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x86: Set FSGSBASE to active if enabled by kernel

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Linux kernel uses AT_HWCAP2 to indicate if FSGSBASE instructions are
enabled.  If the HWCAP2_FSGSBASE bit in AT_HWCAP2 is set, FSGSBASE
instructions can be used in user space.  Define dl_check_hwcap2 to set
the FSGSBASE feature to active on Linux when the HWCAP2_FSGSBASE bit is
set.

Add a test to verify that FSGSBASE is active on current kernels.
NB: This test will fail if the kernel doesn't set the HWCAP2_FSGSBASE
bit in AT_HWCAP2 while fsgsbase shows up in /proc/cpuinfo.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
This commit is contained in:
H.J. Lu 2023-03-15 17:42:54 -07:00
parent 5d1ccdda7b
commit 743113d42e
4 changed files with 58 additions and 0 deletions
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27
sysdeps/unix/sysv/linux/x86/dl-hwcap2.h Normal file
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@ -0,0 +1,27 @@
/* Handle AT_HWCAP2. Linux/x86 version.
Copyright (C) 2023 Free Software Foundation, Inc.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/* The following must match the kernel's <asm/hwcap2.h>. */
#define HWCAP2_RING3MWAIT (1 << 0)
#define HWCAP2_FSGSBASE (1 << 1)
static inline void
dl_check_hwcap2 (struct cpu_features *cpu_features)
{
if ((GLRO(dl_hwcap2) & HWCAP2_FSGSBASE) != 0)
CPU_FEATURE_SET_ACTIVE (cpu_features, FSGSBASE);
}

3
sysdeps/x86/cpu-features.c
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@ -22,6 +22,7 @@
#include <cacheinfo.h> #include <cacheinfo.h>
#include <dl-cacheinfo.h> #include <dl-cacheinfo.h>
#include <dl-minsigstacksize.h> #include <dl-minsigstacksize.h>
#include <dl-hwcap2.h>
extern void TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *) extern void TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *)
attribute_hidden; attribute_hidden;
@ -299,6 +300,8 @@ update_active (struct cpu_features *cpu_features)
CPU_FEATURE_SET_ACTIVE (cpu_features, WIDE_KL); CPU_FEATURE_SET_ACTIVE (cpu_features, WIDE_KL);
} }
dl_check_hwcap2 (cpu_features);
cpu_features->isa_1 = get_isa_level (cpu_features); cpu_features->isa_1 = get_isa_level (cpu_features);
} }

21
sysdeps/x86/dl-hwcap2.h Normal file
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@ -0,0 +1,21 @@
/* Handle AT_HWCAP2. Generic x86 version.
Copyright (C) 2023 Free Software Foundation, Inc.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
static inline void
dl_check_hwcap2 (struct cpu_features *cpu_features)
{
}

7
sysdeps/x86/tst-cpu-features-cpuinfo.c
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@ -96,6 +96,11 @@ check_proc (const char *proc_name, const char *search_name, int flag,
CPU_FEATURE_USABLE (name), \ CPU_FEATURE_USABLE (name), \
"HAS_CPU_FEATURE (" #name ")") "HAS_CPU_FEATURE (" #name ")")
#define CHECK_PROC_ACTIVE(str, name) \
check_proc (#str, " "#str" ", CPU_FEATURE_USABLE (name), \
CPU_FEATURE_USABLE (name), \
"CPU_FEATURE_USABLE (" #name ")")
static int static int
do_test (int argc, char **argv) do_test (int argc, char **argv)
{ {
@ -298,6 +303,8 @@ do_test (int argc, char **argv)
fails += CHECK_PROC (xsaves, XSAVES); fails += CHECK_PROC (xsaves, XSAVES);
fails += CHECK_PROC (xtpr, XTPRUPDCTRL); fails += CHECK_PROC (xtpr, XTPRUPDCTRL);
fails += CHECK_PROC_ACTIVE (fsgsbase, FSGSBASE);
printf ("%d differences between /proc/cpuinfo and glibc code.\n", fails); printf ("%d differences between /proc/cpuinfo and glibc code.\n", fails);
return (fails != 0); return (fails != 0);