lib/extable.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Derived from arch/ppc/mm/extable.c and arch/i386/mm/extable.c.
   4  *
   5  * Copyright (C) 2004 Paul Mackerras, IBM Corp.
   6  */
   7
   8 #include <linux/bsearch.h>
   9 #include <linux/module.h>
  10 #include <linux/init.h>
  11 #include <linux/sort.h>
  12 #include <linux/uaccess.h>
  13 #include <linux/extable.h>
  14
  15 #ifndef ARCH_HAS_RELATIVE_EXTABLE
  16 #define ex_to_insn(x)   ((x)->insn)
  17 #else
  18 static inline unsigned long ex_to_insn(const struct exception_table_entry *x)
  19 {
  20         return (unsigned long)&x->insn + x->insn;
  21 }
  22 #endif
  23
  24 #ifndef ARCH_HAS_RELATIVE_EXTABLE
  25 #define swap_ex         NULL
  26 #else
  27 static void swap_ex(void *a, void *b, int size)
  28 {
  29         struct exception_table_entry *x = a, *y = b, tmp;
  30         int delta = b - a;
  31
  32         tmp = *x;
  33         x->insn = y->insn + delta;
  34         y->insn = tmp.insn - delta;
  35
  36 #ifdef swap_ex_entry_fixup
  37         swap_ex_entry_fixup(x, y, tmp, delta);
  38 #else
  39         x->fixup = y->fixup + delta;
  40         y->fixup = tmp.fixup - delta;
  41 #endif
  42 }
  43 #endif /* ARCH_HAS_RELATIVE_EXTABLE */
  44
  45 /*
  46  * The exception table needs to be sorted so that the binary
  47  * search that we use to find entries in it works properly.
  48  * This is used both for the kernel exception table and for
  49  * the exception tables of modules that get loaded.
  50  */
  51 static int cmp_ex_sort(const void *a, const void *b)
  52 {
  53         const struct exception_table_entry *x = a, *y = b;
  54
  55         /* avoid overflow */
  56         if (ex_to_insn(x) > ex_to_insn(y))
  57                 return 1;
  58         if (ex_to_insn(x) < ex_to_insn(y))
  59                 return -1;
  60         return 0;
  61 }
  62
  63 void sort_extable(struct exception_table_entry *start,
  64                   struct exception_table_entry *finish)
  65 {
  66         sort(start, finish - start, sizeof(struct exception_table_entry),
  67              cmp_ex_sort, swap_ex);
  68 }
  69
  70 #ifdef CONFIG_MODULES
  71 /*
  72  * If the exception table is sorted, any referring to the module init
  73  * will be at the beginning or the end.
  74  */
  75 void trim_init_extable(struct module *m)
  76 {
  77         /*trim the beginning*/
  78         while (m->num_exentries &&
  79                within_module_init(ex_to_insn(&m->extable[0]), m)) {
  80                 m->extable++;
  81                 m->num_exentries--;
  82         }
  83         /*trim the end*/
  84         while (m->num_exentries &&
  85                within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]),
  86                                   m))
  87                 m->num_exentries--;
  88 }
  89 #endif /* CONFIG_MODULES */
  90
  91 static int cmp_ex_search(const void *key, const void *elt)
  92 {
  93         const struct exception_table_entry *_elt = elt;
  94         unsigned long _key = *(unsigned long *)key;
  95
  96         /* avoid overflow */
  97         if (_key > ex_to_insn(_elt))
  98                 return 1;
  99         if (_key < ex_to_insn(_elt))
 100                 return -1;
 101         return 0;
 102 }
 103
 104 /*
 105  * Search one exception table for an entry corresponding to the
 106  * given instruction address, and return the address of the entry,
 107  * or NULL if none is found.
 108  * We use a binary search, and thus we assume that the table is
 109  * already sorted.
 110  */
 111 const struct exception_table_entry *
 112 search_extable(const struct exception_table_entry *base,
 113                const size_t num,
 114                unsigned long value)
 115 {
 116         return bsearch(&value, base, num,
 117                        sizeof(struct exception_table_entry), cmp_ex_search);
 118 }