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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>4 */5 6/*7 * This file reads all the special sections which have alternate instructions8 * 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 20struct 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 29static 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 57void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt)58{59}60 61static 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(reloc);66}67 68static 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 orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig);88 if (!orig_reloc) {89 WARN_FUNC("can't find orig reloc", sec, offset + entry->orig);90 return -1;91 }92 93 reloc_to_sec_off(orig_reloc, &alt->orig_sec, &alt->orig_off);94 95 if (entry->feature) {96 unsigned short feature;97 98 feature = bswap_if_needed(elf,99 *(unsigned short *)(sec->data->d_buf +100 offset +101 entry->feature));102 arch_handle_alternative(feature, alt);103 }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 = reloc_addend(key_reloc);130 }131 132 return 0;133}134 135/*136 * Read all the special sections and create a list of special_alt structs which137 * describe all the alternate instructions which can be patched in or138 * redirected to at runtime.139 */140int 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}183