1 /*
2 * test_nx.c: functional test for NX functionality
3 *
4 * (C) Copyright 2008 Intel Corporation
5 * Author: Arjan van de Ven <arjan@linux.intel.com>
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; version 2
10 * of the License.
11 */
12 #include <linux/module.h>
13 #include <linux/sort.h>
14 #include <linux/slab.h>
15
16 #include <asm/uaccess.h>
17 #include <asm/asm.h>
18
19 extern int rodata_test_data;
20
21 /*
22 * This file checks 4 things:
23 * 1) Check if the stack is not executable
24 * 2) Check if kmalloc memory is not executable
25 * 3) Check if the .rodata section is not executable
26 * 4) Check if the .data section of a module is not executable
27 *
28 * To do this, the test code tries to execute memory in stack/kmalloc/etc,
29 * and then checks if the expected trap happens.
30 *
31 * Sadly, this implies having a dynamic exception handling table entry.
32 * ... which can be done (and will make Rusty cry)... but it can only
33 * be done in a stand-alone module with only 1 entry total.
34 * (otherwise we'd have to sort and that's just too messy)
35 */
36
37
38
39 /*
40 * We want to set up an exception handling point on our stack,
41 * which means a variable value. This function is rather dirty
42 * and walks the exception table of the module, looking for a magic
43 * marker and replaces it with a specific function.
44 */
fudze_exception_table(void * marker,void * new)45 static void fudze_exception_table(void *marker, void *new)
46 {
47 struct module *mod = THIS_MODULE;
48 struct exception_table_entry *extable;
49
50 /*
51 * Note: This module has only 1 exception table entry,
52 * so searching and sorting is not needed. If that changes,
53 * this would be the place to search and re-sort the exception
54 * table.
55 */
56 if (mod->num_exentries > 1) {
57 printk(KERN_ERR "test_nx: too many exception table entries!\n");
58 printk(KERN_ERR "test_nx: test results are not reliable.\n");
59 return;
60 }
61 extable = (struct exception_table_entry *)mod->extable;
62 extable[0].insn = (unsigned long)new;
63 }
64
65
66 /*
67 * exception tables get their symbols translated so we need
68 * to use a fake function to put in there, which we can then
69 * replace at runtime.
70 */
71 void foo_label(void);
72
73 /*
74 * returns 0 for not-executable, negative for executable
75 *
76 * Note: we cannot allow this function to be inlined, because
77 * that would give us more than 1 exception table entry.
78 * This in turn would break the assumptions above.
79 */
test_address(void * address)80 static noinline int test_address(void *address)
81 {
82 unsigned long result;
83
84 /* Set up an exception table entry for our address */
85 fudze_exception_table(&foo_label, address);
86 result = 1;
87 asm volatile(
88 "foo_label:\n"
89 "0: call *%[fake_code]\n"
90 "1:\n"
91 ".section .fixup,\"ax\"\n"
92 "2: mov %[zero], %[rslt]\n"
93 " ret\n"
94 ".previous\n"
95 _ASM_EXTABLE(0b,2b)
96 : [rslt] "=r" (result)
97 : [fake_code] "r" (address), [zero] "r" (0UL), "0" (result)
98 );
99 /* change the exception table back for the next round */
100 fudze_exception_table(address, &foo_label);
101
102 if (result)
103 return -ENODEV;
104 return 0;
105 }
106
107 static unsigned char test_data = 0xC3; /* 0xC3 is the opcode for "ret" */
108
test_NX(void)109 static int test_NX(void)
110 {
111 int ret = 0;
112 /* 0xC3 is the opcode for "ret" */
113 char stackcode[] = {0xC3, 0x90, 0 };
114 char *heap;
115
116 test_data = 0xC3;
117
118 printk(KERN_INFO "Testing NX protection\n");
119
120 /* Test 1: check if the stack is not executable */
121 if (test_address(&stackcode)) {
122 printk(KERN_ERR "test_nx: stack was executable\n");
123 ret = -ENODEV;
124 }
125
126
127 /* Test 2: Check if the heap is executable */
128 heap = kmalloc(64, GFP_KERNEL);
129 if (!heap)
130 return -ENOMEM;
131 heap[0] = 0xC3; /* opcode for "ret" */
132
133 if (test_address(heap)) {
134 printk(KERN_ERR "test_nx: heap was executable\n");
135 ret = -ENODEV;
136 }
137 kfree(heap);
138
139 /*
140 * The following 2 tests currently fail, this needs to get fixed
141 * Until then, don't run them to avoid too many people getting scared
142 * by the error message
143 */
144
145 /* Test 3: Check if the .rodata section is executable */
146 if (rodata_test_data != 0xC3) {
147 printk(KERN_ERR "test_nx: .rodata marker has invalid value\n");
148 ret = -ENODEV;
149 } else if (test_address(&rodata_test_data)) {
150 printk(KERN_ERR "test_nx: .rodata section is executable\n");
151 ret = -ENODEV;
152 }
153
154 #if 0
155 /* Test 4: Check if the .data section of a module is executable */
156 if (test_address(&test_data)) {
157 printk(KERN_ERR "test_nx: .data section is executable\n");
158 ret = -ENODEV;
159 }
160
161 #endif
162 return ret;
163 }
164
test_exit(void)165 static void test_exit(void)
166 {
167 }
168
169 module_init(test_NX);
170 module_exit(test_exit);
171 MODULE_LICENSE("GPL");
172 MODULE_DESCRIPTION("Testcase for the NX infrastructure");
173 MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
174