[linux.git] / lib / test_fpu.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Test cases for using floating point operations inside a kernel module.
 *
 * This tests kernel_fpu_begin() and kernel_fpu_end() functions, especially
 * when userland has modified the floating point control registers. The kernel
 * state might depend on the state set by the userland thread that was active
 * before a syscall.
 *
 * To facilitate the test, this module registers file
 * /sys/kernel/debug/selftest_helpers/test_fpu, which when read causes a
 * sequence of floating point operations. If the operations fail, either the
 * read returns error status or the kernel crashes.
 * If the operations succeed, the read returns "1\n".
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/debugfs.h>
#include <asm/fpu/api.h>

static int test_fpu(void)
{
	/*
	 * This sequence of operations tests that rounding mode is
	 * to nearest and that denormal numbers are supported.
	 * Volatile variables are used to avoid compiler optimizing
	 * the calculations away.
	 */
	volatile double a, b, c, d, e, f, g;

	a = 4.0;
	b = 1e-15;
	c = 1e-310;

	/* Sets precision flag */
	d = a + b;

	/* Result depends on rounding mode */
	e = a + b / 2;

	/* Denormal and very large values */
	f = b / c;

	/* Depends on denormal support */
	g = a + c * f;

	if (d > a && e > a && g > a)
		return 0;
	else
		return -EINVAL;
}

static int test_fpu_get(void *data, u64 *val)
{
	int status = -EINVAL;

	kernel_fpu_begin();
	status = test_fpu();
	kernel_fpu_end();

	*val = 1;
	return status;
}

DEFINE_DEBUGFS_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
static struct dentry *selftest_dir;

static int __init test_fpu_init(void)
{
	selftest_dir = debugfs_create_dir("selftest_helpers", NULL);
	if (!selftest_dir)
		return -ENOMEM;

	debugfs_create_file_unsafe("test_fpu", 0444, selftest_dir, NULL,
				   &test_fpu_fops);

	return 0;
}

static void __exit test_fpu_exit(void)
{
	debugfs_remove(selftest_dir);
}

module_init(test_fpu_init);
module_exit(test_fpu_exit);

MODULE_LICENSE("GPL");
Commit	Line	Data
4185b3b9 PA	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 <asm/fpu/api.h>
	21
	22	static int test_fpu(void)
	23	{
	24	/*
	25	* This sequence of operations tests that rounding mode is
	26	* to nearest and that denormal numbers are supported.
	27	* Volatile variables are used to avoid compiler optimizing
	28	* the calculations away.
	29	*/
	30	volatile double a, b, c, d, e, f, g;
	31
	32	a = 4.0;
	33	b = 1e-15;
	34	c = 1e-310;
	35
	36	/* Sets precision flag */
	37	d = a + b;
	38
	39	/* Result depends on rounding mode */
	40	e = a + b / 2;
	41
	42	/* Denormal and very large values */
	43	f = b / c;
	44
	45	/* Depends on denormal support */
	46	g = a + c * f;
	47
	48	if (d > a && e > a && g > a)
	49	return 0;
	50	else
	51	return -EINVAL;
	52	}
	53
	54	static int test_fpu_get(void data, u64 val)
	55	{
	56	int status = -EINVAL;
	57
	58	kernel_fpu_begin();
	59	status = test_fpu();
	60	kernel_fpu_end();
	61
	62	*val = 1;
	63	return status;
	64	}
65
443121b3	66	DEFINE_DEBUGFS_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
4185b3b9 PA	67	static struct dentry *selftest_dir;
	68
	69	static int __init test_fpu_init(void)
	70	{
	71	selftest_dir = debugfs_create_dir("selftest_helpers", NULL);
	72	if (!selftest_dir)
	73	return -ENOMEM;
	74
443121b3	75	debugfs_create_file_unsafe("test_fpu", 0444, selftest_dir, NULL,
443121b3	76	&test_fpu_fops);
4185b3b9 PA	77
	78	return 0;
	79	}
	80
	81	static void __exit test_fpu_exit(void)
	82	{
	83	debugfs_remove(selftest_dir);
	84	}
	85
	86	module_init(test_fpu_init);
	87	module_exit(test_fpu_exit);
	88
	89	MODULE_LICENSE("GPL");