sysdeps/i386/__longjmp.S

   1 /* longjmp for i386.
   2    Copyright (C) 1995-2022 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 #include <sysdep.h>
  20 #include <jmpbuf-offsets.h>
  21 #include <jmp_buf-ssp.h>
  22 #include <asm-syntax.h>
  23 #include <stap-probe.h>
  24
  25 /* Don't restore shadow stack register if
  26    1. Shadow stack isn't enabled.  Or
  27    2. __longjmp is defined for __longjmp_cancel.
  28  */
  29 #if !SHSTK_ENABLED || defined __longjmp
  30 # undef SHADOW_STACK_POINTER_OFFSET
  31 #endif
  32
  33         .text
  34 ENTRY (__longjmp)
  35 #ifdef PTR_DEMANGLE
  36         movl 4(%esp), %eax      /* User's jmp_buf in %eax.  */
  37
  38 # ifdef SHADOW_STACK_POINTER_OFFSET
  39 #  if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
  40         /* Check if Shadow Stack is enabled.  */
  41         testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
  42         jz L(skip_ssp)
  43 #  else
  44         xorl %edx, %edx
  45 #  endif
  46         /* Check and adjust the Shadow-Stack-Pointer.  */
  47         rdsspd %edx
  48         /* And compare it with the saved ssp value.  */
  49         subl SHADOW_STACK_POINTER_OFFSET(%eax), %edx
  50         je L(skip_ssp)
  51         /* Count the number of frames to adjust and adjust it
  52            with incssp instruction.  The instruction can adjust
  53            the ssp by [0..255] value only thus use a loop if
  54            the number of frames is bigger than 255.  */
  55         negl %edx
  56         shrl $2, %edx
  57         /* NB: We saved Shadow-Stack-Pointer of setjmp.  Since we are
  58                restoring Shadow-Stack-Pointer of setjmp's caller, we
  59                need to unwind shadow stack by one more frame.  */
  60         addl $1, %edx
  61         movl    $255, %ebx
  62 L(loop):
  63         cmpl    %ebx, %edx
  64         cmovb   %edx, %ebx
  65         incsspd %ebx
  66         subl    %ebx, %edx
  67         ja      L(loop)
  68 L(skip_ssp):
  69 # endif
  70         /* Save the return address now.  */
  71         movl (JB_PC*4)(%eax), %edx
  72         /* Get the stack pointer.  */
  73         movl (JB_SP*4)(%eax), %ecx
  74         PTR_DEMANGLE (%edx)
  75         PTR_DEMANGLE (%ecx)
  76         LIBC_PROBE (longjmp, 3, 4@%eax, -4@8(%esp), 4@%edx)
  77         cfi_def_cfa(%eax, 0)
  78         cfi_register(%eip, %edx)
  79         cfi_register(%esp, %ecx)
  80         cfi_offset(%ebx, JB_BX*4)
  81         cfi_offset(%esi, JB_SI*4)
  82         cfi_offset(%edi, JB_DI*4)
  83         cfi_offset(%ebp, JB_BP*4)
  84         /* Restore registers.  */
  85         movl (JB_BX*4)(%eax), %ebx
  86         movl (JB_SI*4)(%eax), %esi
  87         movl (JB_DI*4)(%eax), %edi
  88         movl (JB_BP*4)(%eax), %ebp
  89         cfi_restore(%ebx)
  90         cfi_restore(%esi)
  91         cfi_restore(%edi)
  92         cfi_restore(%ebp)
  93
  94         LIBC_PROBE (longjmp_target, 3, 4@%eax, -4@8(%esp), 4@%edx)
  95         movl 8(%esp), %eax      /* Second argument is return value.  */
  96         movl %ecx, %esp
  97 #else
  98         movl 4(%esp), %ecx      /* User's jmp_buf in %ecx.  */
  99         movl 8(%esp), %eax      /* Second argument is return value.  */
 100 # ifdef SHADOW_STACK_POINTER_OFFSET
 101 #  if IS_IN (libc) && defined SHARED
 102         /* Check if Shadow Stack is enabled.  */
 103         testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
 104         jz L(skip_ssp)
 105 #  endif
 106         /* Check and adjust the Shadow-Stack-Pointer.  */
 107         xorl %edx, %edx
 108         /* Get the current ssp.  */
 109         rdsspd  %edx
 110         /* And compare it with the saved ssp value.  */
 111         subl SHADOW_STACK_POINTER_OFFSET(%ecx), %edx
 112         je L(skip_ssp)
 113         /* Count the number of frames to adjust and adjust it
 114            with incssp instruction.  The instruction can adjust
 115            the ssp by [0..255] value only thus use a loop if
 116            the number of frames is bigger than 255.  */
 117         negl %edx
 118         shrl $2, %edx
 119         /* NB: We saved Shadow-Stack-Pointer of setjmp.  Since we are
 120                restoring Shadow-Stack-Pointer of setjmp's caller, we
 121                need to unwind shadow stack by one more frame.  */
 122         addl $1, %edx
 123         movl    $255, %ebx
 124 L(loop):
 125         cmpl    %ebx, %edx
 126         cmovb   %edx, %ebx
 127         incsspd %ebx
 128         subl    %ebx, %edx
 129         ja      L(loop)
 130 L(skip_ssp):
 131 # endif
 132         /* Save the return address now.  */
 133         movl (JB_PC*4)(%ecx), %edx
 134         LIBC_PROBE (longjmp, 3, 4@%ecx, -4@%eax, 4@%edx)
 135         /* Restore registers.  */
 136         movl (JB_BX*4)(%ecx), %ebx
 137         movl (JB_SI*4)(%ecx), %esi
 138         movl (JB_DI*4)(%ecx), %edi
 139         movl (JB_BP*4)(%ecx), %ebp
 140         movl (JB_SP*4)(%ecx), %esp
 141         LIBC_PROBE (longjmp_target, 3, 4@%ecx, -4@%ecx, 4@%edx)
 142 #endif
 143         /* Jump to saved PC.  */
 144         jmp *%edx
 145 END (__longjmp)