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/* Save current context and install the given one.
Copyright (C) 2001-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
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
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <asm/prctl.h>
#include "ucontext_i.h"
ENTRY(__swapcontext)
/* Load address of the context data structure we save in. */
movl 4(%esp), %eax
/* Return value of swapcontext. EAX is the only register whose
value is not preserved. */
movl $0, oEAX(%eax)
/* Save the 32-bit register values and the return address. */
movl %ecx, oECX(%eax)
movl %edx, oEDX(%eax)
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 32-bit registers (except ESP).
Since we are loading from EAX, it must be last. */
movl oEDI(%eax), %edi
movl oESI(%eax), %esi
movl oEBP(%eax), %ebp
movl oEBX(%eax), %ebx
movl oEDX(%eax), %edx
movl oECX(%eax), %ecx
movl oEAX(%eax), %eax
/* The following 'ret' will pop the address of the code and jump
to it. */
ret
PSEUDO_END(__swapcontext)
weak_alias (__swapcontext, swapcontext)
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