1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
|
/* Create new 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(__makecontext)
movl 4(%esp), %eax
/* Load the address of the function we are supposed to run. */
movl 8(%esp), %ecx
/* Compute the address of the stack. The information comes from
to us_stack element. */
movl oSS_SP(%eax), %edx
movl %ecx, oEIP(%eax)
addl oSS_SIZE(%eax), %edx
/* Remember the number of parameters for the exit handler since
it has to remove them. We store the number in the EBX register
which the function we will call must preserve. */
movl 12(%esp), %ecx
movl %ecx, oEBX(%eax)
/* Make room on the new stack for the parameters.
Room for the arguments, return address (== L(exitcode)) and
oLINK pointer is needed. One of the pointer sizes is subtracted
after aligning the stack. */
negl %ecx
leal -4(%edx,%ecx,4), %edx
negl %ecx
/* Align the stack. */
andl $0xfffffff0, %edx
subl $4, %edx
/* Store the future stack pointer. */
movl %edx, oESP(%eax)
/* Put the next context on the new stack (from the uc_link
element). */
movl oLINK(%eax), %eax
movl %eax, 4(%edx,%ecx,4)
/* Copy all the parameters. */
jecxz 2f
1: movl 12(%esp,%ecx,4), %eax
movl %eax, (%edx,%ecx,4)
decl %ecx
jnz 1b
2:
#if SHSTK_ENABLED
/* Check if Shadow Stack is enabled. */
testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
jz L(skip_ssp)
/* Reload the pointer to ucontext. */
movl 4(%esp), %eax
/* Shadow stack is enabled. We need to allocate a new shadow
stack. */
subl oSS_SP(%eax), %edx
shrl $STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT, %edx
/* Align shadow stack size to 8 bytes. */
addl $7, %edx
andl $-8, %edx
/* Store shadow stack size in __ssp[2]. */
movl %edx, (oSSP + 8)(%eax)
/* Save ESI in the second scratch register slot. */
movl %esi, oSCRATCH2(%eax)
/* Save EDI in the third scratch register slot. */
movl %edi, oSCRATCH3(%eax)
/* Save the pointer to ucontext. */
movl %eax, %edi
/* Get the original shadow stack pointer. */
rdsspd %esi
/* Align the saved original shadow stack pointer to the next
8 byte aligned boundary. */
andl $-8, %esi
/* Load the top of the new stack into EDX. */
movl oESP(%eax), %edx
/* We need to terminate the FDE here because the unwinder looks
at ra-1 for unwind information. */
cfi_endproc
/* Swap the original stack pointer with the top of the new
stack. */
xchgl %esp, %edx
/* Add 4 bytes since CALL will push the 4-byte return address
onto stack. */
addl $4, %esp
/* Allocate the new shadow stack. Save EBX in the first scratch
register slot. */
movl %ebx, oSCRATCH1(%eax)
/* CET syscall takes 64-bit sizes. */
subl $16, %esp
movl (oSSP + 8)(%eax), %ecx
movl %ecx, (%esp)
movl $0, 4(%esp)
movl %ecx, 8(%esp)
movl $0, 12(%esp)
movl %esp, %ecx
movl $ARCH_CET_ALLOC_SHSTK, %ebx
movl $__NR_arch_prctl, %eax
ENTER_KERNEL
testl %eax, %eax
jne L(hlt) /* This should never happen. */
/* Copy the base address of the new shadow stack to __ssp[1]. */
movl (%esp), %eax
movl %eax, (oSSP + 4)(%edi)
addl $16, %esp
/* Restore EBX from the first scratch register slot. */
movl oSCRATCH1(%edi), %ebx
/* Get the size of the new shadow stack. */
movl (oSSP + 8)(%edi), %ecx
/* Use the restore stoken to restore the new shadow stack. */
rstorssp -8(%eax, %ecx)
/* Save the restore token at the next 8 byte aligned boundary
on the original shadow stack. */
saveprevssp
/* Push the address of "jmp exitcode" onto the new stack as
well as the new shadow stack. */
call 1f
jmp L(exitcode)
1:
/* Get the new shadow stack pointer. */
rdsspd %eax
/* Use the restore stoken to restore the original shadow stack. */
rstorssp -8(%esi)
/* Save the restore token on the new shadow stack. */
saveprevssp
/* Store the new shadow stack pointer in __ssp[0]. */
movl %eax, oSSP(%edi)
/* Restore the original stack. */
mov %edx, %esp
cfi_startproc
/* Restore ESI from the second scratch register slot. */
movl oSCRATCH2(%edi), %esi
/* Restore EDI from the third scratch register slot. */
movl oSCRATCH3(%edi), %edi
ret
L(skip_ssp):
#endif
/* If the function we call returns we must continue with the
context which is given in the uc_link element. To do this
set the return address for the function the user provides
to a little bit of helper code which does the magic (see
below). */
#ifdef PIC
call 1f
cfi_adjust_cfa_offset (4)
1: popl %ecx
cfi_adjust_cfa_offset (-4)
addl $L(exitcode)-1b, %ecx
movl %ecx, (%edx)
#else
movl $L(exitcode), (%edx)
#endif
/* We need to terminate the FDE here instead of after ret because
the unwinder looks at ra-1 for unwind information. */
cfi_endproc
/* 'makecontext' returns no value. */
ret
/* This is the helper code which gets called if a function which
is registered with 'makecontext' returns. In this case we
have to install the context listed in the uc_link element of
the context 'makecontext' manipulated at the time of the
'makecontext' call. If the pointer is NULL the process must
terminate. */
L(exitcode):
/* This removes the parameters passed to the function given to
'makecontext' from the stack. EBX contains the number of
parameters (see above). */
leal (%esp,%ebx,4), %esp
cmpl $0, (%esp) /* Check the next context. */
je 2f /* If it is zero exit. */
call HIDDEN_JUMPTARGET(__setcontext)
/* If this returns (which can happen if the syscall fails) we'll
exit the program with the return error value (-1). */
jmp L(call_exit)
2:
/* Exit with status 0. */
xorl %eax, %eax
L(call_exit):
/* Align the stack and pass the exit code (from %eax). */
andl $0xfffffff0, %esp
subl $12, %esp
pushl %eax
call HIDDEN_JUMPTARGET(exit)
/* The 'exit' call should never return. In case it does cause
the process to terminate. */
L(hlt):
hlt
cfi_startproc
END(__makecontext)
weak_alias (__makecontext, makecontext)
|
