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 19 struct special_entry { 20 const char *sec; 21 bool group, jump_or_nop; 22 unsigned char size, orig, new; 23 unsigned char orig_len, new_len; /* group only */ 24 unsigned char feature; /* ALTERNATIVE macro CPU feature */ 25 unsigned char key; /* jump_label key */ 26 }; 27 28 static const struct special_entry entries[] = { 29 { 30 .sec = ".altinstructions", 31 .group = true, 32 .size = ALT_ENTRY_SIZE, 33 .orig = ALT_ORIG_OFFSET, 34 .orig_len = ALT_ORIG_LEN_OFFSET, 35 .new = ALT_NEW_OFFSET, 36 .new_len = ALT_NEW_LEN_OFFSET, 37 .feature = ALT_FEATURE_OFFSET, 38 }, 39 { 40 .sec = "__jump_table", 41 .jump_or_nop = true, 42 .size = JUMP_ENTRY_SIZE, 43 .orig = JUMP_ORIG_OFFSET, 44 .new = JUMP_NEW_OFFSET, 45 .key = JUMP_KEY_OFFSET, 46 }, 47 { 48 .sec = "__ex_table", 49 .size = EX_ENTRY_SIZE, 50 .orig = EX_ORIG_OFFSET, 51 .new = EX_NEW_OFFSET, 52 }, 53 {}, 54 }; 55 56 void __weak arch_handle_alternative(struct special_alt *alt) 57 { 58 } 59 60 static void reloc_to_sec_off(struct reloc *reloc, struct section **sec, 61 unsigned long *off) 62 { 63 *sec = reloc->sym->sec; 64 *off = reloc->sym->offset + reloc_addend(reloc); 65 } 66 67 static int get_alt_entry(struct elf *elf, const struct special_entry *entry, 68 struct section *sec, int idx, 69 struct special_alt *alt) 70 { 71 struct reloc *orig_reloc, *new_reloc; 72 unsigned long offset; 73 74 offset = idx * entry->size; 75 76 alt->group = entry->group; 77 alt->jump_or_nop = entry->jump_or_nop; 78 79 if (alt->group) { 80 alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset + 81 entry->orig_len); 82 alt->new_len = *(unsigned char *)(sec->data->d_buf + offset + 83 entry->new_len); 84 } 85 86 orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig); 87 if (!orig_reloc) { 88 ERROR_FUNC(sec, offset + entry->orig, "can't find orig reloc"); 89 return -1; 90 } 91 92 reloc_to_sec_off(orig_reloc, &alt->orig_sec, &alt->orig_off); 93 94 arch_handle_alternative(alt); 95 96 if (!entry->group || alt->new_len) { 97 new_reloc = find_reloc_by_dest(elf, sec, offset + entry->new); 98 if (!new_reloc) { 99 ERROR_FUNC(sec, offset + entry->new, "can't find new reloc"); 100 return -1; 101 } 102 103 reloc_to_sec_off(new_reloc, &alt->new_sec, &alt->new_off); 104 105 /* _ASM_EXTABLE_EX hack */ 106 if (alt->new_off >= 0x7ffffff0) 107 alt->new_off -= 0x7ffffff0; 108 } 109 110 if (entry->key) { 111 struct reloc *key_reloc; 112 113 key_reloc = find_reloc_by_dest(elf, sec, offset + entry->key); 114 if (!key_reloc) { 115 ERROR_FUNC(sec, offset + entry->key, "can't find key reloc"); 116 return -1; 117 } 118 alt->key_addend = reloc_addend(key_reloc); 119 } 120 121 return 0; 122 } 123 124 /* 125 * Read all the special sections and create a list of special_alt structs which 126 * describe all the alternate instructions which can be patched in or 127 * redirected to at runtime. 128 */ 129 int special_get_alts(struct elf *elf, struct list_head *alts) 130 { 131 const struct special_entry *entry; 132 struct section *sec; 133 unsigned int nr_entries; 134 struct special_alt *alt; 135 int idx; 136 137 INIT_LIST_HEAD(alts); 138 139 for (entry = entries; entry->sec; entry++) { 140 sec = find_section_by_name(elf, entry->sec); 141 if (!sec) 142 continue; 143 144 if (sec_size(sec) % entry->size != 0) { 145 ERROR("%s size not a multiple of %d", sec->name, entry->size); 146 return -1; 147 } 148 149 nr_entries = sec_size(sec) / entry->size; 150 151 for (idx = 0; idx < nr_entries; idx++) { 152 alt = malloc(sizeof(*alt)); 153 if (!alt) { 154 ERROR_GLIBC("malloc failed"); 155 return -1; 156 } 157 memset(alt, 0, sizeof(*alt)); 158 159 if (get_alt_entry(elf, entry, sec, idx, alt)) 160 return -1; 161 162 list_add_tail(&alt->list, alts); 163 } 164 } 165 166 return 0; 167 } 168