1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * Test cases for using floating point operations inside a kernel module.
4  *
5  * This tests kernel_fpu_begin() and kernel_fpu_end() functions, especially
6  * when userland has modified the floating point control registers. The kernel
7  * state might depend on the state set by the userland thread that was active
8  * before a syscall.
9  *
10  * To facilitate the test, this module registers file
11  * /sys/kernel/debug/selftest_helpers/test_fpu, which when read causes a
12  * sequence of floating point operations. If the operations fail, either the
13  * read returns error status or the kernel crashes.
14  * If the operations succeed, the read returns "1\n".
15  */
16 
17 #include <linux/module.h>
18 #include <linux/kernel.h>
19 #include <linux/debugfs.h>
20 #include <linux/fpu.h>
21 
22 #include "test_fpu.h"
23 
test_fpu_get(void * data,u64 * val)24 static int test_fpu_get(void *data, u64 *val)
25 {
26 	int status = -EINVAL;
27 
28 	kernel_fpu_begin();
29 	status = test_fpu();
30 	kernel_fpu_end();
31 
32 	*val = 1;
33 	return status;
34 }
35 
36 DEFINE_DEBUGFS_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
37 static struct dentry *selftest_dir;
38 
test_fpu_init(void)39 static int __init test_fpu_init(void)
40 {
41 	if (!kernel_fpu_available())
42 		return -EINVAL;
43 
44 	selftest_dir = debugfs_create_dir("selftest_helpers", NULL);
45 	if (IS_ERR(selftest_dir))
46 		return -ENOMEM;
47 
48 	debugfs_create_file_unsafe("test_fpu", 0444, selftest_dir, NULL,
49 				   &test_fpu_fops);
50 
51 	return 0;
52 }
53 
test_fpu_exit(void)54 static void __exit test_fpu_exit(void)
55 {
56 	debugfs_remove(selftest_dir);
57 }
58 
59 module_init(test_fpu_init);
60 module_exit(test_fpu_exit);
61 
62 MODULE_DESCRIPTION("Test cases for floating point operations");
63 MODULE_LICENSE("GPL");
64