[thirdparty/glibc.git] / sysdeps / unix / sysv / linux / i386 / vfork.S

/* Copyright (C) 1999-2019 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Andreas Schwab <schwab@gnu.org>.

   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>
#define _ERRNO_H	1
#include <bits/errno.h>
#include <tcb-offsets.h>

#if SHSTK_ENABLED
/* The shadow stack prevents us from pushing the saved return PC onto
   the stack and returning normally.  Instead we pop the shadow stack
   and return directly.  This is the safest way to return and ensures
   any stack manipulations done by the vfork'd child doesn't cause the
   parent to terminate when CET is enabled.  */
# undef SYSCALL_ERROR_HANDLER
# ifdef PIC
#  define SYSCALL_ERROR_HANDLER				\
0:							\
  calll .L1;						\
.L1:							\
  popl %edx;						\
.L2:							\
  addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx;	\
  movl __libc_errno@gotntpoff(%edx), %edx;		\
  negl %eax;						\
  movl %eax, %gs:(%edx);				\
  orl $-1, %eax;					\
  jmp 1b;
# else
#  define SYSCALL_ERROR_HANDLER				\
0:							\
  movl __libc_errno@indntpoff, %edx;			\
  negl %eax;						\
  movl %eax, %gs:(%edx);				\
  orl $-1, %eax;					\
  jmp 1b;
# endif
# undef SYSCALL_ERROR_LABEL
# define SYSCALL_ERROR_LABEL 0f
#endif

/* Clone the calling process, but without copying the whole address space.
   The calling process is suspended until the new process exits or is
   replaced by a call to `execve'.  Return -1 for errors, 0 to the new process,
   and the process ID of the new process to the old process.  */

ENTRY (__vfork)

	/* Pop the return PC value into ECX.  */
	popl	%ecx
	cfi_adjust_cfa_offset (-4)
	cfi_register (%eip, %ecx)

	/* Stuff the syscall number in EAX and enter into the kernel.  */
	movl	$SYS_ify (vfork), %eax
	int	$0x80

#if !SHSTK_ENABLED
	/* Jump to the return PC.  Don't jump directly since this
	   disturbs the branch target cache.  Instead push the return
	   address back on the stack.  */
	pushl	%ecx
	cfi_adjust_cfa_offset (4)
#endif

	cmpl	$-4095, %eax
	/* Branch forward if it failed.  */
	jae	SYSCALL_ERROR_LABEL

#if SHSTK_ENABLED
1:
	/* Check if shadow stack is in use.  */
	xorl	%edx, %edx
	rdsspd	%edx
	testl	%edx, %edx
	/* Normal return if shadow stack isn't in use.  */
	je	L(no_shstk)

	/* Pop return address from shadow stack and jump back to caller
	   directly.  */
	movl	$1, %edx
	incsspd	%edx
	jmp	*%ecx

L(no_shstk):
	/* Jump to the return PC.  Don't jump directly since this
	   disturbs the branch target cache.  Instead push the return
	   address back on the stack.  */
	pushl	%ecx
	cfi_adjust_cfa_offset (4)
#endif

	ret

PSEUDO_END (__vfork)
libc_hidden_def (__vfork)

weak_alias (__vfork, vfork)
strong_alias (__vfork, __libc_vfork)
Commit	Line	Data
04277e02	1	/* Copyright (C) 1999-2019 Free Software Foundation, Inc.
53ad957e UD	2	This file is part of the GNU C Library.
	3	Contributed by Andreas Schwab <schwab@gnu.org>.
	4
	5	The GNU C Library is free software; you can redistribute it and/or
41bdb6e2 AJ	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.
53ad957e UD	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
41bdb6e2	13	Lesser General Public License for more details.
53ad957e	14
41bdb6e2	15	You should have received a copy of the GNU Lesser General Public
59ba27a6	16	License along with the GNU C Library; if not, see
5a82c748	17	<https://www.gnu.org/licenses/>. */
53ad957e UD	18
	19	#include <sysdep.h>
	20	#define _ERRNO_H 1
	21	#include <bits/errno.h>
e2787137 RM	22	#include <tcb-offsets.h>
e2787137 RM	23
3650e1d9 L	24	#if SHSTK_ENABLED
	25	/* The shadow stack prevents us from pushing the saved return PC onto
	26	the stack and returning normally. Instead we pop the shadow stack
	27	and return directly. This is the safest way to return and ensures
	28	any stack manipulations done by the vfork'd child doesn't cause the
	29	parent to terminate when CET is enabled. */
	30	# undef SYSCALL_ERROR_HANDLER
	31	# ifdef PIC
	32	# define SYSCALL_ERROR_HANDLER \
	33	0: \
	34	calll .L1; \
	35	.L1: \
	36	popl %edx; \
	37	.L2: \
	38	addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \
	39	movl __libc_errno@gotntpoff(%edx), %edx; \
	40	negl %eax; \
	41	movl %eax, %gs:(%edx); \
	42	orl $-1, %eax; \
	43	jmp 1b;
	44	# else
	45	# define SYSCALL_ERROR_HANDLER \
	46	0: \
	47	movl __libc_errno@indntpoff, %edx; \
	48	negl %eax; \
	49	movl %eax, %gs:(%edx); \
	50	orl $-1, %eax; \
	51	jmp 1b;
	52	# endif
	53	# undef SYSCALL_ERROR_LABEL
	54	# define SYSCALL_ERROR_LABEL 0f
	55	#endif
53ad957e UD	56
	57	/* Clone the calling process, but without copying the whole address space.
	58	The calling process is suspended until the new process exits or is
	59	replaced by a call to `execve'. Return -1 for errors, 0 to the new process,
	60	and the process ID of the new process to the old process. */
	61
	62	ENTRY (__vfork)
	63
53ad957e UD	64	/* Pop the return PC value into ECX. */
53ad957e UD	65	popl %ecx
fee732e5	66	cfi_adjust_cfa_offset (-4)
6c30d38f	67	cfi_register (%eip, %ecx)
53ad957e UD	68
	69	/* Stuff the syscall number in EAX and enter into the kernel. */
	70	movl $SYS_ify (vfork), %eax
	71	int $0x80
70829603	72
3650e1d9	73	#if !SHSTK_ENABLED
70829603 UD	74	/* Jump to the return PC. Don't jump directly since this
	75	disturbs the branch target cache. Instead push the return
	76	address back on the stack. */
	77	pushl %ecx
fee732e5	78	cfi_adjust_cfa_offset (4)
3650e1d9	79	#endif
70829603	80
53ad957e	81	cmpl $-4095, %eax
70829603	82	/* Branch forward if it failed. */
70829603	83	jae SYSCALL_ERROR_LABEL
53ad957e	84
3650e1d9 L	85	#if SHSTK_ENABLED
	86	1:
	87	/* Check if shadow stack is in use. */
	88	xorl %edx, %edx
	89	rdsspd %edx
	90	testl %edx, %edx
	91	/* Normal return if shadow stack isn't in use. */
	92	je L(no_shstk)
	93
	94	/* Pop return address from shadow stack and jump back to caller
	95	directly. */
	96	movl $1, %edx
	97	incsspd %edx
	98	jmp *%ecx
	99
	100	L(no_shstk):
	101	/* Jump to the return PC. Don't jump directly since this
	102	disturbs the branch target cache. Instead push the return
	103	address back on the stack. */
	104	pushl %ecx
	105	cfi_adjust_cfa_offset (4)
	106	#endif
	107
70829603	108	ret
53ad957e	109
53ad957e	110	PSEUDO_END (__vfork)
a4baf360	111	libc_hidden_def (__vfork)
53ad957e UD	112
53ad957e UD	113	weak_alias (__vfork, vfork)
e2787137	114	strong_alias (__vfork, __libc_vfork)