LXR linux/lib/test

   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");
  90