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