1 // SPDX-License-Identifier: LGPL-2.1
2 /*
3 * rseq.c
4 *
5 * Copyright (C) 2016 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
6 *
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; only
10 * version 2.1 of the License.
11 *
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 */
17
18 #define _GNU_SOURCE
19 #include <errno.h>
20 #include <sched.h>
21 #include <stdio.h>
22 #include <stdlib.h>
23 #include <string.h>
24 #include <unistd.h>
25 #include <syscall.h>
26 #include <assert.h>
27 #include <signal.h>
28 #include <limits.h>
29 #include <dlfcn.h>
30 #include <stddef.h>
31
32 #include "../kselftest.h"
33 #include "rseq.h"
34
35 static const ptrdiff_t *libc_rseq_offset_p;
36 static const unsigned int *libc_rseq_size_p;
37 static const unsigned int *libc_rseq_flags_p;
38
39 /* Offset from the thread pointer to the rseq area. */
40 ptrdiff_t rseq_offset;
41
42 /* Size of the registered rseq area. 0 if the registration was
43 unsuccessful. */
44 unsigned int rseq_size = -1U;
45
46 /* Flags used during rseq registration. */
47 unsigned int rseq_flags;
48
49 static int rseq_ownership;
50
51 static
52 __thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"))) = {
53 .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
54 };
55
sys_rseq(struct rseq_abi * rseq_abi,uint32_t rseq_len,int flags,uint32_t sig)56 static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len,
57 int flags, uint32_t sig)
58 {
59 return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
60 }
61
rseq_available(void)62 int rseq_available(void)
63 {
64 int rc;
65
66 rc = sys_rseq(NULL, 0, 0, 0);
67 if (rc != -1)
68 abort();
69 switch (errno) {
70 case ENOSYS:
71 return 0;
72 case EINVAL:
73 return 1;
74 default:
75 abort();
76 }
77 }
78
rseq_register_current_thread(void)79 int rseq_register_current_thread(void)
80 {
81 int rc;
82
83 if (!rseq_ownership) {
84 /* Treat libc's ownership as a successful registration. */
85 return 0;
86 }
87 rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), 0, RSEQ_SIG);
88 if (rc)
89 return -1;
90 assert(rseq_current_cpu_raw() >= 0);
91 return 0;
92 }
93
rseq_unregister_current_thread(void)94 int rseq_unregister_current_thread(void)
95 {
96 int rc;
97
98 if (!rseq_ownership) {
99 /* Treat libc's ownership as a successful unregistration. */
100 return 0;
101 }
102 rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
103 if (rc)
104 return -1;
105 return 0;
106 }
107
108 static __attribute__((constructor))
rseq_init(void)109 void rseq_init(void)
110 {
111 libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset");
112 libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size");
113 libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags");
114 if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p &&
115 *libc_rseq_size_p != 0) {
116 /* rseq registration owned by glibc */
117 rseq_offset = *libc_rseq_offset_p;
118 rseq_size = *libc_rseq_size_p;
119 rseq_flags = *libc_rseq_flags_p;
120 return;
121 }
122 if (!rseq_available())
123 return;
124 rseq_ownership = 1;
125 rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
126 rseq_size = sizeof(struct rseq_abi);
127 rseq_flags = 0;
128 }
129
130 static __attribute__((destructor))
rseq_exit(void)131 void rseq_exit(void)
132 {
133 if (!rseq_ownership)
134 return;
135 rseq_offset = 0;
136 rseq_size = -1U;
137 rseq_ownership = 0;
138 }
139
rseq_fallback_current_cpu(void)140 int32_t rseq_fallback_current_cpu(void)
141 {
142 int32_t cpu;
143
144 cpu = sched_getcpu();
145 if (cpu < 0) {
146 perror("sched_getcpu()");
147 abort();
148 }
149 return cpu;
150 }
151