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189 lines
4.3 KiB
189 lines
4.3 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* Copyright (C) 2015 Josh Poimboeuf <[email protected]> |
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*/ |
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/* |
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* This file reads all the special sections which have alternate instructions |
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* which can be patched in or redirected to at runtime. |
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*/ |
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#include <stdlib.h> |
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#include <string.h> |
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#include <arch/special.h> |
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#include <objtool/builtin.h> |
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#include <objtool/special.h> |
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#include <objtool/warn.h> |
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#include <objtool/endianness.h> |
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struct special_entry { |
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const char *sec; |
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bool group, jump_or_nop; |
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unsigned char size, orig, new; |
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unsigned char orig_len, new_len; /* group only */ |
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unsigned char feature; /* ALTERNATIVE macro CPU feature */ |
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unsigned char key; /* jump_label key */ |
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}; |
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struct special_entry entries[] = { |
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{ |
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.sec = ".altinstructions", |
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.group = true, |
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.size = ALT_ENTRY_SIZE, |
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.orig = ALT_ORIG_OFFSET, |
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.orig_len = ALT_ORIG_LEN_OFFSET, |
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.new = ALT_NEW_OFFSET, |
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.new_len = ALT_NEW_LEN_OFFSET, |
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.feature = ALT_FEATURE_OFFSET, |
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}, |
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{ |
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.sec = "__jump_table", |
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.jump_or_nop = true, |
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.size = JUMP_ENTRY_SIZE, |
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.orig = JUMP_ORIG_OFFSET, |
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.new = JUMP_NEW_OFFSET, |
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.key = JUMP_KEY_OFFSET, |
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}, |
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{ |
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.sec = "__ex_table", |
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.size = EX_ENTRY_SIZE, |
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.orig = EX_ORIG_OFFSET, |
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.new = EX_NEW_OFFSET, |
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}, |
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{}, |
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}; |
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void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt) |
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{ |
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} |
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static void reloc_to_sec_off(struct reloc *reloc, struct section **sec, |
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unsigned long *off) |
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{ |
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*sec = reloc->sym->sec; |
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*off = reloc->sym->offset + reloc->addend; |
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} |
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static int get_alt_entry(struct elf *elf, struct special_entry *entry, |
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struct section *sec, int idx, |
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struct special_alt *alt) |
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{ |
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struct reloc *orig_reloc, *new_reloc; |
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unsigned long offset; |
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offset = idx * entry->size; |
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alt->group = entry->group; |
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alt->jump_or_nop = entry->jump_or_nop; |
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if (alt->group) { |
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alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset + |
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entry->orig_len); |
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alt->new_len = *(unsigned char *)(sec->data->d_buf + offset + |
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entry->new_len); |
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} |
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if (entry->feature) { |
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unsigned short feature; |
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feature = bswap_if_needed(*(unsigned short *)(sec->data->d_buf + |
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offset + |
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entry->feature)); |
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arch_handle_alternative(feature, alt); |
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} |
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orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig); |
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if (!orig_reloc) { |
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WARN_FUNC("can't find orig reloc", sec, offset + entry->orig); |
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return -1; |
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} |
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reloc_to_sec_off(orig_reloc, &alt->orig_sec, &alt->orig_off); |
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if (!entry->group || alt->new_len) { |
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new_reloc = find_reloc_by_dest(elf, sec, offset + entry->new); |
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if (!new_reloc) { |
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WARN_FUNC("can't find new reloc", |
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sec, offset + entry->new); |
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return -1; |
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} |
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/* |
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* Skip retpoline .altinstr_replacement... we already rewrite the |
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* instructions for retpolines anyway, see arch_is_retpoline() |
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* usage in add_{call,jump}_destinations(). |
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*/ |
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if (arch_is_retpoline(new_reloc->sym)) |
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return 1; |
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reloc_to_sec_off(new_reloc, &alt->new_sec, &alt->new_off); |
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/* _ASM_EXTABLE_EX hack */ |
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if (alt->new_off >= 0x7ffffff0) |
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alt->new_off -= 0x7ffffff0; |
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} |
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if (entry->key) { |
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struct reloc *key_reloc; |
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key_reloc = find_reloc_by_dest(elf, sec, offset + entry->key); |
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if (!key_reloc) { |
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WARN_FUNC("can't find key reloc", |
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sec, offset + entry->key); |
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return -1; |
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} |
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alt->key_addend = key_reloc->addend; |
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} |
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return 0; |
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} |
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/* |
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* Read all the special sections and create a list of special_alt structs which |
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* describe all the alternate instructions which can be patched in or |
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* redirected to at runtime. |
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*/ |
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int special_get_alts(struct elf *elf, struct list_head *alts) |
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{ |
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struct special_entry *entry; |
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struct section *sec; |
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unsigned int nr_entries; |
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struct special_alt *alt; |
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int idx, ret; |
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INIT_LIST_HEAD(alts); |
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for (entry = entries; entry->sec; entry++) { |
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sec = find_section_by_name(elf, entry->sec); |
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if (!sec) |
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continue; |
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if (sec->sh.sh_size % entry->size != 0) { |
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WARN("%s size not a multiple of %d", |
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sec->name, entry->size); |
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return -1; |
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} |
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nr_entries = sec->sh.sh_size / entry->size; |
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for (idx = 0; idx < nr_entries; idx++) { |
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alt = malloc(sizeof(*alt)); |
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if (!alt) { |
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WARN("malloc failed"); |
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return -1; |
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} |
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memset(alt, 0, sizeof(*alt)); |
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ret = get_alt_entry(elf, entry, sec, idx, alt); |
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if (ret > 0) |
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continue; |
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if (ret < 0) |
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return ret; |
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list_add_tail(&alt->list, alts); |
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} |
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} |
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return 0; |
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}
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