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 65 /* Allocate a large area for the TLS. */ 66 #define RSEQ_THREAD_AREA_ALLOC_SIZE 1024 67 68 /* Original struct rseq feature size is 20 bytes. */ 69 #define ORIG_RSEQ_FEATURE_SIZE 20 70 71 /* Original struct rseq allocation size is 32 bytes. */ 72 #define ORIG_RSEQ_ALLOC_SIZE 32 73 74 static 75 __thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"), aligned(RSEQ_THREAD_AREA_ALLOC_SIZE))) = { 76 .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED, 77 }; 78 79 static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len, 80 int flags, uint32_t sig) 81 { 82 return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig); 83 } 84 85 static int sys_getcpu(unsigned *cpu, unsigned *node) 86 { 87 return syscall(__NR_getcpu, cpu, node, NULL); 88 } 89 90 int rseq_available(void) 91 { 92 int rc; 93 94 rc = sys_rseq(NULL, 0, 0, 0); 95 if (rc != -1) 96 abort(); 97 switch (errno) { 98 case ENOSYS: 99 return 0; 100 case EINVAL: 101 return 1; 102 default: 103 abort(); 104 } 105 } 106 107 /* The rseq areas need to be at least 32 bytes. */ 108 static 109 unsigned int get_rseq_min_alloc_size(void) 110 { 111 unsigned int alloc_size = rseq_size; 112 113 if (alloc_size < ORIG_RSEQ_ALLOC_SIZE) 114 alloc_size = ORIG_RSEQ_ALLOC_SIZE; 115 return alloc_size; 116 } 117 118 /* 119 * Return the feature size supported by the kernel. 120 * 121 * Depending on the value returned by getauxval(AT_RSEQ_FEATURE_SIZE): 122 * 123 * 0: Return ORIG_RSEQ_FEATURE_SIZE (20) 124 * > 0: Return the value from getauxval(AT_RSEQ_FEATURE_SIZE). 125 * 126 * It should never return a value below ORIG_RSEQ_FEATURE_SIZE. 127 */ 128 static 129 unsigned int get_rseq_kernel_feature_size(void) 130 { 131 unsigned long auxv_rseq_feature_size, auxv_rseq_align; 132 133 auxv_rseq_align = getauxval(AT_RSEQ_ALIGN); 134 assert(!auxv_rseq_align || auxv_rseq_align <= RSEQ_THREAD_AREA_ALLOC_SIZE); 135 136 auxv_rseq_feature_size = getauxval(AT_RSEQ_FEATURE_SIZE); 137 assert(!auxv_rseq_feature_size || auxv_rseq_feature_size <= RSEQ_THREAD_AREA_ALLOC_SIZE); 138 if (auxv_rseq_feature_size) 139 return auxv_rseq_feature_size; 140 else 141 return ORIG_RSEQ_FEATURE_SIZE; 142 } 143 144 int rseq_register_current_thread(void) 145 { 146 int rc; 147 148 if (!rseq_ownership) { 149 /* Treat libc's ownership as a successful registration. */ 150 return 0; 151 } 152 rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), 0, RSEQ_SIG); 153 if (rc) { 154 /* 155 * After at least one thread has registered successfully 156 * (rseq_size > 0), the registration of other threads should 157 * never fail. 158 */ 159 if (RSEQ_READ_ONCE(rseq_size) > 0) { 160 /* Incoherent success/failure within process. */ 161 abort(); 162 } 163 return -1; 164 } 165 assert(rseq_current_cpu_raw() >= 0); 166 167 /* 168 * The first thread to register sets the rseq_size to mimic the libc 169 * behavior. 170 */ 171 if (RSEQ_READ_ONCE(rseq_size) == 0) { 172 RSEQ_WRITE_ONCE(rseq_size, get_rseq_kernel_feature_size()); 173 } 174 175 return 0; 176 } 177 178 int rseq_unregister_current_thread(void) 179 { 180 int rc; 181 182 if (!rseq_ownership) { 183 /* Treat libc's ownership as a successful unregistration. */ 184 return 0; 185 } 186 rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG); 187 if (rc) 188 return -1; 189 return 0; 190 } 191 192 static __attribute__((constructor)) 193 void rseq_init(void) 194 { 195 /* 196 * If the libc's registered rseq size isn't already valid, it may be 197 * because the binary is dynamically linked and not necessarily due to 198 * libc not having registered a restartable sequence. Try to find the 199 * symbols if that's the case. 200 */ 201 if (!*libc_rseq_size_p) { 202 libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset"); 203 libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size"); 204 libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags"); 205 } 206 if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p && 207 *libc_rseq_size_p != 0) { 208 unsigned int libc_rseq_size; 209 210 /* rseq registration owned by glibc */ 211 rseq_offset = *libc_rseq_offset_p; 212 libc_rseq_size = *libc_rseq_size_p; 213 rseq_flags = *libc_rseq_flags_p; 214 215 /* 216 * Previous versions of glibc expose the value 217 * 32 even though the kernel only supported 20 218 * bytes initially. Therefore treat 32 as a 219 * special-case. glibc 2.40 exposes a 20 bytes 220 * __rseq_size without using getauxval(3) to 221 * query the supported size, while still allocating a 32 222 * bytes area. Also treat 20 as a special-case. 223 * 224 * Special-cases are handled by using the following 225 * value as active feature set size: 226 * 227 * rseq_size = min(32, get_rseq_kernel_feature_size()) 228 */ 229 switch (libc_rseq_size) { 230 case ORIG_RSEQ_FEATURE_SIZE: 231 fallthrough; 232 case ORIG_RSEQ_ALLOC_SIZE: 233 { 234 unsigned int rseq_kernel_feature_size = get_rseq_kernel_feature_size(); 235 236 if (rseq_kernel_feature_size < ORIG_RSEQ_ALLOC_SIZE) 237 rseq_size = rseq_kernel_feature_size; 238 else 239 rseq_size = ORIG_RSEQ_ALLOC_SIZE; 240 break; 241 } 242 default: 243 /* Otherwise just use the __rseq_size from libc as rseq_size. */ 244 rseq_size = libc_rseq_size; 245 break; 246 } 247 return; 248 } 249 rseq_ownership = 1; 250 251 /* Calculate the offset of the rseq area from the thread pointer. */ 252 rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer(); 253 254 /* rseq flags are deprecated, always set to 0. */ 255 rseq_flags = 0; 256 257 /* 258 * Set the size to 0 until at least one thread registers to mimic the 259 * libc behavior. 260 */ 261 rseq_size = 0; 262 } 263 264 static __attribute__((destructor)) 265 void rseq_exit(void) 266 { 267 if (!rseq_ownership) 268 return; 269 rseq_offset = 0; 270 rseq_size = -1U; 271 rseq_ownership = 0; 272 } 273 274 int32_t rseq_fallback_current_cpu(void) 275 { 276 int32_t cpu; 277 278 cpu = sched_getcpu(); 279 if (cpu < 0) { 280 perror("sched_getcpu()"); 281 abort(); 282 } 283 return cpu; 284 } 285 286 int32_t rseq_fallback_current_node(void) 287 { 288 uint32_t cpu_id, node_id; 289 int ret; 290 291 ret = sys_getcpu(&cpu_id, &node_id); 292 if (ret) { 293 perror("sys_getcpu()"); 294 return ret; 295 } 296 return (int32_t) node_id; 297 } 298