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
|
/* Save current context and install the given one.
Copyright (C) 2002-2019 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Andreas Jaeger <aj@suse.de>, 2002.
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"
/* int __swapcontext (ucontext_t *oucp, const ucontext_t *ucp);
Saves the machine context in oucp such that when it is activated,
it appears as if __swapcontextt() returned again, restores the
machine context in ucp and thereby resumes execution in that
context.
This implementation is intended to be used for *synchronous* context
switches only. Therefore, it does not have to save anything
other than the PRESERVED state. */
ENTRY(__swapcontext)
/* Save the preserved registers, the registers used for passing args,
and the return address. */
movq %rbx, oRBX(%rdi)
movq %rbp, oRBP(%rdi)
movq %r12, oR12(%rdi)
movq %r13, oR13(%rdi)
movq %r14, oR14(%rdi)
movq %r15, oR15(%rdi)
movq %rdi, oRDI(%rdi)
movq %rsi, oRSI(%rdi)
movq %rdx, oRDX(%rdi)
movq %rcx, oRCX(%rdi)
movq %r8, oR8(%rdi)
movq %r9, oR9(%rdi)
movq (%rsp), %rcx
movq %rcx, oRIP(%rdi)
leaq 8(%rsp), %rcx /* Exclude the return address. */
movq %rcx, oRSP(%rdi)
/* We have separate floating-point register content memory on the
stack. We use the __fpregs_mem block in the context. Set the
links up correctly. */
leaq oFPREGSMEM(%rdi), %rcx
movq %rcx, oFPREGS(%rdi)
/* Save the floating-point environment. */
fnstenv (%rcx)
stmxcsr oMXCSR(%rdi)
/* The syscall destroys some registers, save them. */
movq %rsi, %r12
movq %rdi, %r9
/* Save the current signal mask and install the new one with
rt_sigprocmask (SIG_BLOCK, newset, oldset,_NSIG/8). */
leaq oSIGMASK(%rdi), %rdx
leaq oSIGMASK(%rsi), %rsi
movl $SIG_SETMASK, %edi
movl $_NSIG8,%r10d
movl $__NR_rt_sigprocmask, %eax
syscall
cmpq $-4095, %rax /* Check %rax for error. */
jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
/* Restore destroyed register into RDX. The choice is arbitrary,
but leaving RDI and RSI available for use later can avoid
shuffling values. */
movq %r12, %rdx
/* Restore the floating-point context. Not the registers, only the
rest. */
movq oFPREGS(%rdx), %rcx
fldenv (%rcx)
ldmxcsr oMXCSR(%rdx)
/* Load the new stack pointer and the preserved registers. */
movq oRSP(%rdx), %rsp
movq oRBX(%rdx), %rbx
movq oRBP(%rdx), %rbp
movq oR12(%rdx), %r12
movq oR13(%rdx), %r13
movq oR14(%rdx), %r14
movq oR15(%rdx), %r15
#if SHSTK_ENABLED
/* Check if shadow stack is enabled. */
testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
jz L(no_shstk)
xorl %eax, %eax
cmpq %fs:SSP_BASE_OFFSET, %rax
jnz L(shadow_stack_bound_recorded)
/* Get the base address and size of the default shadow stack
which must be the current shadow stack since nothing has
been recorded yet. */
sub $24, %RSP_LP
mov %RSP_LP, %RSI_LP
movl $ARCH_CET_STATUS, %edi
movl $__NR_arch_prctl, %eax
syscall
testq %rax, %rax
jz L(continue_no_err)
/* This should never happen. */
hlt
L(continue_no_err):
/* Record the base of the current shadow stack. */
movq 8(%rsp), %rax
movq %rax, %fs:SSP_BASE_OFFSET
add $24, %RSP_LP
L(shadow_stack_bound_recorded):
/* If we unwind the stack, we can't undo stack unwinding. Just
save the target shadow stack pointer as the current shadow
stack pointer. */
movq oSSP(%rdx), %rcx
movq %rcx, oSSP(%r9)
/* Save the base of the current shadow stack. */
movq %fs:SSP_BASE_OFFSET, %rax
movq %rax, (oSSP + 8)(%r9)
/* 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. */
movq oSSP(%rdx), %rsi
movq %rsi, %rdi
/* Get the base of the target shadow stack. */
movq (oSSP + 8)(%rdx), %rcx
cmpq %fs:SSP_BASE_OFFSET, %rcx
je L(unwind_shadow_stack)
L(find_restore_token_loop):
/* Look for a restore token. */
movq -8(%rsi), %rax
andq $-8, %rax
cmpq %rsi, %rax
je L(restore_shadow_stack)
/* Try the next slot. */
subq $8, %rsi
jmp L(find_restore_token_loop)
L(restore_shadow_stack):
/* The target shadow stack will be restored. Save the current
shadow stack pointer. */
rdsspq %rcx
movq %rcx, oSSP(%r9)
/* Restore the target shadow stack. */
rstorssp -8(%rsi)
/* 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. */
movq (oSSP + 8)(%rdx), %rax
movq %rax, %fs:SSP_BASE_OFFSET
L(unwind_shadow_stack):
rdsspq %rcx
subq %rdi, %rcx
je L(skip_unwind_shadow_stack)
negq %rcx
shrq $3, %rcx
movl $255, %esi
L(loop):
cmpq %rsi, %rcx
cmovb %rcx, %rsi
incsspq %rsi
subq %rsi, %rcx
ja L(loop)
L(skip_unwind_shadow_stack):
/* Setup registers used for passing args. */
movq oRDI(%rdx), %rdi
movq oRSI(%rdx), %rsi
movq oRCX(%rdx), %rcx
movq oR8(%rdx), %r8
movq oR9(%rdx), %r9
/* Get the return address set with getcontext. */
movq oRIP(%rdx), %r10
/* Setup finally %rdx. */
movq oRDX(%rdx), %rdx
/* Check if return address is valid for the case when setcontext
is invoked from __start_context with linked context. */
rdsspq %rax
cmpq (%rax), %r10
/* Clear rax 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. */
pushq %r10
ret
L(jmp):
/* Jump to the new context directly. */
jmp *%r10
L(no_shstk):
#endif
/* The following ret should return to the address set with
getcontext. Therefore push the address on the stack. */
movq oRIP(%rdx), %rcx
pushq %rcx
/* Setup registers used for passing args. */
movq oRDI(%rdx), %rdi
movq oRSI(%rdx), %rsi
movq oRCX(%rdx), %rcx
movq oR8(%rdx), %r8
movq oR9(%rdx), %r9
/* Setup finally %rdx. */
movq oRDX(%rdx), %rdx
/* Clear rax to indicate success. */
xorl %eax, %eax
ret
PSEUDO_END(__swapcontext)
weak_alias (__swapcontext, swapcontext)
|
