1 /*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in
12 * the documentation and/or other materials provided with the
13 * distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29 #include <pthread.h>
30
31 #include <errno.h>
32 #include <string.h>
33 #include <sys/mman.h>
34 #include <unistd.h>
35
36 #include "pthread_internal.h"
37
38 #include "private/bionic_macros.h"
39 #include "private/bionic_prctl.h"
40 #include "private/bionic_ssp.h"
41 #include "private/bionic_tls.h"
42 #include "private/libc_logging.h"
43 #include "private/ErrnoRestorer.h"
44 #include "private/ScopedPthreadMutexLocker.h"
45
46 // x86 uses segment descriptors rather than a direct pointer to TLS.
47 #if __i386__
48 #include <asm/ldt.h>
49 extern "C" __LIBC_HIDDEN__ void __init_user_desc(struct user_desc*, int, void*);
50 #endif
51
52 extern "C" int __isthreaded;
53
54 // This code is used both by each new pthread and the code that initializes the main thread.
__init_tls(pthread_internal_t * thread)55 void __init_tls(pthread_internal_t* thread) {
56 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0.
57 thread->tls[TLS_SLOT_SELF] = thread->tls;
58 thread->tls[TLS_SLOT_THREAD_ID] = thread;
59 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global.
60 thread->tls[TLS_SLOT_STACK_GUARD] = reinterpret_cast<void*>(__stack_chk_guard);
61 }
62
__init_alternate_signal_stack(pthread_internal_t * thread)63 void __init_alternate_signal_stack(pthread_internal_t* thread) {
64 // Create and set an alternate signal stack.
65 void* stack_base = mmap(NULL, SIGNAL_STACK_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
66 if (stack_base != MAP_FAILED) {
67
68 // Create a guard page to catch stack overflows in signal handlers.
69 if (mprotect(stack_base, PAGE_SIZE, PROT_NONE) == -1) {
70 munmap(stack_base, SIGNAL_STACK_SIZE);
71 return;
72 }
73 stack_t ss;
74 ss.ss_sp = reinterpret_cast<uint8_t*>(stack_base) + PAGE_SIZE;
75 ss.ss_size = SIGNAL_STACK_SIZE - PAGE_SIZE;
76 ss.ss_flags = 0;
77 sigaltstack(&ss, NULL);
78 thread->alternate_signal_stack = stack_base;
79
80 // We can only use const static allocated string for mapped region name, as Android kernel
81 // uses the string pointer directly when dumping /proc/pid/maps.
82 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack");
83 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, stack_base, PAGE_SIZE, "thread signal stack guard page");
84 }
85 }
86
__init_thread(pthread_internal_t * thread)87 int __init_thread(pthread_internal_t* thread) {
88 int error = 0;
89
90 if (__predict_true((thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) == 0)) {
91 atomic_init(&thread->join_state, THREAD_NOT_JOINED);
92 } else {
93 atomic_init(&thread->join_state, THREAD_DETACHED);
94 }
95
96 // Set the scheduling policy/priority of the thread.
97 if (thread->attr.sched_policy != SCHED_NORMAL) {
98 sched_param param;
99 param.sched_priority = thread->attr.sched_priority;
100 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) {
101 #if __LP64__
102 // For backwards compatibility reasons, we only report failures on 64-bit devices.
103 error = errno;
104 #endif
105 __libc_format_log(ANDROID_LOG_WARN, "libc",
106 "pthread_create sched_setscheduler call failed: %s", strerror(errno));
107 }
108 }
109
110 thread->cleanup_stack = NULL;
111
112 return error;
113 }
114
__create_thread_mapped_space(size_t mmap_size,size_t stack_guard_size)115 static void* __create_thread_mapped_space(size_t mmap_size, size_t stack_guard_size) {
116 // Create a new private anonymous map.
117 int prot = PROT_READ | PROT_WRITE;
118 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
119 void* space = mmap(NULL, mmap_size, prot, flags, -1, 0);
120 if (space == MAP_FAILED) {
121 __libc_format_log(ANDROID_LOG_WARN,
122 "libc",
123 "pthread_create failed: couldn't allocate %zu-bytes mapped space: %s",
124 mmap_size, strerror(errno));
125 return NULL;
126 }
127
128 // Stack is at the lower end of mapped space, stack guard region is at the lower end of stack.
129 // Set the stack guard region to PROT_NONE, so we can detect thread stack overflow.
130 if (mprotect(space, stack_guard_size, PROT_NONE) == -1) {
131 __libc_format_log(ANDROID_LOG_WARN, "libc",
132 "pthread_create failed: couldn't mprotect PROT_NONE %zu-byte stack guard region: %s",
133 stack_guard_size, strerror(errno));
134 munmap(space, mmap_size);
135 return NULL;
136 }
137 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, space, stack_guard_size, "thread stack guard page");
138
139 return space;
140 }
141
__allocate_thread(pthread_attr_t * attr,pthread_internal_t ** threadp,void ** child_stack)142 static int __allocate_thread(pthread_attr_t* attr, pthread_internal_t** threadp, void** child_stack) {
143 size_t mmap_size;
144 uint8_t* stack_top;
145
146 if (attr->stack_base == NULL) {
147 // The caller didn't provide a stack, so allocate one.
148 // Make sure the stack size and guard size are multiples of PAGE_SIZE.
149 mmap_size = BIONIC_ALIGN(attr->stack_size + sizeof(pthread_internal_t), PAGE_SIZE);
150 attr->guard_size = BIONIC_ALIGN(attr->guard_size, PAGE_SIZE);
151 attr->stack_base = __create_thread_mapped_space(mmap_size, attr->guard_size);
152 if (attr->stack_base == NULL) {
153 return EAGAIN;
154 }
155 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + mmap_size;
156 } else {
157 // Remember the mmap size is zero and we don't need to free it.
158 mmap_size = 0;
159 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + attr->stack_size;
160 }
161
162 // Mapped space(or user allocated stack) is used for:
163 // pthread_internal_t
164 // thread stack (including guard page)
165
166 // To safely access the pthread_internal_t and thread stack, we need to find a 16-byte aligned boundary.
167 stack_top = reinterpret_cast<uint8_t*>(
168 (reinterpret_cast<uintptr_t>(stack_top) - sizeof(pthread_internal_t)) & ~0xf);
169
170 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top);
171 if (mmap_size == 0) {
172 // If thread was not allocated by mmap(), it may not have been cleared to zero.
173 // So assume the worst and zero it.
174 memset(thread, 0, sizeof(pthread_internal_t));
175 }
176 attr->stack_size = stack_top - reinterpret_cast<uint8_t*>(attr->stack_base);
177
178 thread->mmap_size = mmap_size;
179 thread->attr = *attr;
180 __init_tls(thread);
181
182 *threadp = thread;
183 *child_stack = stack_top;
184 return 0;
185 }
186
__pthread_start(void * arg)187 static int __pthread_start(void* arg) {
188 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg);
189
190 // Wait for our creating thread to release us. This lets it have time to
191 // notify gdb about this thread before we start doing anything.
192 // This also provides the memory barrier needed to ensure that all memory
193 // accesses previously made by the creating thread are visible to us.
194 thread->startup_handshake_lock.lock();
195
196 __init_alternate_signal_stack(thread);
197
198 void* result = thread->start_routine(thread->start_routine_arg);
199 pthread_exit(result);
200
201 return 0;
202 }
203
204 // A dummy start routine for pthread_create failures where we've created a thread but aren't
205 // going to run user code on it. We swap out the user's start routine for this and take advantage
206 // of the regular thread teardown to free up resources.
__do_nothing(void *)207 static void* __do_nothing(void*) {
208 return NULL;
209 }
210
pthread_create(pthread_t * thread_out,pthread_attr_t const * attr,void * (* start_routine)(void *),void * arg)211 int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
212 void* (*start_routine)(void*), void* arg) {
213 ErrnoRestorer errno_restorer;
214
215 // Inform the rest of the C library that at least one thread was created.
216 __isthreaded = 1;
217
218 pthread_attr_t thread_attr;
219 if (attr == NULL) {
220 pthread_attr_init(&thread_attr);
221 } else {
222 thread_attr = *attr;
223 attr = NULL; // Prevent misuse below.
224 }
225
226 pthread_internal_t* thread = NULL;
227 void* child_stack = NULL;
228 int result = __allocate_thread(&thread_attr, &thread, &child_stack);
229 if (result != 0) {
230 return result;
231 }
232
233 // Create a lock for the thread to wait on once it starts so we can keep
234 // it from doing anything until after we notify the debugger about it
235 //
236 // This also provides the memory barrier we need to ensure that all
237 // memory accesses previously performed by this thread are visible to
238 // the new thread.
239 thread->startup_handshake_lock.init(false);
240 thread->startup_handshake_lock.lock();
241
242 thread->start_routine = start_routine;
243 thread->start_routine_arg = arg;
244
245 thread->set_cached_pid(getpid());
246
247 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
248 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID;
249 void* tls = reinterpret_cast<void*>(thread->tls);
250 #if defined(__i386__)
251 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than
252 // a pointer to the TLS itself.
253 user_desc tls_descriptor;
254 __init_user_desc(&tls_descriptor, false, tls);
255 tls = &tls_descriptor;
256 #endif
257 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid));
258 if (rc == -1) {
259 int clone_errno = errno;
260 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to
261 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a
262 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker.
263 thread->startup_handshake_lock.unlock();
264 if (thread->mmap_size != 0) {
265 munmap(thread->attr.stack_base, thread->mmap_size);
266 }
267 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno));
268 return clone_errno;
269 }
270
271 int init_errno = __init_thread(thread);
272 if (init_errno != 0) {
273 // Mark the thread detached and replace its start_routine with a no-op.
274 // Letting the thread run is the easiest way to clean up its resources.
275 atomic_store(&thread->join_state, THREAD_DETACHED);
276 __pthread_internal_add(thread);
277 thread->start_routine = __do_nothing;
278 thread->startup_handshake_lock.unlock();
279 return init_errno;
280 }
281
282 // Publish the pthread_t and unlock the mutex to let the new thread start running.
283 *thread_out = __pthread_internal_add(thread);
284 thread->startup_handshake_lock.unlock();
285
286 return 0;
287 }
288