cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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test_fpu.c (2052B)

      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
     22static 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
     54static 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
     66DEFINE_DEBUGFS_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
     67static struct dentry *selftest_dir;
     68
     69static int __init test_fpu_init(void)
     70{
     71	selftest_dir = debugfs_create_dir("selftest_helpers", NULL);
     72	if (!selftest_dir)
     73		return -ENOMEM;
     74
     75	debugfs_create_file_unsafe("test_fpu", 0444, selftest_dir, NULL,
     76				   &test_fpu_fops);
     77
     78	return 0;
     79}
     80
     81static void __exit test_fpu_exit(void)
     82{
     83	debugfs_remove(selftest_dir);
     84}
     85
     86module_init(test_fpu_init);
     87module_exit(test_fpu_exit);
     88
     89MODULE_LICENSE("GPL");