src/rseq.c

   1 // SPDX-License-Identifier: LGPL-2.1-only
   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 #ifndef _GNU_SOURCE
  18 #define _GNU_SOURCE
  19 #endif
  20 #include <errno.h>
  21 #include <sched.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include <syscall.h>
  27 #include <assert.h>
  28 #include <signal.h>
  29 #include <limits.h>
  30 #include <dlfcn.h>
  31
  32 #include <rseq/rseq.h>
  33
  34 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
  35
  36 static const int *libc_rseq_offset_p;
  37 static const unsigned int *libc_rseq_size_p;
  38 static const unsigned int *libc_rseq_flags_p;
  39
  40 /* Offset from the thread pointer to the rseq area.  */
  41 int rseq_offset;
  42
  43 /* Size of the registered rseq area.  0 if the registration was
  44    unsuccessful.  */
  45 unsigned int rseq_size = -1U;
  46
  47 /* Flags used during rseq registration.  */
  48 unsigned int rseq_flags;
  49
  50 static int rseq_ownership;
  51
  52 static
  53 __thread struct rseq __rseq_abi __attribute__((tls_model("initial-exec"))) = {
  54         .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
  55 };
  56
  57 static int sys_rseq(struct rseq *rseq_abi, uint32_t rseq_len,
  58                     int flags, uint32_t sig)
  59 {
  60         return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
  61 }
  62
  63 int rseq_available(void)
  64 {
  65         int rc;
  66
  67         rc = sys_rseq(NULL, 0, 0, 0);
  68         if (rc != -1)
  69                 abort();
  70         switch (errno) {
  71         case ENOSYS:
  72                 return 0;
  73         case EINVAL:
  74                 return 1;
  75         default:
  76                 abort();
  77         }
  78 }
  79
  80 int rseq_register_current_thread(void)
  81 {
  82         int rc;
  83
  84         if (!rseq_ownership) {
  85                 /* Treat libc's ownership as a successful registration. */
  86                 return 0;
  87         }
  88         rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
  89         if (rc)
  90                 return -1;
  91         assert(rseq_current_cpu_raw() >= 0);
  92         return 0;
  93 }
  94
  95 int rseq_unregister_current_thread(void)
  96 {
  97         int rc;
  98
  99         if (!rseq_ownership) {
 100                 /* Treat libc's ownership as a successful unregistration. */
 101                 return 0;
 102         }
 103         rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
 104         if (rc)
 105                 return -1;
 106         return 0;
 107 }
 108
 109 static __attribute__((constructor))
 110 void rseq_init(void)
 111 {
 112         libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset");
 113         libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size");
 114         libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags");
 115         if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p) {
 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);
 127         rseq_flags = 0;
 128 }
 129
 130 static __attribute__((destructor))
 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
 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 }