KERN_DEFAULT CUT_HERE);

if (warning) {
  /* this is a WARN_ON rather than BUG/BUG_ON */
  __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
         NULL);
  return BUG_TRAP_TYPE_WARN;
}

if (file)
  pr_crit("kernel BUG at %s:%u!\n", file, line);
else
  pr_crit("Kernel BUG at %pB [verbose debug info unavailable]\n",
   (void *)bugaddr);

return BUG_TRAP_TYPE_BUG;
}

enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
{
enum bug_trap_type ret;
bool rcu = false;

rcu = warn_rcu_enter();
ret = __report_bug(bugaddr, regs);
warn_rcu_exit(rcu);

return ret;
}

static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
{
struct bug_entry *bug;

for (bug = start; bug < end; bug++)
  bug->flags &= ~BUGFLAG_DONE;
}

void generic_bug_clear_once(void)
{
#ifdef CONFIG_MODULES
struct module *mod;

scoped_guard(rcu) {
  list_for_each_entry_rcu(mod, &module_bug_list, bug_list)
   clear_once_table(mod->bug_table,
      mod->bug_table + mod->num_bugs);
}
#endif

clear_once_table(__start___bug_table, __stop___bug_table);
}

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