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 */
frob_text(const struct module_layout * layout,int (* set_memory)(unsigned long start,int num_pages))35 static 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
frob_rodata(const struct module_layout * layout,int (* set_memory)(unsigned long start,int num_pages))42 static 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
frob_ro_after_init(const struct module_layout * layout,int (* set_memory)(unsigned long start,int num_pages))49 static 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
frob_writable_data(const struct module_layout * layout,int (* set_memory)(unsigned long start,int num_pages))56 static 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
layout_check_misalignment(const struct module_layout * layout)63 static 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
module_check_misalignment(const struct module * mod)72 bool 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
module_enable_x(const struct module * mod)82 void 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
module_enable_ro(const struct module * mod,bool after_init)92 void 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
module_enable_nx(const struct module * mod)113 void 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
module_enforce_rwx_sections(Elf_Ehdr * hdr,Elf_Shdr * sechdrs,char * secstrings,struct module * mod)125 int 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 }
144