// 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 "builtin.h"#include "special.h"#include "warn.h" #define EX_ENTRY_SIZE		12#define EX_ORIG_OFFSET		0#define EX_NEW_OFFSET		4 #define JUMP_ENTRY_SIZE		16#define JUMP_ORIG_OFFSET	0#define JUMP_NEW_OFFSET		4 #define ALT_ENTRY_SIZE		13#define ALT_ORIG_OFFSET		0#define ALT_NEW_OFFSET		4#define ALT_FEATURE_OFFSET	8#define ALT_ORIG_LEN_OFFSET	10#define ALT_NEW_LEN_OFFSET	11 #define X86_FEATURE_POPCNT (4*32+23)#define X86_FEATURE_SMAP   (9*32+20) 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 */}; 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,	},	{		.sec = "__ex_table",		.size = EX_ENTRY_SIZE,		.orig = EX_ORIG_OFFSET,		.new = EX_NEW_OFFSET,	},	{},}; 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 = *(unsigned short *)(sec->data->d_buf + offset +					      entry->feature); 		/*		 * It has been requested that we don't validate the !POPCNT		 * feature path which is a "very very small percentage of		 * machines".		 */		if (feature == X86_FEATURE_POPCNT)			alt->skip_orig = true; 		/*		 * If UACCESS validation is enabled; force that alternative;		 * otherwise force it the other way.		 *		 * What we want to avoid is having both the original and the		 * alternative code flow at the same time, in that case we can		 * find paths that see the STAC but take the NOP instead of		 * CLAC and the other way around.		 */		if (feature == X86_FEATURE_SMAP) {			if (uaccess)				alt->skip_orig = true;			else				alt->skip_alt = true;		}	} 	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;		} 		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;	} 	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)				return ret; 			list_add_tail(&alt->list, alts);		}	} 	return 0;}