/* Create new context. Copyright (C) 2001-2018 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Ulrich Drepper , 2001. 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 . */ #include #include #include "ucontext_i.h" ENTRY(__makecontext) movl 4(%esp), %eax /* Load the address of the function we are supposed to run. */ movl 8(%esp), %ecx /* Compute the address of the stack. The information comes from to us_stack element. */ movl oSS_SP(%eax), %edx movl %ecx, oEIP(%eax) addl oSS_SIZE(%eax), %edx /* Remember the number of parameters for the exit handler since it has to remove them. We store the number in the EBX register which the function we will call must preserve. */ movl 12(%esp), %ecx movl %ecx, oEBX(%eax) /* Make room on the new stack for the parameters. Room for the arguments, return address (== L(exitcode)) and oLINK pointer is needed. One of the pointer sizes is subtracted after aligning the stack. */ negl %ecx leal -4(%edx,%ecx,4), %edx negl %ecx /* Align the stack. */ andl $0xfffffff0, %edx subl $4, %edx /* Store the future stack pointer. */ movl %edx, oESP(%eax) /* Put the next context on the new stack (from the uc_link element). */ movl oLINK(%eax), %eax movl %eax, 4(%edx,%ecx,4) /* Copy all the parameters. */ jecxz 2f 1: movl 12(%esp,%ecx,4), %eax movl %eax, (%edx,%ecx,4) decl %ecx jnz 1b 2: #if SHSTK_ENABLED /* Check if Shadow Stack is enabled. */ testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET jz L(skip_ssp) /* Reload the pointer to ucontext. */ movl 4(%esp), %eax /* Shadow stack is enabled. We need to allocate a new shadow stack. */ subl oSS_SP(%eax), %edx shrl $STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT, %edx /* Align shadow stack size to 8 bytes. */ addl $7, %edx andl $-8, %edx /* Store shadow stack size in __ssp[2]. */ movl %edx, (oSSP + 8)(%eax) /* Save ESI in the second scratch register slot. */ movl %esi, oSCRATCH2(%eax) /* Save EDI in the third scratch register slot. */ movl %edi, oSCRATCH3(%eax) /* Save the pointer to ucontext. */ movl %eax, %edi /* Get the original shadow stack pointer. */ rdsspd %esi /* Align the saved original shadow stack pointer to the next 8 byte aligned boundary. */ andl $-8, %esi /* Load the top of the new stack into EDX. */ movl oESP(%eax), %edx /* We need to terminate the FDE here because the unwinder looks at ra-1 for unwind information. */ cfi_endproc /* Swap the original stack pointer with the top of the new stack. */ xchgl %esp, %edx /* Add 4 bytes since CALL will push the 4-byte return address onto stack. */ addl $4, %esp /* Allocate the new shadow stack. Save EBX in the first scratch register slot. */ movl %ebx, oSCRATCH1(%eax) /* CET syscall takes 64-bit sizes. */ subl $16, %esp movl (oSSP + 8)(%eax), %ecx movl %ecx, (%esp) movl $0, 4(%esp) movl %ecx, 8(%esp) movl $0, 12(%esp) movl %esp, %ecx movl $ARCH_CET_ALLOC_SHSTK, %ebx movl $__NR_arch_prctl, %eax ENTER_KERNEL testl %eax, %eax jne L(hlt) /* This should never happen. */ /* Copy the base address of the new shadow stack to __ssp[1]. */ movl (%esp), %eax movl %eax, (oSSP + 4)(%edi) addl $16, %esp /* Restore EBX from the first scratch register slot. */ movl oSCRATCH1(%edi), %ebx /* Get the size of the new shadow stack. */ movl (oSSP + 8)(%edi), %ecx /* Use the restore stoken to restore the new shadow stack. */ rstorssp -8(%eax, %ecx) /* Save the restore token at the next 8 byte aligned boundary on the original shadow stack. */ saveprevssp /* Push the address of "jmp exitcode" onto the new stack as well as the new shadow stack. */ call 1f jmp L(exitcode) 1: /* Get the new shadow stack pointer. */ rdsspd %eax /* Use the restore stoken to restore the original shadow stack. */ rstorssp -8(%esi) /* Save the restore token on the new shadow stack. */ saveprevssp /* Store the new shadow stack pointer in __ssp[0]. */ movl %eax, oSSP(%edi) /* Restore the original stack. */ mov %edx, %esp cfi_startproc /* Restore ESI from the second scratch register slot. */ movl oSCRATCH2(%edi), %esi /* Restore EDI from the third scratch register slot. */ movl oSCRATCH3(%edi), %edi ret L(skip_ssp): #endif /* If the function we call returns we must continue with the context which is given in the uc_link element. To do this set the return address for the function the user provides to a little bit of helper code which does the magic (see below). */ #ifdef PIC call 1f cfi_adjust_cfa_offset (4) 1: popl %ecx cfi_adjust_cfa_offset (-4) addl $L(exitcode)-1b, %ecx movl %ecx, (%edx) #else movl $L(exitcode), (%edx) #endif /* We need to terminate the FDE here instead of after ret because the unwinder looks at ra-1 for unwind information. */ cfi_endproc /* 'makecontext' returns no value. */ ret /* This is the helper code which gets called if a function which is registered with 'makecontext' returns. In this case we have to install the context listed in the uc_link element of the context 'makecontext' manipulated at the time of the 'makecontext' call. If the pointer is NULL the process must terminate. */ L(exitcode): /* This removes the parameters passed to the function given to 'makecontext' from the stack. EBX contains the number of parameters (see above). */ leal (%esp,%ebx,4), %esp cmpl $0, (%esp) /* Check the next context. */ je 2f /* If it is zero exit. */ call HIDDEN_JUMPTARGET(__setcontext) /* If this returns (which can happen if the syscall fails) we'll exit the program with the return error value (-1). */ jmp L(call_exit) 2: /* Exit with status 0. */ xorl %eax, %eax L(call_exit): /* Align the stack and pass the exit code (from %eax). */ andl $0xfffffff0, %esp subl $12, %esp pushl %eax call HIDDEN_JUMPTARGET(exit) /* The 'exit' call should never return. In case it does cause the process to terminate. */ L(hlt): hlt cfi_startproc END(__makecontext) weak_alias (__makecontext, makecontext)