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
30 #include "rseq.h"
31
32 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
33
34 __thread volatile struct rseq __rseq_abi = {
35 .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
36 };
37
38 /*
39 * Shared with other libraries. This library may take rseq ownership if it is
40 * still 0 when executing the library constructor. Set to 1 by library
41 * constructor when handling rseq. Set to 0 in destructor if handling rseq.
42 */
43 int __rseq_handled;
44
45 /* Whether this library have ownership of rseq registration. */
46 static int rseq_ownership;
47
48 static __thread volatile uint32_t __rseq_refcount;
49
signal_off_save(sigset_t * oldset)50 static void signal_off_save(sigset_t *oldset)
51 {
52 sigset_t set;
53 int ret;
54
55 sigfillset(&set);
56 ret = pthread_sigmask(SIG_BLOCK, &set, oldset);
57 if (ret)
58 abort();
59 }
60
signal_restore(sigset_t oldset)61 static void signal_restore(sigset_t oldset)
62 {
63 int ret;
64
65 ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
66 if (ret)
67 abort();
68 }
69
sys_rseq(volatile struct rseq * rseq_abi,uint32_t rseq_len,int flags,uint32_t sig)70 static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len,
71 int flags, uint32_t sig)
72 {
73 return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
74 }
75
rseq_register_current_thread(void)76 int rseq_register_current_thread(void)
77 {
78 int rc, ret = 0;
79 sigset_t oldset;
80
81 if (!rseq_ownership)
82 return 0;
83 signal_off_save(&oldset);
84 if (__rseq_refcount == UINT_MAX) {
85 ret = -1;
86 goto end;
87 }
88 if (__rseq_refcount++)
89 goto end;
90 rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
91 if (!rc) {
92 assert(rseq_current_cpu_raw() >= 0);
93 goto end;
94 }
95 if (errno != EBUSY)
96 __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
97 ret = -1;
98 __rseq_refcount--;
99 end:
100 signal_restore(oldset);
101 return ret;
102 }
103
rseq_unregister_current_thread(void)104 int rseq_unregister_current_thread(void)
105 {
106 int rc, ret = 0;
107 sigset_t oldset;
108
109 if (!rseq_ownership)
110 return 0;
111 signal_off_save(&oldset);
112 if (!__rseq_refcount) {
113 ret = -1;
114 goto end;
115 }
116 if (--__rseq_refcount)
117 goto end;
118 rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
119 RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
120 if (!rc)
121 goto end;
122 __rseq_refcount = 1;
123 ret = -1;
124 end:
125 signal_restore(oldset);
126 return ret;
127 }
128
rseq_fallback_current_cpu(void)129 int32_t rseq_fallback_current_cpu(void)
130 {
131 int32_t cpu;
132
133 cpu = sched_getcpu();
134 if (cpu < 0) {
135 perror("sched_getcpu()");
136 abort();
137 }
138 return cpu;
139 }
140
rseq_init(void)141 void __attribute__((constructor)) rseq_init(void)
142 {
143 /* Check whether rseq is handled by another library. */
144 if (__rseq_handled)
145 return;
146 __rseq_handled = 1;
147 rseq_ownership = 1;
148 }
149
rseq_fini(void)150 void __attribute__((destructor)) rseq_fini(void)
151 {
152 if (!rseq_ownership)
153 return;
154 __rseq_handled = 0;
155 rseq_ownership = 0;
156 }
157