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#include <sys/auxv.h> 32#include <linux/auxvec.h> 33 34#include <linux/compiler.h> 35 36#include "../kselftest.h" 37#include "rseq.h" 38 39/* 40 * Define weak versions to play nice with binaries that are statically linked 41 * against a libc that doesn't support registering its own rseq. 42 */ 43__weak ptrdiff_t __rseq_offset; 44__weak unsigned int __rseq_size; 45__weak unsigned int __rseq_flags; 46 47static const ptrdiff_t *libc_rseq_offset_p = &__rseq_offset; 48static const unsigned int *libc_rseq_size_p = &__rseq_size; 49static const unsigned int *libc_rseq_flags_p = &__rseq_flags; 50 51/* Offset from the thread pointer to the rseq area. */ 52ptrdiff_t rseq_offset; 53 54/* 55 * Size of the registered rseq area. 0 if the registration was 56 * unsuccessful. 57 */ 58unsigned int rseq_size = -1U; 59 60/* Flags used during rseq registration. */ 61unsigned int rseq_flags; 62 63/* 64 * rseq feature size supported by the kernel. 0 if the registration was 65 * unsuccessful. 66 */ 67unsigned int rseq_feature_size = -1U; 68 69static int rseq_ownership; 70static int rseq_reg_success; /* At least one rseq registration has succeded. */ 71 72/* Allocate a large area for the TLS. */ 73#define RSEQ_THREAD_AREA_ALLOC_SIZE 1024 74 75/* Original struct rseq feature size is 20 bytes. */ 76#define ORIG_RSEQ_FEATURE_SIZE 20 77 78/* Original struct rseq allocation size is 32 bytes. */ 79#define ORIG_RSEQ_ALLOC_SIZE 32 80 81static 82__thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"), aligned(RSEQ_THREAD_AREA_ALLOC_SIZE))) = { 83 .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED, 84}; 85 86static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len, 87 int flags, uint32_t sig) 88{ 89 return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig); 90} 91 92static int sys_getcpu(unsigned *cpu, unsigned *node) 93{ 94 return syscall(__NR_getcpu, cpu, node, NULL); 95} 96 97int rseq_available(void) 98{ 99 int rc; 100 101 rc = sys_rseq(NULL, 0, 0, 0); 102 if (rc != -1) 103 abort(); 104 switch (errno) { 105 case ENOSYS: 106 return 0; 107 case EINVAL: 108 return 1; 109 default: 110 abort(); 111 } 112} 113 114int rseq_register_current_thread(void) 115{ 116 int rc; 117 118 if (!rseq_ownership) { 119 /* Treat libc's ownership as a successful registration. */ 120 return 0; 121 } 122 rc = sys_rseq(&__rseq_abi, rseq_size, 0, RSEQ_SIG); 123 if (rc) { 124 if (RSEQ_READ_ONCE(rseq_reg_success)) { 125 /* Incoherent success/failure within process. */ 126 abort(); 127 } 128 return -1; 129 } 130 assert(rseq_current_cpu_raw() >= 0); 131 RSEQ_WRITE_ONCE(rseq_reg_success, 1); 132 return 0; 133} 134 135int rseq_unregister_current_thread(void) 136{ 137 int rc; 138 139 if (!rseq_ownership) { 140 /* Treat libc's ownership as a successful unregistration. */ 141 return 0; 142 } 143 rc = sys_rseq(&__rseq_abi, rseq_size, RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG); 144 if (rc) 145 return -1; 146 return 0; 147} 148 149static 150unsigned int get_rseq_feature_size(void) 151{ 152 unsigned long auxv_rseq_feature_size, auxv_rseq_align; 153 154 auxv_rseq_align = getauxval(AT_RSEQ_ALIGN); 155 assert(!auxv_rseq_align || auxv_rseq_align <= RSEQ_THREAD_AREA_ALLOC_SIZE); 156 157 auxv_rseq_feature_size = getauxval(AT_RSEQ_FEATURE_SIZE); 158 assert(!auxv_rseq_feature_size || auxv_rseq_feature_size <= RSEQ_THREAD_AREA_ALLOC_SIZE); 159 if (auxv_rseq_feature_size) 160 return auxv_rseq_feature_size; 161 else 162 return ORIG_RSEQ_FEATURE_SIZE; 163} 164 165static __attribute__((constructor)) 166void rseq_init(void) 167{ 168 /* 169 * If the libc's registered rseq size isn't already valid, it may be 170 * because the binary is dynamically linked and not necessarily due to 171 * libc not having registered a restartable sequence. Try to find the 172 * symbols if that's the case. 173 */ 174 if (!*libc_rseq_size_p) { 175 libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset"); 176 libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size"); 177 libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags"); 178 } 179 if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p && 180 *libc_rseq_size_p != 0) { 181 /* rseq registration owned by glibc */ 182 rseq_offset = *libc_rseq_offset_p; 183 rseq_size = *libc_rseq_size_p; 184 rseq_flags = *libc_rseq_flags_p; 185 rseq_feature_size = get_rseq_feature_size(); 186 if (rseq_feature_size > rseq_size) 187 rseq_feature_size = rseq_size; 188 return; 189 } 190 rseq_ownership = 1; 191 if (!rseq_available()) { 192 rseq_size = 0; 193 rseq_feature_size = 0; 194 return; 195 } 196 rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer(); 197 rseq_flags = 0; 198 rseq_feature_size = get_rseq_feature_size(); 199 if (rseq_feature_size == ORIG_RSEQ_FEATURE_SIZE) 200 rseq_size = ORIG_RSEQ_ALLOC_SIZE; 201 else 202 rseq_size = RSEQ_THREAD_AREA_ALLOC_SIZE; 203} 204 205static __attribute__((destructor)) 206void rseq_exit(void) 207{ 208 if (!rseq_ownership) 209 return; 210 rseq_offset = 0; 211 rseq_size = -1U; 212 rseq_feature_size = -1U; 213 rseq_ownership = 0; 214} 215 216int32_t rseq_fallback_current_cpu(void) 217{ 218 int32_t cpu; 219 220 cpu = sched_getcpu(); 221 if (cpu < 0) { 222 perror("sched_getcpu()"); 223 abort(); 224 } 225 return cpu; 226} 227 228int32_t rseq_fallback_current_node(void) 229{ 230 uint32_t cpu_id, node_id; 231 int ret; 232 233 ret = sys_getcpu(&cpu_id, &node_id); 234 if (ret) { 235 perror("sys_getcpu()"); 236 return ret; 237 } 238 return (int32_t) node_id; 239} 240