sysdeps/x86_64/libc-start.h

   1 /* x86-64 definitions for libc main startup.
   2    Copyright (C) 2018-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #ifndef SHARED
  20 # define ARCH_SETUP_IREL() apply_irel ()
  21 # define ARCH_APPLY_IREL()
  22 # ifdef __CET__
  23 /* Get CET features enabled in the static executable.  */
  24
  25 static inline unsigned int
  26 get_cet_feature (void)
  27 {
  28   /* Check if CET is supported and not disabled by tunables.  */
  29   const struct cpu_features *cpu_features = __get_cpu_features ();
  30   unsigned int cet_feature = 0;
  31   if (CPU_FEATURE_USABLE_P (cpu_features, IBT))
  32     cet_feature |= GNU_PROPERTY_X86_FEATURE_1_IBT;
  33   if (CPU_FEATURE_USABLE_P (cpu_features, SHSTK))
  34     cet_feature |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
  35   if (!cet_feature)
  36     return cet_feature;
  37
  38   struct link_map *main_map = _dl_get_dl_main_map ();
  39
  40   /* Scan program headers backward to check PT_GNU_PROPERTY early for
  41      x86 feature bits on static executable.  */
  42   const ElfW(Phdr) *phdr = GL(dl_phdr);
  43   const ElfW(Phdr) *ph;
  44   for (ph = phdr + GL(dl_phnum); ph != phdr; ph--)
  45     if (ph[-1].p_type == PT_GNU_PROPERTY)
  46       {
  47         _dl_process_pt_gnu_property (main_map, -1, &ph[-1]);
  48         /* Enable IBT and SHSTK only if they are enabled on static
  49            executable.  */
  50         cet_feature &= (main_map->l_x86_feature_1_and
  51                         & (GNU_PROPERTY_X86_FEATURE_1_IBT
  52                            | GNU_PROPERTY_X86_FEATURE_1_SHSTK));
  53         /* Set GL(dl_x86_feature_1) to the enabled CET features.  */
  54         GL(dl_x86_feature_1) = cet_feature;
  55         break;
  56       }
  57
  58   return cet_feature;
  59 }
  60
  61 /* The function using this macro to enable shadow stack must not return
  62    to avoid shadow stack underflow.  */
  63 #  define ARCH_SETUP_TLS()                                              \
  64   {                                                                     \
  65     __libc_setup_tls ();                                                \
  66                                                                         \
  67     unsigned int cet_feature = get_cet_feature ();                      \
  68     ENABLE_X86_CET (cet_feature);                                       \
  69     _dl_cet_setup_features (cet_feature);                               \
  70   }
  71 # else
  72 #  define ARCH_SETUP_TLS()      __libc_setup_tls ()
  73 # endif
  74 #endif /* !SHARED */