From 4185b3b92792eaec5869266e594338343421ffb0 Mon Sep 17 00:00:00 2001 From: Petteri Aimonen Date: Thu, 18 Jun 2020 16:37:37 +0200 Subject: selftests/fpu: Add an FPU selftest Add a selftest for the usage of FPU code in kernel mode. Currently only implemented for x86. In the future, kernel FPU testing could be unified between the different architectures supporting it. [ bp: - Split out from a conglomerate patch, put comments over statements. - run the test only on debugfs write. - Add bare-minimum run_test_fpu.sh, run 1000 iterations on all CPUs by default. - Add conditionally -msse2 so that clang doesn't generate library calls. - Use cc-option to detect gcc 7.1 not supporting -mpreferred-stack-boundary=3 (amluto). - Document stuff so that we don't forget. - Fix: ld: lib/test_fpu.o: in function `test_fpu_get': >> test_fpu.c:(.text+0x16e): undefined reference to `__sanitizer_cov_trace_cmpd' >> ld: test_fpu.c:(.text+0x1a7): undefined reference to `__sanitizer_cov_trace_cmpd' ld: test_fpu.c:(.text+0x1e0): undefined reference to `__sanitizer_cov_trace_cmpd' ] Reported-by: kernel test robot Signed-off-by: Petteri Aimonen Signed-off-by: Borislav Petkov Reviewed-by: Nick Desaulniers Link: https://lkml.kernel.org/r/20200624114646.28953-3-bp@alien8.de --- lib/test_fpu.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) create mode 100644 lib/test_fpu.c (limited to 'lib/test_fpu.c') diff --git a/lib/test_fpu.c b/lib/test_fpu.c new file mode 100644 index 000000000000..c33764aa3eb8 --- /dev/null +++ b/lib/test_fpu.c @@ -0,0 +1,89 @@ +// 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 +#include +#include +#include + +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_SIMPLE_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("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"); -- cgit v1.2.3-58-ga151