sysdeps/unix/sysv/linux/x86_64/__start_context.S

   1 /* Copyright (C) 2002-2019 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Andreas Jaeger <aj@suse.de>, 2002.
   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
  21 #if SHSTK_ENABLED
  22 # include <asm/prctl.h>
  23 # include "ucontext_i.h"
  24
  25 /* Use CALL to push __start_context onto the new stack as well as the new
  26    shadow stack.  RDI points to ucontext:
  27    Incoming:
  28      __ssp[0]: The original caller's shadow stack pointer.
  29      __ssp[1]: The size of the new shadow stack.
  30      __ssp[2]: The size of the new shadow stack.
  31    Outgoing:
  32      __ssp[0]: The new shadow stack pointer.
  33      __ssp[1]: The base address of the new shadow stack.
  34      __ssp[2]: The size of the new shadow stack.
  35  */
  36
  37 ENTRY(__push___start_context)
  38         /* Save the pointer to ucontext.  */
  39         movq    %rdi, %r9
  40         /* Get the original shadow stack pointer.  */
  41         rdsspq  %r8
  42         /* Save the original stack pointer.  */
  43         movq    %rsp, %rdx
  44         /* Load the top of the new stack into RSI.  */
  45         movq    oRSP(%rdi), %rsi
  46         /* Add 8 bytes to RSI since CALL will push the 8-byte return
  47            address onto stack.  */
  48         leaq    8(%rsi), %rsp
  49         /* Allocate the new shadow stack.  The size of the new shadow
  50            stack is passed in __ssp[1].  */
  51         lea     (oSSP + 8)(%rdi), %RSI_LP
  52         movl    $ARCH_CET_ALLOC_SHSTK, %edi
  53         movl    $__NR_arch_prctl, %eax
  54         /* The new shadow stack base is returned in __ssp[1].  */
  55         syscall
  56         testq   %rax, %rax
  57         jne     L(hlt)          /* This should never happen.  */
  58
  59         /* Get the size of the new shadow stack.  */
  60         movq    8(%rsi), %rdi
  61
  62         /* Get the base address of the new shadow stack.  */
  63         movq    (%rsi), %rsi
  64
  65         /* Use the restore stoken to restore the new shadow stack.  */
  66         rstorssp -8(%rsi, %rdi)
  67
  68         /* Save the restore token on the original shadow stack.  */
  69         saveprevssp
  70
  71         /* Push the address of "jmp __start_context" onto the new stack
  72            as well as the new shadow stack.  */
  73         call    1f
  74         jmp     __start_context
  75 1:
  76
  77         /* Get the new shadow stack pointer.  */
  78         rdsspq  %rdi
  79
  80         /* Use the restore stoken to restore the original shadow stack.  */
  81         rstorssp -8(%r8)
  82
  83         /* Save the restore token on the new shadow stack.  */
  84         saveprevssp
  85
  86         /* Store the new shadow stack pointer in __ssp[0].  */
  87         movq    %rdi, oSSP(%r9)
  88
  89         /* Restore the original stack.  */
  90         mov     %rdx, %rsp
  91         ret
  92 END(__push___start_context)
  93 #endif
  94
  95 /* This is the helper code which gets called if a function which is
  96    registered with 'makecontext' returns.  In this case we have to
  97    install the context listed in the uc_link element of the context
  98    'makecontext' manipulated at the time of the 'makecontext' call.
  99    If the pointer is NULL the process must terminate.  */
 100
 101
 102 ENTRY(__start_context)
 103         /* This removes the parameters passed to the function given to
 104            'makecontext' from the stack.  RBX contains the address
 105            on the stack pointer for the next context.  */
 106         movq    %rbx, %rsp
 107
 108         /* Don't use pop here so that stack is aligned to 16 bytes.  */
 109         movq    (%rsp), %rdi            /* This is the next context.  */
 110         testq   %rdi, %rdi
 111         je      2f                      /* If it is zero exit.  */
 112
 113         call    __setcontext
 114         /* If this returns (which can happen if the syscall fails) we'll
 115            exit the program with the return error value (-1).  */
 116         movq    %rax,%rdi
 117
 118 2:
 119         call    HIDDEN_JUMPTARGET(exit)
 120         /* The 'exit' call should never return.  In case it does cause
 121            the process to terminate.  */
 122 L(hlt):
 123         hlt
 124 END(__start_context)