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94cd37ebb2
commit 04bba1e5d8
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Wed Aug 5 13:51:56 2020 -0700
x86: Set CPU usable feature bits conservatively [BZ #26552]
Set CPU usable feature bits only for CPU features which are usable in
user space and whose usability can be detected from user space, excluding
features like FSGSBASE whose enable bit can only be checked in the kernel.
no longer turns on the usable bits of IBT and SHSTK since we don't know
if IBT and SHSTK are usable until much later. Use HAS_CPU_FEATURE to
check if the processor supports IBT and SHSTK.
249 lines
7.1 KiB
C
249 lines
7.1 KiB
C
/* x86 CET initializers function.
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Copyright (C) 2018-2020 Free Software Foundation, Inc.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <unistd.h>
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#include <errno.h>
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#include <libintl.h>
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#include <ldsodefs.h>
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#include <dl-cet.h>
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/* GNU_PROPERTY_X86_FEATURE_1_IBT and GNU_PROPERTY_X86_FEATURE_1_SHSTK
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are defined in <elf.h>, which are only available for C sources.
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X86_FEATURE_1_IBT and X86_FEATURE_1_SHSTK are defined in <sysdep.h>
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which are available for both C and asm sources. They must match. */
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#if GNU_PROPERTY_X86_FEATURE_1_IBT != X86_FEATURE_1_IBT
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# error GNU_PROPERTY_X86_FEATURE_1_IBT != X86_FEATURE_1_IBT
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#endif
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#if GNU_PROPERTY_X86_FEATURE_1_SHSTK != X86_FEATURE_1_SHSTK
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# error GNU_PROPERTY_X86_FEATURE_1_SHSTK != X86_FEATURE_1_SHSTK
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#endif
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/* Check if object M is compatible with CET. */
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static void
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dl_cet_check (struct link_map *m, const char *program)
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{
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/* Check how IBT should be enabled. */
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enum dl_x86_cet_control enable_ibt_type
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= GL(dl_x86_feature_control).ibt;
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/* Check how SHSTK should be enabled. */
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enum dl_x86_cet_control enable_shstk_type
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= GL(dl_x86_feature_control).shstk;
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/* No legacy object check if both IBT and SHSTK are always on. */
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if (enable_ibt_type == cet_always_on
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&& enable_shstk_type == cet_always_on)
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return;
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/* Check if IBT is enabled by kernel. */
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bool ibt_enabled
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= (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
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/* Check if SHSTK is enabled by kernel. */
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bool shstk_enabled
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= (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
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if (ibt_enabled || shstk_enabled)
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{
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struct link_map *l = NULL;
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unsigned int ibt_legacy = 0, shstk_legacy = 0;
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bool found_ibt_legacy = false, found_shstk_legacy = false;
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/* Check if IBT and SHSTK are enabled in object. */
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bool enable_ibt = (ibt_enabled
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&& enable_ibt_type != cet_always_off);
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bool enable_shstk = (shstk_enabled
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&& enable_shstk_type != cet_always_off);
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if (program)
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{
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/* Enable IBT and SHSTK only if they are enabled in executable.
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NB: IBT and SHSTK may be disabled by environment variable:
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GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK
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*/
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enable_ibt &= (HAS_CPU_FEATURE (IBT)
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&& (enable_ibt_type == cet_always_on
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|| (m->l_cet & lc_ibt) != 0));
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enable_shstk &= (HAS_CPU_FEATURE (SHSTK)
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&& (enable_shstk_type == cet_always_on
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|| (m->l_cet & lc_shstk) != 0));
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}
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/* ld.so is CET-enabled by kernel. But shared objects may not
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support IBT nor SHSTK. */
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if (enable_ibt || enable_shstk)
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{
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unsigned int i;
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i = m->l_searchlist.r_nlist;
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while (i-- > 0)
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{
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/* Check each shared object to see if IBT and SHSTK are
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enabled. */
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l = m->l_initfini[i];
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if (l->l_init_called)
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continue;
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#ifdef SHARED
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/* Skip CET check for ld.so since ld.so is CET-enabled.
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CET will be disabled later if CET isn't enabled in
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executable. */
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if (l == &GL(dl_rtld_map)
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|| l->l_real == &GL(dl_rtld_map)
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|| (program && l == m))
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continue;
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#endif
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/* IBT is enabled only if it is enabled in executable as
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well as all shared objects. */
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enable_ibt &= (enable_ibt_type == cet_always_on
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|| (l->l_cet & lc_ibt) != 0);
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if (!found_ibt_legacy && enable_ibt != ibt_enabled)
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{
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found_ibt_legacy = true;
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ibt_legacy = i;
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}
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/* SHSTK is enabled only if it is enabled in executable as
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well as all shared objects. */
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enable_shstk &= (enable_shstk_type == cet_always_on
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|| (l->l_cet & lc_shstk) != 0);
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if (enable_shstk != shstk_enabled)
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{
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found_shstk_legacy = true;
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shstk_legacy = i;
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}
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}
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}
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bool cet_feature_changed = false;
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if (enable_ibt != ibt_enabled || enable_shstk != shstk_enabled)
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{
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if (!program)
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{
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if (enable_ibt_type != cet_permissive)
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{
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/* When IBT is enabled, we cannot dlopen a shared
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object without IBT. */
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if (found_ibt_legacy)
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_dl_signal_error (0,
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m->l_initfini[ibt_legacy]->l_name,
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"dlopen",
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N_("rebuild shared object with IBT support enabled"));
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}
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if (enable_shstk_type != cet_permissive)
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{
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/* When SHSTK is enabled, we cannot dlopen a shared
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object without SHSTK. */
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if (found_shstk_legacy)
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_dl_signal_error (0,
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m->l_initfini[shstk_legacy]->l_name,
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"dlopen",
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N_("rebuild shared object with SHSTK support enabled"));
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}
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if (enable_ibt_type != cet_permissive
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&& enable_shstk_type != cet_permissive)
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return;
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}
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/* Disable IBT and/or SHSTK if they are enabled by kernel, but
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disabled in executable or shared objects. */
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unsigned int cet_feature = 0;
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if (!enable_ibt)
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cet_feature |= GNU_PROPERTY_X86_FEATURE_1_IBT;
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if (!enable_shstk)
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cet_feature |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
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int res = dl_cet_disable_cet (cet_feature);
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if (res != 0)
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{
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if (program)
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_dl_fatal_printf ("%s: can't disable CET\n", program);
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else
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{
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if (found_ibt_legacy)
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l = m->l_initfini[ibt_legacy];
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else
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l = m->l_initfini[shstk_legacy];
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_dl_signal_error (-res, l->l_name, "dlopen",
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N_("can't disable CET"));
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}
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}
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/* Clear the disabled bits in dl_x86_feature_1. */
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GL(dl_x86_feature_1) &= ~cet_feature;
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cet_feature_changed = true;
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}
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#ifdef SHARED
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if (program && (ibt_enabled || shstk_enabled))
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{
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if ((!ibt_enabled
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|| enable_ibt_type != cet_permissive)
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&& (!shstk_enabled
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|| enable_shstk_type != cet_permissive))
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{
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/* Lock CET if IBT or SHSTK is enabled in executable unless
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IBT or SHSTK is enabled permissively. */
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int res = dl_cet_lock_cet ();
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if (res != 0)
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_dl_fatal_printf ("%s: can't lock CET\n", program);
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}
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/* Set feature_1 if IBT or SHSTK is enabled in executable. */
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cet_feature_changed = true;
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}
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#endif
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if (cet_feature_changed)
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{
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unsigned int feature_1 = 0;
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if (enable_ibt)
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feature_1 |= GNU_PROPERTY_X86_FEATURE_1_IBT;
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if (enable_shstk)
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feature_1 |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
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struct pthread *self = THREAD_SELF;
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THREAD_SETMEM (self, header.feature_1, feature_1);
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}
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}
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}
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void
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_dl_cet_open_check (struct link_map *l)
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{
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dl_cet_check (l, NULL);
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}
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#ifdef SHARED
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# ifndef LINKAGE
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# define LINKAGE
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# endif
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LINKAGE
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void
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_dl_cet_check (struct link_map *main_map, const char *program)
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{
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dl_cet_check (main_map, program);
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}
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#endif /* SHARED */
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