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
19extern 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 */
45static 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 */
71void 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 */
80static 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
107static unsigned char test_data = 0xC3; /* 0xC3 is the opcode for "ret" */
108
109static 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#ifdef CONFIG_DEBUG_RODATA
146	/* Test 3: Check if the .rodata section is executable */
147	if (rodata_test_data != 0xC3) {
148		printk(KERN_ERR "test_nx: .rodata marker has invalid value\n");
149		ret = -ENODEV;
150	} else if (test_address(&rodata_test_data)) {
151		printk(KERN_ERR "test_nx: .rodata section is executable\n");
152		ret = -ENODEV;
153	}
154#endif
155
156#if 0
157	/* Test 4: Check if the .data section of a module is executable */
158	if (test_address(&test_data)) {
159		printk(KERN_ERR "test_nx: .data section is executable\n");
160		ret = -ENODEV;
161	}
162
163#endif
164	return ret;
165}
166
167static void test_exit(void)
168{
169}
170
171module_init(test_NX);
172module_exit(test_exit);
173MODULE_LICENSE("GPL");
174MODULE_DESCRIPTION("Testcase for the NX infrastructure");
175MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
176