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 47 static const ptrdiff_t *libc_rseq_offset_p = &__rseq_offset; 48 static const unsigned int *libc_rseq_size_p = &__rseq_size; 49 static const unsigned int *libc_rseq_flags_p = &__rseq_flags; 50 51 /* Offset from the thread pointer to the rseq area. */ 52 ptrdiff_t rseq_offset; 53 54 /* 55 * Size of the registered rseq area. 0 if the registration was 56 * unsuccessful. 57 */ 58 unsigned int rseq_size = -1U; 59 60 /* Flags used during rseq registration. */ 61 unsigned int rseq_flags; 62 63 static int rseq_ownership; 64 static int rseq_reg_success; /* At least one rseq registration has succeded. */ 65 66 /* Allocate a large area for the TLS. */ 67 #define RSEQ_THREAD_AREA_ALLOC_SIZE 1024 68 69 /* Original struct rseq feature size is 20 bytes. */ 70 #define ORIG_RSEQ_FEATURE_SIZE 20 71 72 /* Original struct rseq allocation size is 32 bytes. */ 73 #define ORIG_RSEQ_ALLOC_SIZE 32 74 75 static 76 __thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"), aligned(RSEQ_THREAD_AREA_ALLOC_SIZE))) = { 77 .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED, 78 }; 79 80 static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len, 81 int flags, uint32_t sig) 82 { 83 return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig); 84 } 85 86 static int sys_getcpu(unsigned *cpu, unsigned *node) 87 { 88 return syscall(__NR_getcpu, cpu, node, NULL); 89 } 90 91 int rseq_available(void) 92 { 93 int rc; 94 95 rc = sys_rseq(NULL, 0, 0, 0); 96 if (rc != -1) 97 abort(); 98 switch (errno) { 99 case ENOSYS: 100 return 0; 101 case EINVAL: 102 return 1; 103 default: 104 abort(); 105 } 106 } 107 108 /* The rseq areas need to be at least 32 bytes. */ 109 static 110 unsigned int get_rseq_min_alloc_size(void) 111 { 112 unsigned int alloc_size = rseq_size; 113 114 if (alloc_size < ORIG_RSEQ_ALLOC_SIZE) 115 alloc_size = ORIG_RSEQ_ALLOC_SIZE; 116 return alloc_size; 117 } 118 119 /* 120 * Return the feature size supported by the kernel. 121 * 122 * Depending on the value returned by getauxval(AT_RSEQ_FEATURE_SIZE): 123 * 124 * 0: Return ORIG_RSEQ_FEATURE_SIZE (20) 125 * > 0: Return the value from getauxval(AT_RSEQ_FEATURE_SIZE). 126 * 127 * It should never return a value below ORIG_RSEQ_FEATURE_SIZE. 128 */ 129 static 130 unsigned int get_rseq_kernel_feature_size(void) 131 { 132 unsigned long auxv_rseq_feature_size, auxv_rseq_align; 133 134 auxv_rseq_align = getauxval(AT_RSEQ_ALIGN); 135 assert(!auxv_rseq_align || auxv_rseq_align <= RSEQ_THREAD_AREA_ALLOC_SIZE); 136 137 auxv_rseq_feature_size = getauxval(AT_RSEQ_FEATURE_SIZE); 138 assert(!auxv_rseq_feature_size || auxv_rseq_feature_size <= RSEQ_THREAD_AREA_ALLOC_SIZE); 139 if (auxv_rseq_feature_size) 140 return auxv_rseq_feature_size; 141 else 142 return ORIG_RSEQ_FEATURE_SIZE; 143 } 144 145 int rseq_register_current_thread(void) 146 { 147 int rc; 148 149 if (!rseq_ownership) { 150 /* Treat libc's ownership as a successful registration. */ 151 return 0; 152 } 153 rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), 0, RSEQ_SIG); 154 if (rc) { 155 if (RSEQ_READ_ONCE(rseq_reg_success)) { 156 /* Incoherent success/failure within process. */ 157 abort(); 158 } 159 return -1; 160 } 161 assert(rseq_current_cpu_raw() >= 0); 162 RSEQ_WRITE_ONCE(rseq_reg_success, 1); 163 return 0; 164 } 165 166 int rseq_unregister_current_thread(void) 167 { 168 int rc; 169 170 if (!rseq_ownership) { 171 /* Treat libc's ownership as a successful unregistration. */ 172 return 0; 173 } 174 rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG); 175 if (rc) 176 return -1; 177 return 0; 178 } 179 180 static __attribute__((constructor)) 181 void rseq_init(void) 182 { 183 /* 184 * If the libc's registered rseq size isn't already valid, it may be 185 * because the binary is dynamically linked and not necessarily due to 186 * libc not having registered a restartable sequence. Try to find the 187 * symbols if that's the case. 188 */ 189 if (!*libc_rseq_size_p) { 190 libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset"); 191 libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size"); 192 libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags"); 193 } 194 if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p && 195 *libc_rseq_size_p != 0) { 196 unsigned int libc_rseq_size; 197 198 /* rseq registration owned by glibc */ 199 rseq_offset = *libc_rseq_offset_p; 200 libc_rseq_size = *libc_rseq_size_p; 201 rseq_flags = *libc_rseq_flags_p; 202 203 /* 204 * Previous versions of glibc expose the value 205 * 32 even though the kernel only supported 20 206 * bytes initially. Therefore treat 32 as a 207 * special-case. glibc 2.40 exposes a 20 bytes 208 * __rseq_size without using getauxval(3) to 209 * query the supported size, while still allocating a 32 210 * bytes area. Also treat 20 as a special-case. 211 * 212 * Special-cases are handled by using the following 213 * value as active feature set size: 214 * 215 * rseq_size = min(32, get_rseq_kernel_feature_size()) 216 */ 217 switch (libc_rseq_size) { 218 case ORIG_RSEQ_FEATURE_SIZE: 219 fallthrough; 220 case ORIG_RSEQ_ALLOC_SIZE: 221 { 222 unsigned int rseq_kernel_feature_size = get_rseq_kernel_feature_size(); 223 224 if (rseq_kernel_feature_size < ORIG_RSEQ_ALLOC_SIZE) 225 rseq_size = rseq_kernel_feature_size; 226 else 227 rseq_size = ORIG_RSEQ_ALLOC_SIZE; 228 break; 229 } 230 default: 231 /* Otherwise just use the __rseq_size from libc as rseq_size. */ 232 rseq_size = libc_rseq_size; 233 break; 234 } 235 return; 236 } 237 rseq_ownership = 1; 238 if (!rseq_available()) { 239 rseq_size = 0; 240 return; 241 } 242 rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer(); 243 rseq_flags = 0; 244 } 245 246 static __attribute__((destructor)) 247 void rseq_exit(void) 248 { 249 if (!rseq_ownership) 250 return; 251 rseq_offset = 0; 252 rseq_size = -1U; 253 rseq_ownership = 0; 254 } 255 256 int32_t rseq_fallback_current_cpu(void) 257 { 258 int32_t cpu; 259 260 cpu = sched_getcpu(); 261 if (cpu < 0) { 262 perror("sched_getcpu()"); 263 abort(); 264 } 265 return cpu; 266 } 267 268 int32_t rseq_fallback_current_node(void) 269 { 270 uint32_t cpu_id, node_id; 271 int ret; 272 273 ret = sys_getcpu(&cpu_id, &node_id); 274 if (ret) { 275 perror("sys_getcpu()"); 276 return ret; 277 } 278 return (int32_t) node_id; 279 } 280