1/* Install given context.
2 Copyright (C) 2002-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Andreas Jaeger <aj@suse.de>, 2002.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#include <sysdep.h>
21#include <asm/prctl.h>
22
23#include "ucontext_i.h"
24
25
26/* int __setcontext (const ucontext_t *ucp)
27
28 Restores the machine context in UCP and thereby resumes execution
29 in that context.
30
31 This implementation is intended to be used for *synchronous* context
32 switches only. Therefore, it does not have to restore anything
33 other than the PRESERVED state. */
34
35ENTRY(__setcontext)
36 /* Save argument since syscall will destroy it. */
37 pushq %rdi
38 cfi_adjust_cfa_offset(8)
39
40 /* Set the signal mask with
41 rt_sigprocmask (SIG_SETMASK, mask, NULL, _NSIG/8). */
42 leaq oSIGMASK(%rdi), %rsi
43 xorl %edx, %edx
44 movl $SIG_SETMASK, %edi
45 movl $_NSIG8,%r10d
46 movl $__NR_rt_sigprocmask, %eax
47 syscall
48 /* Pop the pointer into RDX. The choice is arbitrary, but
49 leaving RDI and RSI available for use later can avoid
50 shuffling values. */
51 popq %rdx
52 cfi_adjust_cfa_offset(-8)
53 cmpq $-4095, %rax /* Check %rax for error. */
54 jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
55
56 /* Restore the floating-point context. Not the registers, only the
57 rest. */
58 movq oFPREGS(%rdx), %rcx
59 fldenv (%rcx)
60 ldmxcsr oMXCSR(%rdx)
61
62
63 /* Load the new stack pointer, the preserved registers and
64 registers used for passing args. */
65 cfi_def_cfa(%rdx, 0)
66 cfi_offset(%rbx,oRBX)
67 cfi_offset(%rbp,oRBP)
68 cfi_offset(%r12,oR12)
69 cfi_offset(%r13,oR13)
70 cfi_offset(%r14,oR14)
71 cfi_offset(%r15,oR15)
72 cfi_offset(%rsp,oRSP)
73 cfi_offset(%rip,oRIP)
74
75 movq oRSP(%rdx), %rsp
76 movq oRBX(%rdx), %rbx
77 movq oRBP(%rdx), %rbp
78 movq oR12(%rdx), %r12
79 movq oR13(%rdx), %r13
80 movq oR14(%rdx), %r14
81 movq oR15(%rdx), %r15
82
83#if SHSTK_ENABLED
84 /* Check if shadow stack is enabled. */
85 testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
86 jz L(no_shstk)
87
88 /* If the base of the target shadow stack is the same as the
89 base of the current shadow stack, we unwind the shadow
90 stack. Otherwise it is a stack switch and we look for a
91 restore token. */
92 movq oSSP(%rdx), %rsi
93 movq %rsi, %rdi
94
95 /* Get the base of the target shadow stack. */
96 movq (oSSP + 8)(%rdx), %rcx
97 cmpq %fs:SSP_BASE_OFFSET, %rcx
98 je L(unwind_shadow_stack)
99
100L(find_restore_token_loop):
101 /* Look for a restore token. */
102 movq -8(%rsi), %rax
103 andq $-8, %rax
104 cmpq %rsi, %rax
105 je L(restore_shadow_stack)
106
107 /* Try the next slot. */
108 subq $8, %rsi
109 jmp L(find_restore_token_loop)
110
111L(restore_shadow_stack):
112 /* Pop return address from the shadow stack since setcontext
113 will not return. */
114 movq $1, %rax
115 incsspq %rax
116
117 /* Use the restore stoken to restore the target shadow stack. */
118 rstorssp -8(%rsi)
119
120 /* Save the restore token on the old shadow stack. NB: This
121 restore token may be checked by setcontext or swapcontext
122 later. */
123 saveprevssp
124
125 /* Record the new shadow stack base that was switched to. */
126 movq (oSSP + 8)(%rdx), %rax
127 movq %rax, %fs:SSP_BASE_OFFSET
128
129L(unwind_shadow_stack):
130 rdsspq %rcx
131 subq %rdi, %rcx
132 je L(skip_unwind_shadow_stack)
133 negq %rcx
134 shrq $3, %rcx
135 movl $255, %esi
136L(loop):
137 cmpq %rsi, %rcx
138 cmovb %rcx, %rsi
139 incsspq %rsi
140 subq %rsi, %rcx
141 ja L(loop)
142
143L(skip_unwind_shadow_stack):
144 movq oRSI(%rdx), %rsi
145 movq oRDI(%rdx), %rdi
146 movq oRCX(%rdx), %rcx
147 movq oR8(%rdx), %r8
148 movq oR9(%rdx), %r9
149
150 /* Get the return address set with getcontext. */
151 movq oRIP(%rdx), %r10
152
153 /* Setup finally %rdx. */
154 movq oRDX(%rdx), %rdx
155
156 /* Check if return address is valid for the case when setcontext
157 is invoked from __start_context with linked context. */
158 rdsspq %rax
159 cmpq (%rax), %r10
160 /* Clear RAX to indicate success. NB: Don't use xorl to keep
161 EFLAGS for jne. */
162 movl $0, %eax
163 jne L(jmp)
164 /* Return to the new context if return address valid. */
165 pushq %r10
166 ret
167
168L(jmp):
169 /* Jump to the new context directly. */
170 jmp *%r10
171
172L(no_shstk):
173#endif
174 /* The following ret should return to the address set with
175 getcontext. Therefore push the address on the stack. */
176 movq oRIP(%rdx), %rcx
177 pushq %rcx
178
179 movq oRSI(%rdx), %rsi
180 movq oRDI(%rdx), %rdi
181 movq oRCX(%rdx), %rcx
182 movq oR8(%rdx), %r8
183 movq oR9(%rdx), %r9
184
185 /* Setup finally %rdx. */
186 movq oRDX(%rdx), %rdx
187
188 /* End FDE here, we fall into another context. */
189 cfi_endproc
190 cfi_startproc
191
192 /* Clear rax to indicate success. */
193 xorl %eax, %eax
194 ret
195PSEUDO_END(__setcontext)
196
197weak_alias (__setcontext, setcontext)
198