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![Josh Poimboeuf](/assets/img/avatar_default.png)
This is a major rewrite of objtool. Instead of only tracking frame pointer changes, it now tracks all stack-related operations, including all register saves/restores. In addition to making stack validation more robust, this also paves the way for undwarf generation. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: live-patching@vger.kernel.org Link: http://lkml.kernel.org/r/678bd94c0566c6129bcc376cddb259c4c5633004.1498659915.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
193 lines
4.6 KiB
C
193 lines
4.6 KiB
C
/*
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* Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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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 "special.h"
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#include "warn.h"
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#define EX_ENTRY_SIZE 12
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#define EX_ORIG_OFFSET 0
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#define EX_NEW_OFFSET 4
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#define JUMP_ENTRY_SIZE 24
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#define JUMP_ORIG_OFFSET 0
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#define JUMP_NEW_OFFSET 8
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#define ALT_ENTRY_SIZE 13
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#define ALT_ORIG_OFFSET 0
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#define ALT_NEW_OFFSET 4
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#define ALT_FEATURE_OFFSET 8
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#define ALT_ORIG_LEN_OFFSET 10
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#define ALT_NEW_LEN_OFFSET 11
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#define X86_FEATURE_POPCNT (4*32+23)
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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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};
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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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},
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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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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 rela *orig_rela, *new_rela;
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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 = *(unsigned short *)(sec->data->d_buf + offset +
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entry->feature);
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/*
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* It has been requested that we don't validate the !POPCNT
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* feature path which is a "very very small percentage of
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* machines".
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*/
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if (feature == X86_FEATURE_POPCNT)
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alt->skip_orig = true;
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}
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orig_rela = find_rela_by_dest(sec, offset + entry->orig);
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if (!orig_rela) {
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WARN_FUNC("can't find orig rela", sec, offset + entry->orig);
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return -1;
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}
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if (orig_rela->sym->type != STT_SECTION) {
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WARN_FUNC("don't know how to handle non-section rela symbol %s",
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sec, offset + entry->orig, orig_rela->sym->name);
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return -1;
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}
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alt->orig_sec = orig_rela->sym->sec;
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alt->orig_off = orig_rela->addend;
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if (!entry->group || alt->new_len) {
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new_rela = find_rela_by_dest(sec, offset + entry->new);
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if (!new_rela) {
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WARN_FUNC("can't find new rela",
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sec, offset + entry->new);
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return -1;
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}
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alt->new_sec = new_rela->sym->sec;
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alt->new_off = (unsigned int)new_rela->addend;
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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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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->len % 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->len / 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)
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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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