Commit 4185b3b9 authored by Petteri Aimonen's avatar Petteri Aimonen Committed by Borislav Petkov

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: default avatarkernel test robot <lkp@intel.com>
Signed-off-by: default avatarPetteri Aimonen <jpa@git.mail.kapsi.fi>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/20200624114646.28953-3-bp@alien8.de
parent 7ad81676
......@@ -2307,6 +2307,17 @@ config TEST_HMM
If unsure, say N.
config TEST_FPU
tristate "Test floating point operations in kernel space"
depends on X86 && !KCOV_INSTRUMENT_ALL
help
Enable this option to add /sys/kernel/debug/selftest_helpers/test_fpu
which will trigger a sequence of floating point operations. This is used
for self-testing floating point control register setting in
kernel_fpu_begin().
If unsure, say N.
endif # RUNTIME_TESTING_MENU
config MEMTEST
......
......@@ -99,6 +99,30 @@ obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o
obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o
obj-$(CONFIG_TEST_HMM) += test_hmm.o
#
# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
# off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS
# get appended last to CFLAGS and thus override those previous compiler options.
#
FPU_CFLAGS := -mhard-float -msse -msse2
ifdef CONFIG_CC_IS_GCC
# Stack alignment mismatch, proceed with caution.
# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3
# (8B stack alignment).
# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
#
# The "-msse" in the first argument is there so that the
# -mpreferred-stack-boundary=3 build error:
#
# -mpreferred-stack-boundary=3 is not between 4 and 12
#
# can be triggered. Otherwise gcc doesn't complain.
FPU_CFLAGS += $(call cc-option,-msse -mpreferred-stack-boundary=3,-mpreferred-stack-boundary=4)
endif
obj-$(CONFIG_TEST_FPU) += test_fpu.o
CFLAGS_test_fpu.o += $(FPU_CFLAGS)
obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
obj-$(CONFIG_KUNIT) += kunit/
......
// 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 <asm/fpu/api.h>
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");
......@@ -15,6 +15,7 @@ TARGETS += filesystems
TARGETS += filesystems/binderfs
TARGETS += filesystems/epoll
TARGETS += firmware
TARGETS += fpu
TARGETS += ftrace
TARGETS += futex
TARGETS += gpio
......
# SPDX-License-Identifier: GPL-2.0+
test_fpu
# SPDX-License-Identifier: GPL-2.0+
LDLIBS := -lm
TEST_GEN_PROGS := test_fpu
TEST_PROGS := run_test_fpu.sh
include ../lib.mk
#!/bin/bash
# SPDX-License-Identifier: GPL-2.0
#
# Load kernel module for FPU tests
uid=$(id -u)
if [ $uid -ne 0 ]; then
echo "$0: Must be run as root"
exit 1
fi
if ! which modprobe > /dev/null 2>&1; then
echo "$0: You need modprobe installed"
exit 4
fi
if ! modinfo test_fpu > /dev/null 2>&1; then
echo "$0: You must have the following enabled in your kernel:"
echo "CONFIG_TEST_FPU=m"
exit 4
fi
NR_CPUS=$(getconf _NPROCESSORS_ONLN)
if [ ! $NR_CPUS ]; then
NR_CPUS=1
fi
modprobe test_fpu
if [ ! -e /sys/kernel/debug/selftest_helpers/test_fpu ]; then
mount -t debugfs none /sys/kernel/debug
if [ ! -e /sys/kernel/debug/selftest_helpers/test_fpu ]; then
echo "$0: Error mounting debugfs"
exit 4
fi
fi
echo "Running 1000 iterations on all CPUs... "
for i in $(seq 1 1000); do
for c in $(seq 1 $NR_CPUS); do
./test_fpu &
done
done
rmmod test_fpu
// SPDX-License-Identifier: GPL-2.0+
/* This testcase operates with the test_fpu kernel driver.
* It modifies the FPU control register in user mode and calls the kernel
* module to perform floating point operations in the kernel. The control
* register value should be independent between kernel and user mode.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <fenv.h>
#include <unistd.h>
#include <fcntl.h>
const char *test_fpu_path = "/sys/kernel/debug/selftest_helpers/test_fpu";
int main(void)
{
char dummy[1];
int fd = open(test_fpu_path, O_RDONLY);
if (fd < 0) {
printf("[SKIP]\tcan't access %s: %s\n",
test_fpu_path, strerror(errno));
return 0;
}
if (read(fd, dummy, 1) < 0) {
printf("[FAIL]\taccess with default rounding mode failed\n");
return 1;
}
fesetround(FE_DOWNWARD);
if (read(fd, dummy, 1) < 0) {
printf("[FAIL]\taccess with downward rounding mode failed\n");
return 2;
}
if (fegetround() != FE_DOWNWARD) {
printf("[FAIL]\tusermode rounding mode clobbered\n");
return 3;
}
/* Note: the tests up to this point are quite safe and will only return
* an error. But the exception mask setting can cause misbehaving kernel
* to crash.
*/
feclearexcept(FE_ALL_EXCEPT);
feenableexcept(FE_ALL_EXCEPT);
if (read(fd, dummy, 1) < 0) {
printf("[FAIL]\taccess with fpu exceptions unmasked failed\n");
return 4;
}
if (fegetexcept() != FE_ALL_EXCEPT) {
printf("[FAIL]\tusermode fpu exception mask clobbered\n");
return 5;
}
printf("[OK]\ttest_fpu\n");
return 0;
}
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