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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>
#include <cet-tunables.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
static int
dl_cet_mark_legacy_region (struct link_map *l)
{
/* Mark PT_LOAD segments with PF_X in legacy code page bitmap. */
size_t i, phnum = l->l_phnum;
const ElfW(Phdr) *phdr = l->l_phdr;
#ifdef __x86_64__
typedef unsigned long long word_t;
#else
typedef unsigned long word_t;
#endif
unsigned int bits_to_set;
word_t mask_to_set;
#define BITS_PER_WORD (sizeof (word_t) * 8)
#define BITMAP_FIRST_WORD_MASK(start) \
(~((word_t) 0) << ((start) & (BITS_PER_WORD - 1)))
#define BITMAP_LAST_WORD_MASK(nbits) \
(~((word_t) 0) >> (-(nbits) & (BITS_PER_WORD - 1)))
word_t *bitmap = (word_t *) GL(dl_x86_legacy_bitmap)[0];
word_t bitmap_size = GL(dl_x86_legacy_bitmap)[1];
word_t *p;
size_t page_size = GLRO(dl_pagesize);
for (i = 0; i < phnum; i++)
if (phdr[i].p_type == PT_LOAD && (phdr[i].p_flags & PF_X))
{
/* One bit in legacy bitmap represents a page. */
ElfW(Addr) start = (phdr[i].p_vaddr + l->l_addr) / page_size;
ElfW(Addr) len = (phdr[i].p_memsz + page_size - 1) / page_size;
ElfW(Addr) end = start + len;
if ((end / 8) > bitmap_size)
return -EINVAL;
p = bitmap + (start / BITS_PER_WORD);
bits_to_set = BITS_PER_WORD - (start % BITS_PER_WORD);
mask_to_set = BITMAP_FIRST_WORD_MASK (start);
while (len >= bits_to_set)
{
*p |= mask_to_set;
len -= bits_to_set;
bits_to_set = BITS_PER_WORD;
mask_to_set = ~((word_t) 0);
p++;
}
if (len)
{
mask_to_set &= BITMAP_LAST_WORD_MASK (end);
*p |= mask_to_set;
}
}
return 0;
}
/* 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. */
unsigned int enable_ibt_type
= GL(dl_x86_feature_1)[1] & ((1 << CET_MAX) - 1);
/* Check how SHSTK should be enabled. */
unsigned int enable_shstk_type
= ((GL(dl_x86_feature_1)[1] >> CET_MAX) & ((1 << CET_MAX) - 1));
/* 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)[0] & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
/* Check if SHSTK is enabled by kernel. */
bool shstk_enabled
= (GL(dl_x86_feature_1)[0] & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
if (ibt_enabled || shstk_enabled)
{
struct link_map *l = NULL;
/* 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 &= (HAS_CPU_FEATURE (IBT)
&& (enable_ibt_type == CET_ALWAYS_ON
|| (m->l_cet & lc_ibt) != 0));
enable_shstk &= (HAS_CPU_FEATURE (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)
{
int res;
unsigned int i;
unsigned int first_legacy, last_legacy;
bool need_legacy_bitmap = false;
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
if (enable_ibt
&& enable_ibt_type != CET_ALWAYS_ON
&& !(l->l_cet & lc_ibt))
{
/* Remember the first and last legacy objects. */
if (!need_legacy_bitmap)
last_legacy = i;
first_legacy = i;
need_legacy_bitmap = true;
}
/* 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 (need_legacy_bitmap)
{
if (GL(dl_x86_legacy_bitmap)[0])
{
/* Change legacy bitmap to writable. */
if (__mprotect ((void *) GL(dl_x86_legacy_bitmap)[0],
GL(dl_x86_legacy_bitmap)[1],
PROT_READ | PROT_WRITE) < 0)
{
mprotect_failure:
if (program)
_dl_fatal_printf ("%s: mprotect legacy bitmap failed\n",
l->l_name);
else
_dl_signal_error (EINVAL, l->l_name, "dlopen",
N_("mprotect legacy bitmap failed"));
}
}
else
{
/* Allocate legacy bitmap. */
int res = dl_cet_allocate_legacy_bitmap
(GL(dl_x86_legacy_bitmap));
if (res != 0)
{
if (program)
_dl_fatal_printf ("%s: legacy bitmap isn't available\n",
l->l_name);
else
_dl_signal_error (EINVAL, l->l_name, "dlopen",
N_("legacy bitmap isn't available"));
}
}
/* Put legacy shared objects in legacy bitmap. */
for (i = first_legacy; i <= last_legacy; i++)
{
l = m->l_initfini[i];
if (l->l_init_called || (l->l_cet & lc_ibt))
continue;
#ifdef SHARED
if (l == &GL(dl_rtld_map)
|| l->l_real == &GL(dl_rtld_map)
|| (program && l == m))
continue;
#endif
/* If IBT is enabled in executable and IBT isn't enabled
in this shard object, mark PT_LOAD segments with PF_X
in legacy code page bitmap. */
res = dl_cet_mark_legacy_region (l);
if (res != 0)
{
if (program)
_dl_fatal_printf ("%s: failed to mark legacy code region\n",
l->l_name);
else
_dl_signal_error (-res, l->l_name, "dlopen",
N_("failed to mark legacy code region"));
}
}
/* Change legacy bitmap to read-only. */
if (__mprotect ((void *) GL(dl_x86_legacy_bitmap)[0],
GL(dl_x86_legacy_bitmap)[1], PROT_READ) < 0)
goto mprotect_failure;
}
}
bool cet_feature_changed = false;
if (enable_ibt != ibt_enabled || enable_shstk != shstk_enabled)
{
if (!program
&& enable_shstk_type != CET_PERMISSIVE)
{
/* When SHSTK is enabled, we can't dlopening a shared
object without SHSTK. */
if (enable_shstk != shstk_enabled)
_dl_signal_error (EINVAL, l->l_name, "dlopen",
N_("shadow stack isn't enabled"));
return;
}
/* Disable IBT and/or SHSTK if they are enabled by kernel, but
disabled in executable or shared objects. */
unsigned int cet_feature = 0;
/* Disable IBT only during program startup. */
if (program && !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
_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)[0] &= ~cet_feature;
cet_feature_changed = true;
}
#ifdef SHARED
if (program
&& (!shstk_enabled
|| enable_shstk_type != CET_PERMISSIVE)
&& (ibt_enabled || shstk_enabled))
{
/* Lock CET if IBT or SHSTK is enabled in executable. Don't
lock CET if SHSTK is enabled permissively. */
int res = dl_cet_lock_cet ();
if (res != 0)
_dl_fatal_printf ("%s: can't lock CET\n", program);
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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