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
24static 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
36DEFINE_DEBUGFS_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
37static struct dentry *selftest_dir;
38
39static 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
54static void __exit test_fpu_exit(void)
55{
56	debugfs_remove(selftest_dir);
57}
58
59module_init(test_fpu_init);
60module_exit(test_fpu_exit);
61
62MODULE_DESCRIPTION("Test cases for floating point operations");
63MODULE_LICENSE("GPL");