// 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 <linux/fpu.h> #include "test_fpu.h" 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) { if (!kernel_fpu_available()) return -EINVAL; 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");