strict_rwx.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * Module strict rwx
  4 *
  5 * Copyright (C) 2015 Rusty Russell
  6 */
  7
  8#include <linux/module.h>
  9#include <linux/mm.h>
 10#include <linux/vmalloc.h>
 11#include <linux/set_memory.h>
 12#include <linux/execmem.h>
 13#include "internal.h"
 14
 15static int module_set_memory(const struct module *mod, enum mod_mem_type type,
 16			     int (*set_memory)(unsigned long start, int num_pages))
 17{
 18	const struct module_memory *mod_mem = &mod->mem[type];
 19
 20	if (!mod_mem->base)
 21		return 0;
 22
 23	set_vm_flush_reset_perms(mod_mem->base);
 24	return set_memory((unsigned long)mod_mem->base, mod_mem->size >> PAGE_SHIFT);
 25}
 26
 27/*
 28 * Since some arches are moving towards PAGE_KERNEL module allocations instead
 29 * of PAGE_KERNEL_EXEC, keep module_enable_x() independent of
 30 * CONFIG_STRICT_MODULE_RWX because they are needed regardless of whether we
 31 * are strict.
 32 */
 33int module_enable_text_rox(const struct module *mod)
 34{
 35	for_class_mod_mem_type(type, text) {
 36		const struct module_memory *mem = &mod->mem[type];
 37		int ret;
 38
 39		if (mem->is_rox)
 40			ret = execmem_restore_rox(mem->base, mem->size);
 41		else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
 42			ret = module_set_memory(mod, type, set_memory_rox);
 43		else
 44			ret = module_set_memory(mod, type, set_memory_x);
 45		if (ret)
 46			return ret;
 47	}
 48	return 0;
 49}
 50
 51int module_enable_rodata_ro(const struct module *mod)
 52{
 53	int ret;
 54
 55	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX) || !rodata_enabled)
 56		return 0;
 57
 58	ret = module_set_memory(mod, MOD_RODATA, set_memory_ro);
 59	if (ret)
 60		return ret;
 61	ret = module_set_memory(mod, MOD_INIT_RODATA, set_memory_ro);
 62	if (ret)
 63		return ret;
 64
 65	return 0;
 66}
 67
 68int module_enable_rodata_ro_after_init(const struct module *mod)
 69{
 70	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX) || !rodata_enabled)
 71		return 0;
 72
 73	return module_set_memory(mod, MOD_RO_AFTER_INIT, set_memory_ro);
 74}
 75
 76int module_enable_data_nx(const struct module *mod)
 77{
 78	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
 79		return 0;
 80
 81	for_class_mod_mem_type(type, data) {
 82		int ret = module_set_memory(mod, type, set_memory_nx);
 83
 84		if (ret)
 85			return ret;
 86	}
 87	return 0;
 88}
 89
 90int module_enforce_rwx_sections(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
 91				const char *secstrings,
 92				const struct module *mod)
 93{
 94	const unsigned long shf_wx = SHF_WRITE | SHF_EXECINSTR;
 95	int i;
 96
 97	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
 98		return 0;
 99
100	for (i = 0; i < hdr->e_shnum; i++) {
101		if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
102			pr_err("%s: section %s (index %d) has invalid WRITE|EXEC flags\n",
103			       mod->name, secstrings + sechdrs[i].sh_name, i);
104			return -ENOEXEC;
105		}
106	}
107
108	return 0;
109}
110
111static const char *const ro_after_init[] = {
112	/*
113	 * Section .data..ro_after_init holds data explicitly annotated by
114	 * __ro_after_init.
115	 */
116	".data..ro_after_init",
117
118	/*
119	 * Section __jump_table holds data structures that are never modified,
120	 * with the exception of entries that refer to code in the __init
121	 * section, which are marked as such at module load time.
122	 */
123	"__jump_table",
124
125#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
126	/*
127	 * Section .static_call_sites holds data structures that need to be
128	 * sorted and processed at module load time but are never modified
129	 * afterwards.
130	 */
131	".static_call_sites",
132#endif
133};
134
135void module_mark_ro_after_init(const Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
136			       const char *secstrings)
137{
138	int i, j;
139
140	for (i = 1; i < hdr->e_shnum; i++) {
141		Elf_Shdr *shdr = &sechdrs[i];
142
143		for (j = 0; j < ARRAY_SIZE(ro_after_init); j++) {
144			if (strcmp(secstrings + shdr->sh_name,
145				   ro_after_init[j]) == 0) {
146				shdr->sh_flags |= SHF_RO_AFTER_INIT;
147				break;
148			}
149		}
150	}
151}