sysdeps/unix/sysv/linux/x86_64/dl-cet.h

   1 /* Linux/x86-64 CET initializers function.
   2    Copyright (C) 2023-2024 Free Software Foundation, Inc.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <sys/prctl.h>
  19 #include <asm/prctl.h>
  20 #include <features-offsets.h>
  21
  22 static __always_inline int
  23 dl_cet_disable_cet (unsigned int cet_feature)
  24 {
  25   if (cet_feature != GNU_PROPERTY_X86_FEATURE_1_SHSTK)
  26     return -1;
  27   long long int kernel_feature = ARCH_SHSTK_SHSTK;
  28   return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_DISABLE,
  29                                       kernel_feature);
  30 }
  31
  32 static __always_inline int
  33 dl_cet_lock_cet (unsigned int cet_feature)
  34 {
  35   if (cet_feature != GNU_PROPERTY_X86_FEATURE_1_SHSTK)
  36     return -1;
  37   /* Lock all SHSTK features.  */
  38   long long int kernel_feature = -1;
  39   return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_LOCK,
  40                                       kernel_feature);
  41 }
  42
  43 static __always_inline unsigned int
  44 dl_cet_get_cet_status (void)
  45 {
  46   unsigned long long kernel_feature;
  47   unsigned int status = 0;
  48   if (INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_STATUS,
  49                              &kernel_feature) == 0)
  50     {
  51       if ((kernel_feature & ARCH_SHSTK_SHSTK) != 0)
  52         status = GNU_PROPERTY_X86_FEATURE_1_SHSTK;
  53     }
  54   return status;
  55 }
  56
  57 static __always_inline bool
  58 dl_cet_ibt_enabled (void)
  59 {
  60   unsigned int feature_1 = THREAD_GETMEM (THREAD_SELF,
  61                                           header.feature_1);
  62   return (feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
  63 }
  64
  65 /* Enable shadow stack with a macro to avoid shadow stack underflow.  */
  66 #define ENABLE_X86_CET(cet_feature)                             \
  67   if ((cet_feature & GNU_PROPERTY_X86_FEATURE_1_SHSTK))         \
  68     {                                                           \
  69       long long int kernel_feature = ARCH_SHSTK_SHSTK;          \
  70       INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_ENABLE,     \
  71                              kernel_feature);                   \
  72     }
  73
  74 #define X86_STRINGIFY_1(x)      #x
  75 #define X86_STRINGIFY(x)        X86_STRINGIFY_1 (x)
  76
  77 /* Enable shadow stack before calling _dl_init if it is enabled in
  78    GL(dl_x86_feature_1).  Call _dl_setup_x86_features to setup shadow
  79    stack.  */
  80 #define RTLD_START_ENABLE_X86_FEATURES \
  81 "\
  82         # Check if shadow stack is enabled in GL(dl_x86_feature_1).\n\
  83         movl _rtld_local+" X86_STRINGIFY (RTLD_GLOBAL_DL_X86_FEATURE_1_OFFSET) "(%rip), %edx\n\
  84         testl $" X86_STRINGIFY (X86_FEATURE_1_SHSTK) ", %edx\n\
  85         jz 1f\n\
  86         # Enable shadow stack if enabled in GL(dl_x86_feature_1).\n\
  87         movl $" X86_STRINGIFY (ARCH_SHSTK_SHSTK) ", %esi\n\
  88         movl $" X86_STRINGIFY (ARCH_SHSTK_ENABLE) ", %edi\n\
  89         movl $" X86_STRINGIFY (__NR_arch_prctl) ", %eax\n\
  90         syscall\n\
  91 1:\n\
  92         # Pass GL(dl_x86_feature_1) to _dl_cet_setup_features.\n\
  93         movl %edx, %edi\n\
  94         # Align stack for the _dl_cet_setup_features call.\n\
  95         andq $-16, %rsp\n\
  96         call _dl_cet_setup_features\n\
  97         # Restore %rax and %rsp from %r12 and %r13.\n\
  98         movq %r12, %rax\n\
  99         movq %r13, %rsp\n\
 100 "