/* Save current context and install the given one. 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(__swapcontext) /* Load address of the context data structure we save in. */ movl 4(%esp), %eax /* Save the preserved register values and the return address. */ movl %edi, oEDI(%eax) movl %esi, oESI(%eax) movl %ebp, oEBP(%eax) movl (%esp), %ecx movl %ecx, oEIP(%eax) leal 4(%esp), %ecx movl %ecx, oESP(%eax) movl %ebx, oEBX(%eax) /* Save the FS segment register. */ xorl %edx, %edx movw %fs, %dx movl %edx, oFS(%eax) /* We have separate floating-point register content memory on the stack. We use the __fpregs_mem block in the context. Set the links up correctly. */ leal oFPREGSMEM(%eax), %ecx movl %ecx, oFPREGS(%eax) /* Save the floating-point context. */ fnstenv (%ecx) /* Load address of the context data structure we have to load. */ movl 8(%esp), %ecx /* Save the current signal mask and install the new one. */ pushl %ebx leal oSIGMASK(%eax), %edx leal oSIGMASK(%ecx), %ecx movl $SIG_SETMASK, %ebx movl $__NR_sigprocmask, %eax ENTER_KERNEL popl %ebx cmpl $-4095, %eax /* Check %eax for error. */ jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */ /* EAX was modified, reload it. */ movl 8(%esp), %eax /* Restore the floating-point context. Not the registers, only the rest. */ movl oFPREGS(%eax), %ecx fldenv (%ecx) /* Restore the FS segment register. We don't touch the GS register since it is used for threads. */ movl oFS(%eax), %edx movw %dx, %fs #if SHSTK_ENABLED /* Check if Shadow Stack is enabled. */ testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET jz L(no_shstk) xorl %eax, %eax cmpl %gs:SSP_BASE_OFFSET, %eax jnz L(shadow_stack_bound_recorded) /* Get the base address and size of the default shadow stack which must be the current shadow stack since nothing has been recorded yet. */ sub $24, %esp mov %esp, %ecx movl $ARCH_CET_STATUS, %ebx movl $__NR_arch_prctl, %eax ENTER_KERNEL testl %eax, %eax jz L(continue_no_err) /* This should never happen. */ hlt L(continue_no_err): /* Record the base of the current shadow stack. */ movl 8(%esp), %eax movl %eax, %gs:SSP_BASE_OFFSET add $24, %esp L(shadow_stack_bound_recorded): /* Load address of the context data structure we save in. */ movl 4(%esp), %eax /* Load address of the context data structure we swap in */ movl 8(%esp), %edx /* If we unwind the stack, we can't undo stack unwinding. Just save the target shadow stack pointer as the current shadow stack pointer. */ movl oSSP(%edx), %ecx movl %ecx, oSSP(%eax) /* Save the current shadow stack base in ucontext. */ movl %gs:SSP_BASE_OFFSET, %ecx movl %ecx, (oSSP + 4)(%eax) /* If the base of the target shadow stack is the same as the base of the current shadow stack, we unwind the shadow stack. Otherwise it is a stack switch and we look for a restore token. */ movl oSSP(%edx), %esi movl %esi, %edi /* Get the base of the target shadow stack. */ movl (oSSP + 4)(%edx), %ecx cmpl %gs:SSP_BASE_OFFSET, %ecx je L(unwind_shadow_stack) /* Align the saved original shadow stack pointer to the next 8 byte aligned boundary. */ andl $-8, %esi L(find_restore_token_loop): /* Look for a restore token. */ movl -8(%esi), %ebx andl $-8, %ebx cmpl %esi, %ebx je L(restore_shadow_stack) /* Try the next slot. */ subl $8, %esi jmp L(find_restore_token_loop) L(restore_shadow_stack): /* The target shadow stack will be restored. Save the current shadow stack pointer. */ rdsspd %ecx movl %ecx, oSSP(%eax) /* Use the restore stoken to restore the target shadow stack. */ rstorssp -8(%esi) /* Save the restore token on the old shadow stack. NB: This restore token may be checked by setcontext or swapcontext later. */ saveprevssp /* Record the new shadow stack base that was switched to. */ movl (oSSP + 4)(%edx), %ebx movl %ebx, %gs:SSP_BASE_OFFSET L(unwind_shadow_stack): rdsspd %ebx subl %edi, %ebx je L(skip_unwind_shadow_stack) negl %ebx shrl $2, %ebx movl $255, %esi L(loop): cmpl %esi, %ebx cmovb %ebx, %esi incsspd %esi subl %esi, %ebx ja L(loop) L(skip_unwind_shadow_stack): /* Load the new stack pointer. */ movl oESP(%edx), %esp /* Load the values of all the preserved registers (except ESP). */ movl oEDI(%edx), %edi movl oESI(%edx), %esi movl oEBP(%edx), %ebp movl oEBX(%edx), %ebx /* Get the return address set with getcontext. */ movl oEIP(%edx), %ecx /* Check if return address is valid for the case when setcontext is invoked from L(exitcode) with linked context. */ rdsspd %eax cmpl (%eax), %ecx /* Clear EAX to indicate success. NB: Don't use xorl to keep EFLAGS for jne. */ movl $0, %eax jne L(jmp) /* Return to the new context if return address valid. */ pushl %ecx ret L(jmp): /* Jump to the new context directly. */ jmp *%ecx L(no_shstk): #endif /* Fetch the address to return to. */ movl oEIP(%eax), %ecx /* Load the new stack pointer. */ movl oESP(%eax), %esp /* Push the return address on the new stack so we can return there. */ pushl %ecx /* Load the values of all the preserved registers (except ESP). */ movl oEDI(%eax), %edi movl oESI(%eax), %esi movl oEBP(%eax), %ebp movl oEBX(%eax), %ebx /* All done, return 0 for success. */ xorl %eax, %eax /* The following 'ret' will pop the address of the code and jump to it. */ ret PSEUDO_END(__swapcontext) weak_alias (__swapcontext, swapcontext)