1/* Install given context.
2 Copyright (C) 2002-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
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.
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
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <sysdep.h>
20#include <asm/prctl.h>
21
22#include "ucontext_i.h"
23
24
25/* int __setcontext (const ucontext_t *ucp)
26
27 Restores the machine context in UCP and thereby resumes execution
28 in that context.
29
30 This implementation is intended to be used for *synchronous* context
31 switches only. Therefore, it does not have to restore anything
32 other than the PRESERVED state. */
33
34ENTRY(__setcontext)
35 /* Save argument since syscall will destroy it. */
36 pushq %rdi
37 cfi_adjust_cfa_offset(8)
38
39 /* Set the signal mask with
40 rt_sigprocmask (SIG_SETMASK, mask, NULL, _NSIG/8). */
41 leaq oSIGMASK(%rdi), %rsi
42 xorl %edx, %edx
43 movl $SIG_SETMASK, %edi
44 movl $_NSIG8,%r10d
45 movl $__NR_rt_sigprocmask, %eax
46 syscall
47 /* Pop the pointer into RDX. The choice is arbitrary, but
48 leaving RDI and RSI available for use later can avoid
49 shuffling values. */
50 popq %rdx
51 cfi_adjust_cfa_offset(-8)
52 cmpq $-4095, %rax /* Check %rax for error. */
53 jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
54
55 /* Restore the floating-point context. Not the registers, only the
56 rest. */
57 movq oFPREGS(%rdx), %rcx
58 fldenv (%rcx)
59 ldmxcsr oMXCSR(%rdx)
60
61
62 /* Load the new stack pointer, the preserved registers and
63 registers used for passing args. */
64 cfi_def_cfa(%rdx, 0)
65 cfi_offset(%rbx,oRBX)
66 cfi_offset(%rbp,oRBP)
67 cfi_offset(%r12,oR12)
68 cfi_offset(%r13,oR13)
69 cfi_offset(%r14,oR14)
70 cfi_offset(%r15,oR15)
71 cfi_offset(%rsp,oRSP)
72 cfi_offset(%rip,oRIP)
73
74 movq oRSP(%rdx), %rsp
75 movq oRBX(%rdx), %rbx
76 movq oRBP(%rdx), %rbp
77 movq oR12(%rdx), %r12
78 movq oR13(%rdx), %r13
79 movq oR14(%rdx), %r14
80 movq oR15(%rdx), %r15
81
82#if SHSTK_ENABLED
83 /* Check if shadow stack is enabled. */
84 testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
85 jz L(no_shstk)
86
87 /* If the base of the target shadow stack is the same as the
88 base of the current shadow stack, we unwind the shadow
89 stack. Otherwise it is a stack switch and we look for a
90 restore token. */
91 movq oSSP(%rdx), %rsi
92 movq %rsi, %rdi
93
94 /* Get the base of the target shadow stack. */
95 movq (oSSP + 8)(%rdx), %rcx
96 cmpq %fs:SSP_BASE_OFFSET, %rcx
97 je L(unwind_shadow_stack)
98
99L(find_restore_token_loop):
100 /* Look for a restore token. */
101 movq -8(%rsi), %rax
102 andq $-8, %rax
103 cmpq %rsi, %rax
104 je L(restore_shadow_stack)
105
106 /* Try the next slot. */
107 subq $8, %rsi
108 jmp L(find_restore_token_loop)
109
110L(restore_shadow_stack):
111 /* Pop return address from the shadow stack since setcontext
112 will not return. */
113 movq $1, %rax
114 incsspq %rax
115
116 /* Use the restore stoken to restore the target shadow stack. */
117 rstorssp -8(%rsi)
118
119 /* Save the restore token on the old shadow stack. NB: This
120 restore token may be checked by setcontext or swapcontext
121 later. */
122 saveprevssp
123
124 /* Record the new shadow stack base that was switched to. */
125 movq (oSSP + 8)(%rdx), %rax
126 movq %rax, %fs:SSP_BASE_OFFSET
127
128L(unwind_shadow_stack):
129 rdsspq %rcx
130 subq %rdi, %rcx
131 je L(skip_unwind_shadow_stack)
132 negq %rcx
133 shrq $3, %rcx
134 movl $255, %esi
135L(loop):
136 cmpq %rsi, %rcx
137 cmovb %rcx, %rsi
138 incsspq %rsi
139 subq %rsi, %rcx
140 ja L(loop)
141
142L(skip_unwind_shadow_stack):
143 movq oRSI(%rdx), %rsi
144 movq oRDI(%rdx), %rdi
145 movq oRCX(%rdx), %rcx
146 movq oR8(%rdx), %r8
147 movq oR9(%rdx), %r9
148
149 /* Get the return address set with getcontext. */
150 movq oRIP(%rdx), %r10
151
152 /* Setup finally %rdx. */
153 movq oRDX(%rdx), %rdx
154
155 /* Check if return address is valid for the case when setcontext
156 is invoked from __start_context with linked context. */
157 rdsspq %rax
158 cmpq (%rax), %r10
159 /* Clear RAX to indicate success. NB: Don't use xorl to keep
160 EFLAGS for jne. */
161 movl $0, %eax
162 jne L(jmp)
163 /* Return to the new context if return address valid. */
164 pushq %r10
165 ret
166
167L(jmp):
168 /* Jump to the new context directly. */
169 jmp *%r10
170
171L(no_shstk):
172#endif
173 /* The following ret should return to the address set with
174 getcontext. Therefore push the address on the stack. */
175 movq oRIP(%rdx), %rcx
176 pushq %rcx
177
178 movq oRSI(%rdx), %rsi
179 movq oRDI(%rdx), %rdi
180 movq oRCX(%rdx), %rcx
181 movq oR8(%rdx), %r8
182 movq oR9(%rdx), %r9
183
184 /* Setup finally %rdx. */
185 movq oRDX(%rdx), %rdx
186
187 /* End FDE here, we fall into another context. */
188 cfi_endproc
189 cfi_startproc
190
191 /* Clear rax to indicate success. */
192 xorl %eax, %eax
193 ret
194PSEUDO_END(__setcontext)
195
196weak_alias (__setcontext, setcontext)
197

source code of glibc/sysdeps/unix/sysv/linux/x86_64/setcontext.S