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 "internal.h"
 13
 14/*
 15 * LKM RO/NX protection: protect module's text/ro-data
 16 * from modification and any data from execution.
 17 *
 18 * General layout of module is:
 19 *          [text] [read-only-data] [ro-after-init] [writable data]
 20 * text_size -----^                ^               ^               ^
 21 * ro_size ------------------------|               |               |
 22 * ro_after_init_size -----------------------------|               |
 23 * size -----------------------------------------------------------|
 24 *
 25 * These values are always page-aligned (as is base) when
 26 * CONFIG_STRICT_MODULE_RWX is set.
 27 */
 28
 29/*
 30 * Since some arches are moving towards PAGE_KERNEL module allocations instead
 31 * of PAGE_KERNEL_EXEC, keep frob_text() and module_enable_x() independent of
 32 * CONFIG_STRICT_MODULE_RWX because they are needed regardless of whether we
 33 * are strict.
 34 */
 35static void frob_text(const struct module_layout *layout,
 36		      int (*set_memory)(unsigned long start, int num_pages))
 37{
 38	set_memory((unsigned long)layout->base,
 39		   PAGE_ALIGN(layout->text_size) >> PAGE_SHIFT);
 40}
 41
 42static void frob_rodata(const struct module_layout *layout,
 43		 int (*set_memory)(unsigned long start, int num_pages))
 44{
 45	set_memory((unsigned long)layout->base + layout->text_size,
 46		   (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
 47}
 48
 49static void frob_ro_after_init(const struct module_layout *layout,
 50			int (*set_memory)(unsigned long start, int num_pages))
 51{
 52	set_memory((unsigned long)layout->base + layout->ro_size,
 53		   (layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
 54}
 55
 56static void frob_writable_data(const struct module_layout *layout,
 57			int (*set_memory)(unsigned long start, int num_pages))
 58{
 59	set_memory((unsigned long)layout->base + layout->ro_after_init_size,
 60		   (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
 61}
 62
 63static bool layout_check_misalignment(const struct module_layout *layout)
 64{
 65	return WARN_ON(!PAGE_ALIGNED(layout->base)) ||
 66	       WARN_ON(!PAGE_ALIGNED(layout->text_size)) ||
 67	       WARN_ON(!PAGE_ALIGNED(layout->ro_size)) ||
 68	       WARN_ON(!PAGE_ALIGNED(layout->ro_after_init_size)) ||
 69	       WARN_ON(!PAGE_ALIGNED(layout->size));
 70}
 71
 72bool module_check_misalignment(const struct module *mod)
 73{
 74	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
 75		return false;
 76
 77	return layout_check_misalignment(&mod->core_layout) ||
 78	       layout_check_misalignment(&mod->data_layout) ||
 79	       layout_check_misalignment(&mod->init_layout);
 80}
 81
 82void module_enable_x(const struct module *mod)
 83{
 84	if (!PAGE_ALIGNED(mod->core_layout.base) ||
 85	    !PAGE_ALIGNED(mod->init_layout.base))
 86		return;
 87
 88	frob_text(&mod->core_layout, set_memory_x);
 89	frob_text(&mod->init_layout, set_memory_x);
 90}
 91
 92void module_enable_ro(const struct module *mod, bool after_init)
 93{
 94	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
 95		return;
 96#ifdef CONFIG_STRICT_MODULE_RWX
 97	if (!rodata_enabled)
 98		return;
 99#endif
100
101	set_vm_flush_reset_perms(mod->core_layout.base);
102	set_vm_flush_reset_perms(mod->init_layout.base);
103	frob_text(&mod->core_layout, set_memory_ro);
104
105	frob_rodata(&mod->data_layout, set_memory_ro);
106	frob_text(&mod->init_layout, set_memory_ro);
107	frob_rodata(&mod->init_layout, set_memory_ro);
108
109	if (after_init)
110		frob_ro_after_init(&mod->data_layout, set_memory_ro);
111}
112
113void module_enable_nx(const struct module *mod)
114{
115	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
116		return;
117
118	frob_rodata(&mod->data_layout, set_memory_nx);
119	frob_ro_after_init(&mod->data_layout, set_memory_nx);
120	frob_writable_data(&mod->data_layout, set_memory_nx);
121	frob_rodata(&mod->init_layout, set_memory_nx);
122	frob_writable_data(&mod->init_layout, set_memory_nx);
123}
124
125int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
126				char *secstrings, struct module *mod)
127{
128	const unsigned long shf_wx = SHF_WRITE | SHF_EXECINSTR;
129	int i;
130
131	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
132		return 0;
133
134	for (i = 0; i < hdr->e_shnum; i++) {
135		if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
136			pr_err("%s: section %s (index %d) has invalid WRITE|EXEC flags\n",
137			       mod->name, secstrings + sechdrs[i].sh_name, i);
138			return -ENOEXEC;
139		}
140	}
141
142	return 0;
143}