tools/objtool/special.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
   4  */
   5
   6 /*
   7  * This file reads all the special sections which have alternate instructions
   8  * which can be patched in or redirected to at runtime.
   9  */
  10
  11 #include <stdlib.h>
  12 #include <string.h>
  13
  14 #include <arch/special.h>
  15 #include <objtool/builtin.h>
  16 #include <objtool/special.h>
  17 #include <objtool/warn.h>
  18 #include <objtool/endianness.h>
  19
  20 struct special_entry {
  21         const char *sec;
  22         bool group, jump_or_nop;
  23         unsigned char size, orig, new;
  24         unsigned char orig_len, new_len; /* group only */
  25         unsigned char feature; /* ALTERNATIVE macro CPU feature */
  26         unsigned char key; /* jump_label key */
  27 };
  28
  29 static const struct special_entry entries[] = {
  30         {
  31                 .sec = ".altinstructions",
  32                 .group = true,
  33                 .size = ALT_ENTRY_SIZE,
  34                 .orig = ALT_ORIG_OFFSET,
  35                 .orig_len = ALT_ORIG_LEN_OFFSET,
  36                 .new = ALT_NEW_OFFSET,
  37                 .new_len = ALT_NEW_LEN_OFFSET,
  38                 .feature = ALT_FEATURE_OFFSET,
  39         },
  40         {
  41                 .sec = "__jump_table",
  42                 .jump_or_nop = true,
  43                 .size = JUMP_ENTRY_SIZE,
  44                 .orig = JUMP_ORIG_OFFSET,
  45                 .new = JUMP_NEW_OFFSET,
  46                 .key = JUMP_KEY_OFFSET,
  47         },
  48         {
  49                 .sec = "__ex_table",
  50                 .size = EX_ENTRY_SIZE,
  51                 .orig = EX_ORIG_OFFSET,
  52                 .new = EX_NEW_OFFSET,
  53         },
  54         {},
  55 };
  56
  57 void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt)
  58 {
  59 }
  60
  61 static void reloc_to_sec_off(struct reloc *reloc, struct section **sec,
  62                              unsigned long *off)
  63 {
  64         *sec = reloc->sym->sec;
  65         *off = reloc->sym->offset + reloc->addend;
  66 }
  67
  68 static int get_alt_entry(struct elf *elf, const struct special_entry *entry,
  69                          struct section *sec, int idx,
  70                          struct special_alt *alt)
  71 {
  72         struct reloc *orig_reloc, *new_reloc;
  73         unsigned long offset;
  74
  75         offset = idx * entry->size;
  76
  77         alt->group = entry->group;
  78         alt->jump_or_nop = entry->jump_or_nop;
  79
  80         if (alt->group) {
  81                 alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset +
  82                                                    entry->orig_len);
  83                 alt->new_len = *(unsigned char *)(sec->data->d_buf + offset +
  84                                                   entry->new_len);
  85         }
  86
  87         if (entry->feature) {
  88                 unsigned short feature;
  89
  90                 feature = bswap_if_needed(elf,
  91                                           *(unsigned short *)(sec->data->d_buf +
  92                                                               offset +
  93                                                               entry->feature));
  94                 arch_handle_alternative(feature, alt);
  95         }
  96
  97         orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig);
  98         if (!orig_reloc) {
  99                 WARN_FUNC("can't find orig reloc", sec, offset + entry->orig);
 100                 return -1;
 101         }
 102
 103         reloc_to_sec_off(orig_reloc, &alt->orig_sec, &alt->orig_off);
 104
 105         if (!entry->group || alt->new_len) {
 106                 new_reloc = find_reloc_by_dest(elf, sec, offset + entry->new);
 107                 if (!new_reloc) {
 108                         WARN_FUNC("can't find new reloc",
 109                                   sec, offset + entry->new);
 110                         return -1;
 111                 }
 112
 113                 reloc_to_sec_off(new_reloc, &alt->new_sec, &alt->new_off);
 114
 115                 /* _ASM_EXTABLE_EX hack */
 116                 if (alt->new_off >= 0x7ffffff0)
 117                         alt->new_off -= 0x7ffffff0;
 118         }
 119
 120         if (entry->key) {
 121                 struct reloc *key_reloc;
 122
 123                 key_reloc = find_reloc_by_dest(elf, sec, offset + entry->key);
 124                 if (!key_reloc) {
 125                         WARN_FUNC("can't find key reloc",
 126                                   sec, offset + entry->key);
 127                         return -1;
 128                 }
 129                 alt->key_addend = key_reloc->addend;
 130         }
 131
 132         return 0;
 133 }
 134
 135 /*
 136  * Read all the special sections and create a list of special_alt structs which
 137  * describe all the alternate instructions which can be patched in or
 138  * redirected to at runtime.
 139  */
 140 int special_get_alts(struct elf *elf, struct list_head *alts)
 141 {
 142         const struct special_entry *entry;
 143         struct section *sec;
 144         unsigned int nr_entries;
 145         struct special_alt *alt;
 146         int idx, ret;
 147
 148         INIT_LIST_HEAD(alts);
 149
 150         for (entry = entries; entry->sec; entry++) {
 151                 sec = find_section_by_name(elf, entry->sec);
 152                 if (!sec)
 153                         continue;
 154
 155                 if (sec->sh.sh_size % entry->size != 0) {
 156                         WARN("%s size not a multiple of %d",
 157                              sec->name, entry->size);
 158                         return -1;
 159                 }
 160
 161                 nr_entries = sec->sh.sh_size / entry->size;
 162
 163                 for (idx = 0; idx < nr_entries; idx++) {
 164                         alt = malloc(sizeof(*alt));
 165                         if (!alt) {
 166                                 WARN("malloc failed");
 167                                 return -1;
 168                         }
 169                         memset(alt, 0, sizeof(*alt));
 170
 171                         ret = get_alt_entry(elf, entry, sec, idx, alt);
 172                         if (ret > 0)
 173                                 continue;
 174                         if (ret < 0)
 175                                 return ret;
 176
 177                         list_add_tail(&alt->list, alts);
 178                 }
 179         }
 180
 181         return 0;
 182 }