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