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 
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 
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 
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 
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))
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 		/* rseq registration owned by glibc */
116 		rseq_offset = *libc_rseq_offset_p;
117 		rseq_size = *libc_rseq_size_p;
118 		rseq_flags = *libc_rseq_flags_p;
119 		return;
120 	}
121 	if (!rseq_available())
122 		return;
123 	rseq_ownership = 1;
124 	rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
125 	rseq_size = sizeof(struct rseq_abi);
126 	rseq_flags = 0;
127 }
128 
129 static __attribute__((destructor))
130 void rseq_exit(void)
131 {
132 	if (!rseq_ownership)
133 		return;
134 	rseq_offset = 0;
135 	rseq_size = -1U;
136 	rseq_ownership = 0;
137 }
138 
139 int32_t rseq_fallback_current_cpu(void)
140 {
141 	int32_t cpu;
142 
143 	cpu = sched_getcpu();
144 	if (cpu < 0) {
145 		perror("sched_getcpu()");
146 		abort();
147 	}
148 	return cpu;
149 }
150