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134ab5bd18
Instead of writing complete alternatives, simply provide a list of all the retpoline thunk calls. Then the kernel is free to do with them as it pleases. Simpler code all-round. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Borislav Petkov <bp@suse.de> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Tested-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/r/20211026120309.850007165@infradead.org
182 lines
4.0 KiB
C
182 lines
4.0 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
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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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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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