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/* Install given context.
Copyright (C) 2001-2024 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(__setcontext)
/* Load address of the context data structure. */
movl 4(%esp), %eax
/* Get the current signal mask. Note that we preserve EBX in case
the system call fails and we return from the function with an
error. */
pushl %ebx
cfi_adjust_cfa_offset (4)
xorl %edx, %edx
leal oSIGMASK(%eax), %ecx
movl $SIG_SETMASK, %ebx
cfi_rel_offset (ebx, 0)
movl $__NR_sigprocmask, %eax
ENTER_KERNEL
popl %ebx
cfi_adjust_cfa_offset (-4)
cfi_restore (ebx)
cmpl $-4095, %eax /* Check %eax for error. */
jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
/* EAX was modified, reload it. */
movl 4(%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), %ecx
movw %cx, %fs
/* Load the new stack pointer. */
cfi_def_cfa (eax, 0)
cfi_offset (edi, oEDI)
cfi_offset (esi, oESI)
cfi_offset (ebp, oEBP)
cfi_offset (ebx, oEBX)
movl oESP(%eax), %esp
#if SHSTK_ENABLED
/* Check if Shadow Stack is enabled. */
testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
jz L(no_shstk)
/* 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(%eax), %esi
movl %esi, %edi
/* Get the base of the target shadow stack. */
movl (oSSP + 4)(%eax), %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):
/* Pop return address from the shadow stack since setcontext
will not return. */
movl $1, %ebx
incsspd %ebx
/* 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)(%eax), %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 values of all the preserved registers (except ESP). */
movl oEDI(%eax), %edi
movl oESI(%eax), %esi
movl oEBP(%eax), %ebp
movl oEBX(%eax), %ebx
/* Get the return address set with getcontext. */
movl oEIP(%eax), %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
/* 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
/* End FDE here, we fall into another context. */
cfi_endproc
cfi_startproc
/* The following 'ret' will pop the address of the code and jump
to it. */
ret
PSEUDO_END(__setcontext)
libc_hidden_def (__setcontext)
weak_alias (__setcontext, setcontext)
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