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glibc/sysdeps/x86/dl-cet.c
H.J. Lu 107e6a3c22 x86: Support usable check for all CPU features 
Support usable check for all CPU features with the following changes:

1. Change struct cpu_features to

struct cpuid_features
{
  struct cpuid_registers cpuid;
  struct cpuid_registers usable;
};

struct cpu_features
{
  struct cpu_features_basic basic;
  struct cpuid_features features[COMMON_CPUID_INDEX_MAX];
  unsigned int preferred[PREFERRED_FEATURE_INDEX_MAX];
...
};

so that there is a usable bit for each cpuid bit.
2. After the cpuid bits have been initialized, copy the known bits to the
usable bits.  EAX/EBX from INDEX_1 and EAX from INDEX_7 aren't used for
CPU feature detection.
3. Clear the usable bits which require OS support.
4. If the feature is supported by OS, copy its cpuid bit to its usable
bit.
5. Replace HAS_CPU_FEATURE and CPU_FEATURES_CPU_P with CPU_FEATURE_USABLE
and CPU_FEATURE_USABLE_P to check if a feature is usable.
6. Add DEPR_FPU_CS_DS for INDEX_7_EBX_13.
7. Unset MPX feature since it has been deprecated.

The results are

1. If the feature is known and doesn't requre OS support, its usable bit
is copied from the cpuid bit.
2. Otherwise, its usable bit is copied from the cpuid bit only if the
feature is known to supported by OS.
3. CPU_FEATURE_USABLE/CPU_FEATURE_USABLE_P are used to check if the
feature can be used.
4. HAS_CPU_FEATURE/CPU_FEATURE_CPU_P are used to check if CPU supports
the feature.
2020-07-13 06:05:16 -07:00

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/* x86 CET initializers function.
Copyright (C) 2018-2020 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/>. */
#include <unistd.h>
#include <errno.h>
#include <libintl.h>
#include <ldsodefs.h>
#include <dl-cet.h>
/* GNU_PROPERTY_X86_FEATURE_1_IBT and GNU_PROPERTY_X86_FEATURE_1_SHSTK
are defined in <elf.h>, which are only available for C sources.
X86_FEATURE_1_IBT and X86_FEATURE_1_SHSTK are defined in <sysdep.h>
which are available for both C and asm sources. They must match. */
#if GNU_PROPERTY_X86_FEATURE_1_IBT != X86_FEATURE_1_IBT
# error GNU_PROPERTY_X86_FEATURE_1_IBT != X86_FEATURE_1_IBT
#endif
#if GNU_PROPERTY_X86_FEATURE_1_SHSTK != X86_FEATURE_1_SHSTK
# error GNU_PROPERTY_X86_FEATURE_1_SHSTK != X86_FEATURE_1_SHSTK
#endif
/* Check if object M is compatible with CET. */
static void
dl_cet_check (struct link_map *m, const char *program)
{
/* Check how IBT should be enabled. */
enum dl_x86_cet_control enable_ibt_type
= GL(dl_x86_feature_control).ibt;
/* Check how SHSTK should be enabled. */
enum dl_x86_cet_control enable_shstk_type
= GL(dl_x86_feature_control).shstk;
/* No legacy object check if both IBT and SHSTK are always on. */
if (enable_ibt_type == cet_always_on
&& enable_shstk_type == cet_always_on)
return;
/* Check if IBT is enabled by kernel. */
bool ibt_enabled
= (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
/* Check if SHSTK is enabled by kernel. */
bool shstk_enabled
= (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
if (ibt_enabled || shstk_enabled)
{
struct link_map *l = NULL;
unsigned int ibt_legacy = 0, shstk_legacy = 0;
bool found_ibt_legacy = false, found_shstk_legacy = false;
/* Check if IBT and SHSTK are enabled in object. */
bool enable_ibt = (ibt_enabled
&& enable_ibt_type != cet_always_off);
bool enable_shstk = (shstk_enabled
&& enable_shstk_type != cet_always_off);
if (program)
{
/* Enable IBT and SHSTK only if they are enabled in executable.
NB: IBT and SHSTK may be disabled by environment variable:
GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK
*/
enable_ibt &= (CPU_FEATURE_USABLE (IBT)
&& (enable_ibt_type == cet_always_on
|| (m->l_cet & lc_ibt) != 0));
enable_shstk &= (CPU_FEATURE_USABLE (SHSTK)
&& (enable_shstk_type == cet_always_on
|| (m->l_cet & lc_shstk) != 0));
}
/* ld.so is CET-enabled by kernel. But shared objects may not
support IBT nor SHSTK. */
if (enable_ibt || enable_shstk)
{
unsigned int i;
i = m->l_searchlist.r_nlist;
while (i-- > 0)
{
/* Check each shared object to see if IBT and SHSTK are
enabled. */
l = m->l_initfini[i];
if (l->l_init_called)
continue;
#ifdef SHARED
/* Skip CET check for ld.so since ld.so is CET-enabled.
CET will be disabled later if CET isn't enabled in
executable. */
if (l == &GL(dl_rtld_map)
|| l->l_real == &GL(dl_rtld_map)
|| (program && l == m))
continue;
#endif
/* IBT is enabled only if it is enabled in executable as
well as all shared objects. */
enable_ibt &= (enable_ibt_type == cet_always_on
|| (l->l_cet & lc_ibt) != 0);
if (!found_ibt_legacy && enable_ibt != ibt_enabled)
{
found_ibt_legacy = true;
ibt_legacy = i;
}
/* SHSTK is enabled only if it is enabled in executable as
well as all shared objects. */
enable_shstk &= (enable_shstk_type == cet_always_on
|| (l->l_cet & lc_shstk) != 0);
if (enable_shstk != shstk_enabled)
{
found_shstk_legacy = true;
shstk_legacy = i;
}
}
}
bool cet_feature_changed = false;
if (enable_ibt != ibt_enabled || enable_shstk != shstk_enabled)
{
if (!program)
{
if (enable_ibt_type != cet_permissive)
{
/* When IBT is enabled, we cannot dlopen a shared
object without IBT. */
if (found_ibt_legacy)
_dl_signal_error (0,
m->l_initfini[ibt_legacy]->l_name,
"dlopen",
N_("rebuild shared object with IBT support enabled"));
}
if (enable_shstk_type != cet_permissive)
{
/* When SHSTK is enabled, we cannot dlopen a shared
object without SHSTK. */
if (found_shstk_legacy)
_dl_signal_error (0,
m->l_initfini[shstk_legacy]->l_name,
"dlopen",
N_("rebuild shared object with SHSTK support enabled"));
}
if (enable_ibt_type != cet_permissive
&& enable_shstk_type != cet_permissive)
return;
}
/* Disable IBT and/or SHSTK if they are enabled by kernel, but
disabled in executable or shared objects. */
unsigned int cet_feature = 0;
if (!enable_ibt)
cet_feature |= GNU_PROPERTY_X86_FEATURE_1_IBT;
if (!enable_shstk)
cet_feature |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
int res = dl_cet_disable_cet (cet_feature);
if (res != 0)
{
if (program)
_dl_fatal_printf ("%s: can't disable CET\n", program);
else
{
if (found_ibt_legacy)
l = m->l_initfini[ibt_legacy];
else
l = m->l_initfini[shstk_legacy];
_dl_signal_error (-res, l->l_name, "dlopen",
N_("can't disable CET"));
}
}
/* Clear the disabled bits in dl_x86_feature_1. */
GL(dl_x86_feature_1) &= ~cet_feature;
cet_feature_changed = true;
}
#ifdef SHARED
if (program && (ibt_enabled || shstk_enabled))
{
if ((!ibt_enabled
|| enable_ibt_type != cet_permissive)
&& (!shstk_enabled
|| enable_shstk_type != cet_permissive))
{
/* Lock CET if IBT or SHSTK is enabled in executable unless
IBT or SHSTK is enabled permissively. */
int res = dl_cet_lock_cet ();
if (res != 0)
_dl_fatal_printf ("%s: can't lock CET\n", program);
}
/* Set feature_1 if IBT or SHSTK is enabled in executable. */
cet_feature_changed = true;
}
#endif
if (cet_feature_changed)
{
unsigned int feature_1 = 0;
if (enable_ibt)
feature_1 |= GNU_PROPERTY_X86_FEATURE_1_IBT;
if (enable_shstk)
feature_1 |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
struct pthread *self = THREAD_SELF;
THREAD_SETMEM (self, header.feature_1, feature_1);
}
}
}
void
_dl_cet_open_check (struct link_map *l)
{
dl_cet_check (l, NULL);
}
#ifdef SHARED
# ifndef LINKAGE
# define LINKAGE
# endif
LINKAGE
void
_dl_cet_check (struct link_map *main_map, const char *program)
{
dl_cet_check (main_map, program);
}
#endif /* SHARED */
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