Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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 <lkp@intel.com>
Signed-off-by: Petteri Aimonen <jpa@git.mail.kapsi.fi>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/20200624114646.28953-3-bp@alien8.de
authored by
Petteri Aimonen
and committed by
Borislav Petkov
4185b3b9
7ad81676
+243
+11
lib/Kconfig.debug
+11
lib/Kconfig.debug
···
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If unsure, say N.
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config TEST_FPU
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tristate "Test floating point operations in kernel space"
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depends on X86 && !KCOV_INSTRUMENT_ALL
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help
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Enable this option to add /sys/kernel/debug/selftest_helpers/test_fpu
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which will trigger a sequence of floating point operations. This is used
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for self-testing floating point control register setting in
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kernel_fpu_begin().
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If unsure, say N.
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endif # RUNTIME_TESTING_MENU
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config MEMTEST
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lib/Makefile
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lib/Makefile
···
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obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o
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obj-$(CONFIG_TEST_HMM) += test_hmm.o
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#
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# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
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# off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS
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# get appended last to CFLAGS and thus override those previous compiler options.
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#
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FPU_CFLAGS := -mhard-float -msse -msse2
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ifdef CONFIG_CC_IS_GCC
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# Stack alignment mismatch, proceed with caution.
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# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3
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# (8B stack alignment).
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# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
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#
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# The "-msse" in the first argument is there so that the
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# -mpreferred-stack-boundary=3 build error:
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#
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# -mpreferred-stack-boundary=3 is not between 4 and 12
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#
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# can be triggered. Otherwise gcc doesn't complain.
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FPU_CFLAGS += $(call cc-option,-msse -mpreferred-stack-boundary=3,-mpreferred-stack-boundary=4)
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endif
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+
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obj-$(CONFIG_TEST_FPU) += test_fpu.o
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CFLAGS_test_fpu.o += $(FPU_CFLAGS)
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obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
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obj-$(CONFIG_KUNIT) += kunit/
+89
lib/test_fpu.c
+89
lib/test_fpu.c
···
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// SPDX-License-Identifier: GPL-2.0+
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/*
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* Test cases for using floating point operations inside a kernel module.
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*
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* This tests kernel_fpu_begin() and kernel_fpu_end() functions, especially
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* when userland has modified the floating point control registers. The kernel
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* state might depend on the state set by the userland thread that was active
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* before a syscall.
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*
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* To facilitate the test, this module registers file
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* /sys/kernel/debug/selftest_helpers/test_fpu, which when read causes a
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* sequence of floating point operations. If the operations fail, either the
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* read returns error status or the kernel crashes.
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* If the operations succeed, the read returns "1\n".
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*/
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/debugfs.h>
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#include <asm/fpu/api.h>
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static int test_fpu(void)
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{
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/*
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* This sequence of operations tests that rounding mode is
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* to nearest and that denormal numbers are supported.
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* Volatile variables are used to avoid compiler optimizing
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* the calculations away.
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*/
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volatile double a, b, c, d, e, f, g;
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a = 4.0;
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b = 1e-15;
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c = 1e-310;
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/* Sets precision flag */
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d = a + b;
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/* Result depends on rounding mode */
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e = a + b / 2;
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/* Denormal and very large values */
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f = b / c;
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/* Depends on denormal support */
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g = a + c * f;
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if (d > a && e > a && g > a)
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return 0;
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else
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return -EINVAL;
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}
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static int test_fpu_get(void *data, u64 *val)
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{
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int status = -EINVAL;
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kernel_fpu_begin();
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status = test_fpu();
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kernel_fpu_end();
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*val = 1;
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return status;
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}
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DEFINE_SIMPLE_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
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static struct dentry *selftest_dir;
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static int __init test_fpu_init(void)
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{
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selftest_dir = debugfs_create_dir("selftest_helpers", NULL);
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if (!selftest_dir)
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return -ENOMEM;
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debugfs_create_file("test_fpu", 0444, selftest_dir, NULL,
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&test_fpu_fops);
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return 0;
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}
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static void __exit test_fpu_exit(void)
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{
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debugfs_remove(selftest_dir);
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}
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module_init(test_fpu_init);
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module_exit(test_fpu_exit);
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MODULE_LICENSE("GPL");
+1
tools/testing/selftests/Makefile
+1
tools/testing/selftests/Makefile
+9
tools/testing/selftests/fpu/Makefile
+9
tools/testing/selftests/fpu/Makefile
+46
tools/testing/selftests/fpu/run_test_fpu.sh
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tools/testing/selftests/fpu/run_test_fpu.sh
···
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#!/bin/bash
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# SPDX-License-Identifier: GPL-2.0
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#
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# Load kernel module for FPU tests
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uid=$(id -u)
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if [ $uid -ne 0 ]; then
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echo "$0: Must be run as root"
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exit 1
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fi
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if ! which modprobe > /dev/null 2>&1; then
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echo "$0: You need modprobe installed"
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exit 4
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fi
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if ! modinfo test_fpu > /dev/null 2>&1; then
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echo "$0: You must have the following enabled in your kernel:"
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echo "CONFIG_TEST_FPU=m"
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exit 4
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fi
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NR_CPUS=$(getconf _NPROCESSORS_ONLN)
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if [ ! $NR_CPUS ]; then
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NR_CPUS=1
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fi
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modprobe test_fpu
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if [ ! -e /sys/kernel/debug/selftest_helpers/test_fpu ]; then
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mount -t debugfs none /sys/kernel/debug
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if [ ! -e /sys/kernel/debug/selftest_helpers/test_fpu ]; then
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echo "$0: Error mounting debugfs"
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exit 4
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fi
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fi
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echo "Running 1000 iterations on all CPUs... "
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for i in $(seq 1 1000); do
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for c in $(seq 1 $NR_CPUS); do
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./test_fpu &
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done
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done
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rmmod test_fpu
+61
tools/testing/selftests/fpu/test_fpu.c
+61
tools/testing/selftests/fpu/test_fpu.c
···
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// SPDX-License-Identifier: GPL-2.0+
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/* This testcase operates with the test_fpu kernel driver.
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* It modifies the FPU control register in user mode and calls the kernel
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* module to perform floating point operations in the kernel. The control
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* register value should be independent between kernel and user mode.
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*/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <errno.h>
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#include <string.h>
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#include <fenv.h>
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#include <unistd.h>
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#include <fcntl.h>
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const char *test_fpu_path = "/sys/kernel/debug/selftest_helpers/test_fpu";
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int main(void)
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{
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char dummy[1];
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int fd = open(test_fpu_path, O_RDONLY);
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if (fd < 0) {
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printf("[SKIP]\tcan't access %s: %s\n",
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test_fpu_path, strerror(errno));
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return 0;
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}
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if (read(fd, dummy, 1) < 0) {
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printf("[FAIL]\taccess with default rounding mode failed\n");
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return 1;
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}
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fesetround(FE_DOWNWARD);
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if (read(fd, dummy, 1) < 0) {
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printf("[FAIL]\taccess with downward rounding mode failed\n");
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return 2;
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}
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if (fegetround() != FE_DOWNWARD) {
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printf("[FAIL]\tusermode rounding mode clobbered\n");
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return 3;
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}
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/* Note: the tests up to this point are quite safe and will only return
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* an error. But the exception mask setting can cause misbehaving kernel
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* to crash.
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*/
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feclearexcept(FE_ALL_EXCEPT);
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feenableexcept(FE_ALL_EXCEPT);
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if (read(fd, dummy, 1) < 0) {
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printf("[FAIL]\taccess with fpu exceptions unmasked failed\n");
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return 4;
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}
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if (fegetexcept() != FE_ALL_EXCEPT) {
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printf("[FAIL]\tusermode fpu exception mask clobbered\n");
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return 5;
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}
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printf("[OK]\ttest_fpu\n");
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return 0;
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}