1/* Copyright (C) 2001-2020 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18#include <sysdep.h>
19#define _ERRNO_H 1
20#include <bits/errno.h>
21#include <tcb-offsets.h>
22
23#if SHSTK_ENABLED
24/* The shadow stack prevents us from pushing the saved return PC onto
25 the stack and returning normally. Instead we pop the shadow stack
26 and return directly. This is the safest way to return and ensures
27 any stack manipulations done by the vfork'd child doesn't cause the
28 parent to terminate when CET is enabled. */
29# undef SYSCALL_ERROR_HANDLER
30# define SYSCALL_ERROR_HANDLER \
310: \
32 SYSCALL_SET_ERRNO; \
33 or $-1, %RAX_LP; \
34 jmp 1b;
35# undef SYSCALL_ERROR_LABEL
36# define SYSCALL_ERROR_LABEL 0f
37#endif
38
39/* Clone the calling process, but without copying the whole address space.
40 The calling process is suspended until the new process exits or is
41 replaced by a call to `execve'. Return -1 for errors, 0 to the new process,
42 and the process ID of the new process to the old process. */
43
44ENTRY (__vfork)
45
46 /* Pop the return PC value into RDI. We need a register that
47 is preserved by the syscall and that we're allowed to destroy. */
48 popq %rdi
49 cfi_adjust_cfa_offset(-8)
50 cfi_register(%rip, %rdi)
51
52 /* Stuff the syscall number in RAX and enter into the kernel. */
53 movl $SYS_ify (vfork), %eax
54 syscall
55
56#if !SHSTK_ENABLED
57 /* Push back the return PC. */
58 pushq %rdi
59 cfi_adjust_cfa_offset(8)
60#endif
61
62 cmpl $-4095, %eax
63 jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */
64
65#if SHSTK_ENABLED
661:
67 /* Check if shadow stack is in use. */
68 xorl %esi, %esi
69 rdsspq %rsi
70 testq %rsi, %rsi
71 /* Normal return if shadow stack isn't in use. */
72 je L(no_shstk)
73
74 /* Pop return address from shadow stack and jump back to caller
75 directly. */
76 movl $1, %esi
77 incsspq %rsi
78 jmp *%rdi
79
80L(no_shstk):
81 /* Push back the return PC. */
82 pushq %rdi
83 cfi_adjust_cfa_offset(8)
84#endif
85
86 /* Normal return. */
87 ret
88
89PSEUDO_END (__vfork)
90libc_hidden_def (__vfork)
91
92weak_alias (__vfork, vfork)
93strong_alias (__vfork, __libc_vfork)
94