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 
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 
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 
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 
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 
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 
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 
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 
150 void __attribute__((destructor)) rseq_fini(void)
151 {
152 	if (!rseq_ownership)
153 		return;
154 	__rseq_handled = 0;
155 	rseq_ownership = 0;
156 }
157