lib/test_fpu_glue.c

   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 (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
  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");