4185b3b927
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
90 lines
2.0 KiB
C
90 lines
2.0 KiB
C
// 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");
|