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
  31 #include <rseq/rseq.h>
  32
  33 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
  34
  35 __thread struct rseq __rseq_abi = {
  36         .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
  37 };
  38
  39 static __thread uint32_t __rseq_refcount;
  40
  41 static int sys_rseq(struct rseq *rseq_abi, uint32_t rseq_len,
  42                     int flags, uint32_t sig)
  43 {
  44         return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
  45 }
  46
  47 int rseq_available(void)
  48 {
  49         int rc;
  50
  51         rc = sys_rseq(NULL, 0, 0, 0);
  52         if (rc != -1)
  53                 abort();
  54         switch (errno) {
  55         case ENOSYS:
  56                 return 0;
  57         case EINVAL:
  58                 return 1;
  59         default:
  60                 abort();
  61         }
  62 }
  63
  64 static void signal_off_save(sigset_t *oldset)
  65 {
  66         sigset_t set;
  67         int ret;
  68
  69         sigfillset(&set);
  70         ret = pthread_sigmask(SIG_BLOCK, &set, oldset);
  71         if (ret)
  72                 abort();
  73 }
  74
  75 static void signal_restore(sigset_t oldset)
  76 {
  77         int ret;
  78
  79         ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
  80         if (ret)
  81                 abort();
  82 }
  83
  84 int rseq_register_current_thread(void)
  85 {
  86         int rc, ret = 0, cpu_id;
  87         sigset_t oldset;
  88
  89         signal_off_save(&oldset);
  90         cpu_id = rseq_current_cpu_raw();
  91         if (cpu_id == RSEQ_CPU_ID_REGISTRATION_FAILED) {
  92                 errno = EPERM;
  93                 ret = -1;
  94                 goto end;
  95         }
  96         /*
  97          * If cpu_id >= 0, rseq is already successfully registered either by
  98          * libc (__rseq_refcount == 0) or by another user library
  99          * (__rseq_refcount > 0) for this thread.
 100          */
 101         if (cpu_id >= 0) {
 102                 /* Treat libc's ownership as a successful registration. */
 103                 if (__rseq_refcount == 0)
 104                         goto end;
 105                 if (__rseq_refcount == UINT_MAX) {
 106                         errno = EOVERFLOW;
 107                         ret = -1;
 108                         goto end;
 109                 }
 110         } else {
 111                 assert(__rseq_refcount == 0);
 112                 rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
 113                 if (rc) {
 114                         assert(errno != EBUSY);
 115                         __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
 116                         ret = -1;
 117                         goto end;
 118                 }
 119                 assert(rseq_current_cpu_raw() >= 0);
 120         }
 121         __rseq_refcount++;
 122 end:
 123         signal_restore(oldset);
 124         return ret;
 125 }
 126
 127 int rseq_unregister_current_thread(void)
 128 {
 129         int rc, ret = 0, cpu_id;
 130         sigset_t oldset;
 131
 132         signal_off_save(&oldset);
 133         cpu_id = rseq_current_cpu_raw();
 134         /* cpu_id < 0 means rseq is either uninitialized or registration failed. */
 135         if (cpu_id < 0) {
 136                 errno = EPERM;
 137                 ret = -1;
 138                 goto end;
 139         }
 140         /*
 141          * If cpu_id >= 0, rseq is currently successfully registered either by
 142          * libc (__rseq_refcount == 0) or by another user library
 143          * (__rseq_refcount > 0) for this thread.
 144          *
 145          * Treat libc's ownership as a successful unregistration.
 146          */
 147         if (__rseq_refcount == 0) {
 148                 goto end;
 149         }
 150         if (__rseq_refcount == 1) {
 151                 rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
 152                               RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
 153                 if (rc) {
 154                         ret = -1;
 155                         goto end;
 156                 }
 157         }
 158         __rseq_refcount--;
 159 end:
 160         signal_restore(oldset);
 161         return ret;
 162 }
 163
 164 int32_t rseq_fallback_current_cpu(void)
 165 {
 166         int32_t cpu;
 167
 168         cpu = sched_getcpu();
 169         if (cpu < 0) {
 170                 perror("sched_getcpu()");
 171                 abort();
 172         }
 173         return cpu;
 174 }