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
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
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 (!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
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
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