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glibc/sysdeps/x86/dl-cet.c
H.J. Lu edb5e0c8f9 x86/cet: Sync with Linux kernel 6.6 shadow stack interface 
Sync with Linux kernel 6.6 shadow stack interface.  Since only x86-64 is
supported, i386 shadow stack codes are unchanged and CET shouldn't be
enabled for i386.

1. When the shadow stack base in TCB is unset, the default shadow stack
is in use.  Use the current shadow stack pointer as the marker for the
default shadow stack. It is used to identify if the current shadow stack
is the same as the target shadow stack when switching ucontexts.  If yes,
INCSSP will be used to unwind shadow stack.  Otherwise, shadow stack
restore token will be used.
2. Allocate shadow stack with the map_shadow_stack syscall.  Since there
is no function to explicitly release ucontext, there is no place to
release shadow stack allocated by map_shadow_stack in ucontext functions.
Such shadow stacks will be leaked.
3. Rename arch_prctl CET commands to ARCH_SHSTK_XXX.
4. Rewrite the CET control functions with the current kernel shadow stack
interface.

Since CET is no longer enabled by kernel, a separate patch will enable
shadow stack during startup.
2024-01-01 05:22:48 -08:00

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/* x86 CET initializers function.
Copyright (C) 2018-2023 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/>. */
#include <unistd.h>
#include <errno.h>
#include <libintl.h>
#include <ldsodefs.h>
#include <dl-cet.h>
#include <sys/single_threaded.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
struct dl_cet_info
{
const char *program;
/* Check how IBT and SHSTK should be enabled. */
enum dl_x86_cet_control enable_ibt_type;
enum dl_x86_cet_control enable_shstk_type;
/* If IBT and SHSTK were previously enabled. */
unsigned int feature_1_enabled;
/* If IBT and SHSTK should be enabled. */
unsigned int enable_feature_1;
/* If there are any legacy shared object. */
unsigned int feature_1_legacy;
/* Which shared object is the first legacy shared object. */
unsigned int feature_1_legacy_ibt;
unsigned int feature_1_legacy_shstk;
};
/* Check if the object M and its dependencies are legacy object. */
static void
dl_check_legacy_object (struct link_map *m,
struct dl_cet_info *info)
{
unsigned int i;
struct link_map *l = NULL;
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 check for ld.so since it has the features enabled. The
features will be disabled later if they are not enabled in
executable. */
if (l == &GL(dl_rtld_map)
|| l->l_real == &GL(dl_rtld_map)
|| (info->program != NULL && l == m))
continue;
#endif
/* IBT and SHSTK set only if enabled in executable and all DSOs.
NB: cet_always_on is handled outside of the loop. */
info->enable_feature_1 &= ((l->l_x86_feature_1_and
& (GNU_PROPERTY_X86_FEATURE_1_IBT
| GNU_PROPERTY_X86_FEATURE_1_SHSTK))
| ~(GNU_PROPERTY_X86_FEATURE_1_IBT
| GNU_PROPERTY_X86_FEATURE_1_SHSTK));
if ((info->feature_1_legacy
& GNU_PROPERTY_X86_FEATURE_1_IBT) == 0
&& ((info->enable_feature_1
& GNU_PROPERTY_X86_FEATURE_1_IBT)
!= (info->feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_IBT)))
{
info->feature_1_legacy_ibt = i;
info->feature_1_legacy |= GNU_PROPERTY_X86_FEATURE_1_IBT;
}
if ((info->feature_1_legacy
& GNU_PROPERTY_X86_FEATURE_1_SHSTK) == 0
&& ((info->enable_feature_1
& GNU_PROPERTY_X86_FEATURE_1_SHSTK)
!= (info->feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_SHSTK)))
{
info->feature_1_legacy_shstk = i;
info->feature_1_legacy |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
}
}
/* Handle cet_always_on. */
if ((info->feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_IBT) != 0
&& info->enable_ibt_type == cet_always_on)
{
info->feature_1_legacy &= ~GNU_PROPERTY_X86_FEATURE_1_IBT;
info->enable_feature_1 |= GNU_PROPERTY_X86_FEATURE_1_IBT;
}
if ((info->feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0
&& info->enable_shstk_type == cet_always_on)
{
info->feature_1_legacy &= ~GNU_PROPERTY_X86_FEATURE_1_SHSTK;
info->enable_feature_1 |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
}
}
#ifdef SHARED
/* Enable IBT and SHSTK only if they are enabled in executable. Set
feature bits properly at the start of the program. */
static void
dl_cet_check_startup (struct link_map *m, struct dl_cet_info *info)
{
/* NB: IBT and SHSTK may be disabled by environment variable:
GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK.
*/
if (CPU_FEATURE_USABLE (IBT))
{
if (info->enable_ibt_type == cet_always_on)
info->enable_feature_1 |= GNU_PROPERTY_X86_FEATURE_1_IBT;
else
info->enable_feature_1 &= ((m->l_x86_feature_1_and
& GNU_PROPERTY_X86_FEATURE_1_IBT)
| ~GNU_PROPERTY_X86_FEATURE_1_IBT);
}
else
info->enable_feature_1 &= ~GNU_PROPERTY_X86_FEATURE_1_IBT;
if (CPU_FEATURE_USABLE (SHSTK))
{
if (info->enable_shstk_type == cet_always_on)
info->enable_feature_1 |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
else
info->enable_feature_1 &= ((m->l_x86_feature_1_and
& GNU_PROPERTY_X86_FEATURE_1_SHSTK)
| ~GNU_PROPERTY_X86_FEATURE_1_SHSTK);
}
else
info->enable_feature_1 &= ~GNU_PROPERTY_X86_FEATURE_1_SHSTK;
if (info->enable_feature_1 != 0)
dl_check_legacy_object (m, info);
unsigned int disable_feature_1
= info->enable_feature_1 ^ info->feature_1_enabled;
if (disable_feature_1 != 0)
{
/* Disable features in the kernel because of legacy objects or
cet_always_off. */
if (dl_cet_disable_cet (disable_feature_1) != 0)
_dl_fatal_printf ("%s: can't disable x86 Features\n",
info->program);
/* Clear the disabled bits. Sync dl_x86_feature_1 and
info->feature_1_enabled with info->enable_feature_1. */
info->feature_1_enabled = info->enable_feature_1;
GL(dl_x86_feature_1) = info->enable_feature_1;
}
if (HAS_CPU_FEATURE (IBT) || HAS_CPU_FEATURE (SHSTK))
{
/* Lock CET features only if IBT or SHSTK are enabled and are not
enabled permissively. */
unsigned int feature_1_lock = 0;
if (((info->feature_1_enabled & GNU_PROPERTY_X86_FEATURE_1_IBT)
!= 0)
&& info->enable_ibt_type != cet_permissive)
feature_1_lock |= GNU_PROPERTY_X86_FEATURE_1_IBT;
if (((info->feature_1_enabled & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
!= 0)
&& info->enable_shstk_type != cet_permissive)
feature_1_lock |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
if (feature_1_lock != 0
&& dl_cet_lock_cet (feature_1_lock) != 0)
_dl_fatal_printf ("%s: can't lock CET\n", info->program);
}
THREAD_SETMEM (THREAD_SELF, header.feature_1, GL(dl_x86_feature_1));
}
#endif
/* Check feature bits when dlopening the shared object M. */
static void
dl_cet_check_dlopen (struct link_map *m, struct dl_cet_info *info)
{
/* Check if there are any legacy objects loaded. */
if (info->enable_feature_1 != 0)
{
dl_check_legacy_object (m, info);
/* Skip if there are no legacy shared objects loaded. */
if (info->feature_1_legacy == 0)
return;
}
unsigned int disable_feature_1 = 0;
unsigned int legacy_obj = 0;
const char *msg = NULL;
if ((info->feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_IBT) != 0
&& (info->feature_1_legacy
& GNU_PROPERTY_X86_FEATURE_1_IBT) != 0)
{
/* Don't disable IBT if not single threaded since IBT may be still
enabled in other threads. */
if (info->enable_ibt_type != cet_permissive
|| !SINGLE_THREAD_P)
{
legacy_obj = info->feature_1_legacy_ibt;
msg = N_("rebuild shared object with IBT support enabled");
}
else
disable_feature_1 |= GNU_PROPERTY_X86_FEATURE_1_IBT;
}
/* Check the next feature only if there is no error. */
if (msg == NULL
&& (info->feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0
&& (info->feature_1_legacy
& GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0)
{
/* Don't disable SHSTK if not single threaded since SHSTK may be
still enabled in other threads. */
if (info->enable_shstk_type != cet_permissive
|| !SINGLE_THREAD_P)
{
legacy_obj = info->feature_1_legacy_shstk;
msg = N_("rebuild shared object with SHSTK support enabled");
}
else
disable_feature_1 |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
}
/* If there is an error, long jump back to the caller. */
if (msg != NULL)
_dl_signal_error (0, m->l_initfini[legacy_obj]->l_name, "dlopen",
msg);
if (disable_feature_1 != 0)
{
int res = dl_cet_disable_cet (disable_feature_1);
if (res)
{
if ((disable_feature_1
& GNU_PROPERTY_X86_FEATURE_1_IBT) != 0)
msg = N_("can't disable IBT");
else
msg = N_("can't disable SHSTK");
/* Long jump back to the caller on error. */
_dl_signal_error (-res, m->l_initfini[legacy_obj]->l_name,
"dlopen", msg);
}
/* Clear the disabled bits in dl_x86_feature_1. */
GL(dl_x86_feature_1) &= ~disable_feature_1;
THREAD_SETMEM (THREAD_SELF, header.feature_1,
GL(dl_x86_feature_1));
}
}
static void
dl_cet_check (struct link_map *m, const char *program)
{
struct dl_cet_info info;
/* Check how IBT and SHSTK should be enabled. */
info.enable_ibt_type = GL(dl_x86_feature_control).ibt;
info.enable_shstk_type = GL(dl_x86_feature_control).shstk;
info.feature_1_enabled = GL(dl_x86_feature_1);
/* No legacy object check if IBT and SHSTK are always on. */
if (info.enable_ibt_type == cet_always_on
&& info.enable_shstk_type == cet_always_on)
{
#ifdef SHARED
/* Set it only during startup. */
if (program != NULL)
THREAD_SETMEM (THREAD_SELF, header.feature_1,
info.feature_1_enabled);
#endif
return;
}
/* Check if IBT and SHSTK were enabled by kernel. */
if (info.feature_1_enabled == 0)
return;
info.program = program;
/* Check which features should be enabled. */
info.enable_feature_1 = 0;
if (info.enable_ibt_type != cet_always_off)
info.enable_feature_1 |= (info.feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_IBT);
if (info.enable_shstk_type != cet_always_off)
info.enable_feature_1 |= (info.feature_1_enabled
& GNU_PROPERTY_X86_FEATURE_1_SHSTK);
/* Start with no legacy objects. */
info.feature_1_legacy = 0;
info.feature_1_legacy_ibt = 0;
info.feature_1_legacy_shstk = 0;
#ifdef SHARED
if (program)
dl_cet_check_startup (m, &info);
else
#endif
dl_cet_check_dlopen (m, &info);
}
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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