1/* Copyright (C) 2002-2022 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
20#if SHSTK_ENABLED
21# include <asm/prctl.h>
22# include "ucontext_i.h"
23
24/* Use CALL to push __start_context onto the new stack as well as the new
25   shadow stack.  RDI points to ucontext:
26   Incoming:
27     __ssp[0]: The original caller's shadow stack pointer.
28     __ssp[1]: The size of the new shadow stack.
29     __ssp[2]: The size of the new shadow stack.
30   Outgoing:
31     __ssp[0]: The new shadow stack pointer.
32     __ssp[1]: The base address of the new shadow stack.
33     __ssp[2]: The size of the new shadow stack.
34 */
35
36ENTRY(__push___start_context)
37	/* Save the pointer to ucontext.  */
38	movq	%rdi, %r9
39	/* Get the original shadow stack pointer.  */
40	rdsspq	%r8
41	/* Save the original stack pointer.  */
42	movq	%rsp, %rdx
43	/* Load the top of the new stack into RSI.  */
44	movq 	oRSP(%rdi), %rsi
45	/* Add 8 bytes to RSI since CALL will push the 8-byte return
46	   address onto stack.  */
47	leaq	8(%rsi), %rsp
48	/* Allocate the new shadow stack.  The size of the new shadow
49	   stack is passed in __ssp[1].  */
50	lea	(oSSP + 8)(%rdi), %RSI_LP
51	movl	$ARCH_CET_ALLOC_SHSTK, %edi
52	movl	$__NR_arch_prctl, %eax
53	/* The new shadow stack base is returned in __ssp[1].  */
54	syscall
55	testq	%rax, %rax
56	jne	L(hlt)		/* This should never happen.  */
57
58	/* Get the size of the new shadow stack.  */
59	movq	8(%rsi), %rdi
60
61	/* Get the base address of the new shadow stack.  */
62	movq	(%rsi), %rsi
63
64	/* Use the restore stoken to restore the new shadow stack.  */
65	rstorssp -8(%rsi, %rdi)
66
67	/* Save the restore token on the original shadow stack.  */
68	saveprevssp
69
70	/* Push the address of "jmp __start_context" onto the new stack
71	   as well as the new shadow stack.  */
72	call	1f
73	jmp	__start_context
741:
75
76	/* Get the new shadow stack pointer.  */
77	rdsspq	%rdi
78
79	/* Use the restore stoken to restore the original shadow stack.  */
80	rstorssp -8(%r8)
81
82	/* Save the restore token on the new shadow stack.  */
83	saveprevssp
84
85	/* Store the new shadow stack pointer in __ssp[0].  */
86	movq	%rdi, oSSP(%r9)
87
88	/* Restore the original stack.  */
89	mov	%rdx, %rsp
90	ret
91END(__push___start_context)
92#endif
93
94/* This is the helper code which gets called if a function which is
95   registered with 'makecontext' returns.  In this case we have to
96   install the context listed in the uc_link element of the context
97   'makecontext' manipulated at the time of the 'makecontext' call.
98   If the pointer is NULL the process must terminate.  */
99
100
101ENTRY(__start_context)
102	/* This removes the parameters passed to the function given to
103	   'makecontext' from the stack.  RBX contains the address
104	   on the stack pointer for the next context.  */
105	movq	%rbx, %rsp
106
107	/* Don't use pop here so that stack is aligned to 16 bytes.  */
108	movq	(%rsp), %rdi		/* This is the next context.  */
109	testq	%rdi, %rdi
110	je	2f			/* If it is zero exit.  */
111
112	call	__setcontext
113	/* If this returns (which can happen if the syscall fails) we'll
114	   exit the program with the return error value (-1).  */
115	movq	%rax,%rdi
116
1172:
118	call	HIDDEN_JUMPTARGET(exit)
119	/* The 'exit' call should never return.  In case it does cause
120	   the process to terminate.  */
121L(hlt):
122	hlt
123END(__start_context)
124