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/* x86 CET initializers function.
Copyright (C) 2018-2021 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)
{
THREAD_SETMEM (THREAD_SELF, header.feature_1, GL(dl_x86_feature_1));
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_x86_feature_1_and
& GNU_PROPERTY_X86_FEATURE_1_IBT) != 0));
enable_shstk &= (CPU_FEATURE_USABLE (SHSTK)
&& (enable_shstk_type == cet_always_on
|| (m->l_x86_feature_1_and
& GNU_PROPERTY_X86_FEATURE_1_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_x86_feature_1_and
& GNU_PROPERTY_X86_FEATURE_1_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_x86_feature_1_and
& GNU_PROPERTY_X86_FEATURE_1_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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