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ba1e2fe6 | 1 | /* Create new context. |
04277e02 | 2 | Copyright (C) 2002-2019 Free Software Foundation, Inc. |
ba1e2fe6 AJ |
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 | |
59ba27a6 | 17 | License along with the GNU C Library; if not, see |
5a82c748 | 18 | <https://www.gnu.org/licenses/>. */ |
ba1e2fe6 AJ |
19 | |
20 | #include <sysdep.h> | |
21 | #include <stdarg.h> | |
3cc4a097 | 22 | #include <stdint.h> |
ba1e2fe6 | 23 | #include <ucontext.h> |
25123a1c L |
24 | #if SHSTK_ENABLED |
25 | # include <pthread.h> | |
26 | # include <libc-pointer-arith.h> | |
27 | # include <sys/prctl.h> | |
28 | #endif | |
ba1e2fe6 AJ |
29 | |
30 | #include "ucontext_i.h" | |
31 | ||
32 | /* This implementation can handle any ARGC value but only | |
33 | normal integer parameters. | |
34 | makecontext sets up a stack and the registers for the | |
35 | user context. The stack looks like this: | |
36 | +-----------------------+ | |
37 | | next context | | |
38 | +-----------------------+ | |
39 | | parameter 7-n | | |
40 | +-----------------------+ | |
41 | | trampoline address | | |
42 | %rsp -> +-----------------------+ | |
43 | ||
44 | The registers are set up like this: | |
45 | %rdi,%rsi,%rdx,%rcx,%r8,%r9: parameter 1 to 6 | |
46 | %rbx : address of next context | |
47 | %rsp : stack pointer. | |
48 | */ | |
49 | ||
50 | /* XXX: This implementation currently only handles integer arguments. | |
51 | To handle long int and pointer arguments the va_arg arguments needs | |
52 | to be changed to long and also the stdlib/tst-setcontext.c file needs | |
53 | to be changed to pass long arguments to makecontext. */ | |
54 | ||
55 | ||
56 | void | |
57 | __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...) | |
58 | { | |
41e673c1 | 59 | extern void __start_context (void) attribute_hidden; |
25123a1c L |
60 | extern void __push___start_context (ucontext_t *) |
61 | attribute_hidden; | |
6b6cd74b L |
62 | greg_t *sp; |
63 | unsigned int idx_uc_link; | |
ba1e2fe6 AJ |
64 | va_list ap; |
65 | int i; | |
66 | ||
67 | /* Generate room on stack for parameter if needed and uc_link. */ | |
6b6cd74b L |
68 | sp = (greg_t *) ((uintptr_t) ucp->uc_stack.ss_sp |
69 | + ucp->uc_stack.ss_size); | |
c2df18a9 | 70 | sp -= (argc > 6 ? argc - 6 : 0) + 1; |
9f19140a | 71 | /* Align stack and make space for trampoline address. */ |
6b6cd74b | 72 | sp = (greg_t *) ((((uintptr_t) sp) & -16L) - 8); |
ba1e2fe6 | 73 | |
c2df18a9 | 74 | idx_uc_link = (argc > 6 ? argc - 6 : 0) + 1; |
ba1e2fe6 AJ |
75 | |
76 | /* Setup context ucp. */ | |
77 | /* Address to jump to. */ | |
6b6cd74b | 78 | ucp->uc_mcontext.gregs[REG_RIP] = (uintptr_t) func; |
ba1e2fe6 | 79 | /* Setup rbx.*/ |
6b6cd74b L |
80 | ucp->uc_mcontext.gregs[REG_RBX] = (uintptr_t) &sp[idx_uc_link]; |
81 | ucp->uc_mcontext.gregs[REG_RSP] = (uintptr_t) sp; | |
ba1e2fe6 AJ |
82 | |
83 | /* Setup stack. */ | |
25123a1c L |
84 | #if SHSTK_ENABLED |
85 | struct pthread *self = THREAD_SELF; | |
86 | unsigned int feature_1 = THREAD_GETMEM (self, header.feature_1); | |
87 | /* NB: We must check feature_1 before accessing __ssp since caller | |
88 | may be compiled against ucontext_t without __ssp. */ | |
89 | if ((feature_1 & X86_FEATURE_1_SHSTK) != 0) | |
90 | { | |
91 | /* Shadow stack is enabled. We need to allocate a new shadow | |
92 | stack. */ | |
93 | unsigned long ssp_size = (((uintptr_t) sp | |
94 | - (uintptr_t) ucp->uc_stack.ss_sp) | |
95 | >> STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT); | |
96 | /* Align shadow stack to 8 bytes. */ | |
97 | ssp_size = ALIGN_UP (ssp_size, 8); | |
98 | ||
99 | ucp->__ssp[1] = ssp_size; | |
100 | ucp->__ssp[2] = ssp_size; | |
101 | ||
102 | /* Call __push___start_context to allocate a new shadow stack, | |
103 | push __start_context onto the new stack as well as the new | |
104 | shadow stack. NB: After __push___start_context returns, | |
105 | ucp->__ssp[0]: The new shadow stack pointer. | |
106 | ucp->__ssp[1]: The base address of the new shadow stack. | |
107 | ucp->__ssp[2]: The size of the new shadow stack. | |
108 | */ | |
109 | __push___start_context (ucp); | |
110 | } | |
111 | else | |
112 | #endif | |
113 | sp[0] = (uintptr_t) &__start_context; | |
6b6cd74b | 114 | sp[idx_uc_link] = (uintptr_t) ucp->uc_link; |
ba1e2fe6 AJ |
115 | |
116 | va_start (ap, argc); | |
6c30d38f UD |
117 | /* Handle arguments. |
118 | ||
119 | The standard says the parameters must all be int values. This is | |
120 | an historic accident and would be done differently today. For | |
121 | x86-64 all integer values are passed as 64-bit values and | |
122 | therefore extending the API to copy 64-bit values instead of | |
123 | 32-bit ints makes sense. It does not break existing | |
124 | functionality and it does not violate the standard which says | |
125 | that passing non-int values means undefined behavior. */ | |
ba1e2fe6 AJ |
126 | for (i = 0; i < argc; ++i) |
127 | switch (i) | |
128 | { | |
129 | case 0: | |
6b6cd74b | 130 | ucp->uc_mcontext.gregs[REG_RDI] = va_arg (ap, greg_t); |
ba1e2fe6 AJ |
131 | break; |
132 | case 1: | |
6b6cd74b | 133 | ucp->uc_mcontext.gregs[REG_RSI] = va_arg (ap, greg_t); |
ba1e2fe6 AJ |
134 | break; |
135 | case 2: | |
6b6cd74b | 136 | ucp->uc_mcontext.gregs[REG_RDX] = va_arg (ap, greg_t); |
ba1e2fe6 AJ |
137 | break; |
138 | case 3: | |
6b6cd74b | 139 | ucp->uc_mcontext.gregs[REG_RCX] = va_arg (ap, greg_t); |
ba1e2fe6 AJ |
140 | break; |
141 | case 4: | |
6b6cd74b | 142 | ucp->uc_mcontext.gregs[REG_R8] = va_arg (ap, greg_t); |
ba1e2fe6 AJ |
143 | break; |
144 | case 5: | |
6b6cd74b | 145 | ucp->uc_mcontext.gregs[REG_R9] = va_arg (ap, greg_t); |
ba1e2fe6 AJ |
146 | break; |
147 | default: | |
148 | /* Put value on stack. */ | |
6b6cd74b | 149 | sp[i - 5] = va_arg (ap, greg_t); |
ba1e2fe6 AJ |
150 | break; |
151 | } | |
152 | va_end (ap); | |
153 | ||
154 | } | |
155 | ||
156 | ||
1ab18a5b | 157 | weak_alias (__makecontext, makecontext) |