1 /*
2 * ucontext coroutine initialization code
3 *
4 * Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
5 * Copyright (C) 2011 Kevin Wolf <kwolf@redhat.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; either
10 * version 2.0 of the License, or (at your option) any later version.
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 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
19 */
20
21 /* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
22 #ifdef _FORTIFY_SOURCE
23 #undef _FORTIFY_SOURCE
24 #endif
25 #include "qemu/osdep.h"
26 #include <ucontext.h>
27 #include "qemu/coroutine_int.h"
28
29 #ifdef CONFIG_VALGRIND_H
30 #include <valgrind/valgrind.h>
31 #endif
32
33 #if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
34 #ifdef CONFIG_ASAN_IFACE_FIBER
35 #define CONFIG_ASAN 1
36 #include <sanitizer/asan_interface.h>
37 #endif
38 #endif
39
40 #ifdef CONFIG_TSAN
41 #include <sanitizer/tsan_interface.h>
42 #endif
43
44 typedef struct {
45 Coroutine base;
46 void *stack;
47 size_t stack_size;
48 #ifdef CONFIG_SAFESTACK
49 /* Need an unsafe stack for each coroutine */
50 void *unsafe_stack;
51 size_t unsafe_stack_size;
52 #endif
53 sigjmp_buf env;
54
55 #ifdef CONFIG_TSAN
56 void *tsan_co_fiber;
57 void *tsan_caller_fiber;
58 #endif
59
60 #ifdef CONFIG_VALGRIND_H
61 unsigned int valgrind_stack_id;
62 #endif
63
64 } CoroutineUContext;
65
66 /**
67 * Per-thread coroutine bookkeeping
68 */
69 static __thread CoroutineUContext leader;
70 static __thread Coroutine *current;
71
72 /*
73 * va_args to makecontext() must be type 'int', so passing
74 * the pointer we need may require several int args. This
75 * union is a quick hack to let us do that
76 */
77 union cc_arg {
78 void *p;
79 int i[2];
80 };
81
82 /*
83 * QEMU_ALWAYS_INLINE only does so if __OPTIMIZE__, so we cannot use it.
84 * always_inline is required to avoid TSan runtime fatal errors.
85 */
86 static inline __attribute__((always_inline))
on_new_fiber(CoroutineUContext * co)87 void on_new_fiber(CoroutineUContext *co)
88 {
89 #ifdef CONFIG_TSAN
90 co->tsan_co_fiber = __tsan_create_fiber(0); /* flags: sync on switch */
91 co->tsan_caller_fiber = __tsan_get_current_fiber();
92 #endif
93 }
94
95 /* always_inline is required to avoid TSan runtime fatal errors. */
96 static inline __attribute__((always_inline))
finish_switch_fiber(void * fake_stack_save)97 void finish_switch_fiber(void *fake_stack_save)
98 {
99 #ifdef CONFIG_ASAN
100 const void *bottom_old;
101 size_t size_old;
102
103 __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
104
105 if (!leader.stack) {
106 leader.stack = (void *)bottom_old;
107 leader.stack_size = size_old;
108 }
109 #endif
110 #ifdef CONFIG_TSAN
111 if (fake_stack_save) {
112 __tsan_release(fake_stack_save);
113 __tsan_switch_to_fiber(fake_stack_save, 0); /* 0=synchronize */
114 }
115 #endif
116 }
117
118 /* always_inline is required to avoid TSan runtime fatal errors. */
119 static inline __attribute__((always_inline))
start_switch_fiber_asan(CoroutineAction action,void ** fake_stack_save,const void * bottom,size_t size)120 void start_switch_fiber_asan(CoroutineAction action, void **fake_stack_save,
121 const void *bottom, size_t size)
122 {
123 #ifdef CONFIG_ASAN
124 __sanitizer_start_switch_fiber(
125 action == COROUTINE_TERMINATE ? NULL : fake_stack_save,
126 bottom, size);
127 #endif
128 }
129
130 /* always_inline is required to avoid TSan runtime fatal errors. */
131 static inline __attribute__((always_inline))
start_switch_fiber_tsan(void ** fake_stack_save,CoroutineUContext * co,bool caller)132 void start_switch_fiber_tsan(void **fake_stack_save,
133 CoroutineUContext *co,
134 bool caller)
135 {
136 #ifdef CONFIG_TSAN
137 void *new_fiber = caller ?
138 co->tsan_caller_fiber :
139 co->tsan_co_fiber;
140 void *curr_fiber = __tsan_get_current_fiber();
141 __tsan_acquire(curr_fiber);
142
143 *fake_stack_save = curr_fiber;
144 __tsan_switch_to_fiber(new_fiber, 0); /* 0=synchronize */
145 #endif
146 }
147
coroutine_trampoline(int i0,int i1)148 static void coroutine_trampoline(int i0, int i1)
149 {
150 union cc_arg arg;
151 CoroutineUContext *self;
152 Coroutine *co;
153 void *fake_stack_save = NULL;
154
155 finish_switch_fiber(NULL);
156
157 arg.i[0] = i0;
158 arg.i[1] = i1;
159 self = arg.p;
160 co = &self->base;
161
162 /* Initialize longjmp environment and switch back the caller */
163 if (!sigsetjmp(self->env, 0)) {
164 start_switch_fiber_asan(COROUTINE_YIELD, &fake_stack_save, leader.stack,
165 leader.stack_size);
166 start_switch_fiber_tsan(&fake_stack_save, self, true); /* true=caller */
167 siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
168 }
169
170 finish_switch_fiber(fake_stack_save);
171
172 while (true) {
173 co->entry(co->entry_arg);
174 qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
175 }
176 }
177
qemu_coroutine_new(void)178 Coroutine *qemu_coroutine_new(void)
179 {
180 CoroutineUContext *co;
181 ucontext_t old_uc, uc;
182 sigjmp_buf old_env;
183 union cc_arg arg = {0};
184 void *fake_stack_save = NULL;
185
186 /* The ucontext functions preserve signal masks which incurs a
187 * system call overhead. sigsetjmp(buf, 0)/siglongjmp() does not
188 * preserve signal masks but only works on the current stack.
189 * Since we need a way to create and switch to a new stack, use
190 * the ucontext functions for that but sigsetjmp()/siglongjmp() for
191 * everything else.
192 */
193
194 if (getcontext(&uc) == -1) {
195 abort();
196 }
197
198 co = g_malloc0(sizeof(*co));
199 co->stack_size = COROUTINE_STACK_SIZE;
200 co->stack = qemu_alloc_stack(&co->stack_size);
201 #ifdef CONFIG_SAFESTACK
202 co->unsafe_stack_size = COROUTINE_STACK_SIZE;
203 co->unsafe_stack = qemu_alloc_stack(&co->unsafe_stack_size);
204 #endif
205 co->base.entry_arg = &old_env; /* stash away our jmp_buf */
206
207 uc.uc_link = &old_uc;
208 uc.uc_stack.ss_sp = co->stack;
209 uc.uc_stack.ss_size = co->stack_size;
210 uc.uc_stack.ss_flags = 0;
211
212 #ifdef CONFIG_VALGRIND_H
213 co->valgrind_stack_id =
214 VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
215 #endif
216
217 arg.p = co;
218
219 on_new_fiber(co);
220 makecontext(&uc, (void (*)(void))coroutine_trampoline,
221 2, arg.i[0], arg.i[1]);
222
223 /* swapcontext() in, siglongjmp() back out */
224 /* Save signal mask in this sigsetjmp, because makecontext on DragonFly
225 * leaves all signals blocked when entering the new context with
226 * swapcontext.
227 * Workaround this, by just having the signal mask restored by the
228 * siglongjmp that brings us back from qemu_coroutine_new().
229 * XXX Remove this workaround when the makecontext behaviour is fixed
230 * on DragonFly.
231 */
232 if (!sigsetjmp(old_env, 1)) {
233 start_switch_fiber_asan(COROUTINE_YIELD, &fake_stack_save, co->stack,
234 co->stack_size);
235 start_switch_fiber_tsan(&fake_stack_save,
236 co, false); /* false=not caller */
237
238 #ifdef CONFIG_SAFESTACK
239 /*
240 * Before we swap the context, set the new unsafe stack
241 * The unsafe stack grows just like the normal stack, so start from
242 * the last usable location of the memory area.
243 * NOTE: we don't have to re-set the usp afterwards because we are
244 * coming back to this context through a siglongjmp.
245 * The compiler already wrapped the corresponding sigsetjmp call with
246 * code that saves the usp on the (safe) stack before the call, and
247 * restores it right after (which is where we return with siglongjmp).
248 */
249 void *usp = co->unsafe_stack + co->unsafe_stack_size;
250 __safestack_unsafe_stack_ptr = usp;
251 #endif
252
253 swapcontext(&old_uc, &uc);
254 }
255
256 finish_switch_fiber(fake_stack_save);
257
258 return &co->base;
259 }
260
261 #ifdef CONFIG_VALGRIND_H
262 /* Work around an unused variable in the valgrind.h macro... */
263 #if !defined(__clang__)
264 #pragma GCC diagnostic push
265 #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
266 #endif
valgrind_stack_deregister(CoroutineUContext * co)267 static inline void valgrind_stack_deregister(CoroutineUContext *co)
268 {
269 VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
270 }
271 #if !defined(__clang__)
272 #pragma GCC diagnostic pop
273 #endif
274 #endif
275
qemu_coroutine_delete(Coroutine * co_)276 void qemu_coroutine_delete(Coroutine *co_)
277 {
278 CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
279
280 #ifdef CONFIG_VALGRIND_H
281 valgrind_stack_deregister(co);
282 #endif
283
284 qemu_free_stack(co->stack, co->stack_size);
285 #ifdef CONFIG_SAFESTACK
286 qemu_free_stack(co->unsafe_stack, co->unsafe_stack_size);
287 #endif
288 g_free(co);
289 }
290
291 /* This function is marked noinline to prevent GCC from inlining it
292 * into coroutine_trampoline(). If we allow it to do that then it
293 * hoists the code to get the address of the TLS variable "current"
294 * out of the while() loop. This is an invalid transformation because
295 * the sigsetjmp() call may be called when running thread A but
296 * return in thread B, and so we might be in a different thread
297 * context each time round the loop.
298 */
299 CoroutineAction __attribute__((noinline))
qemu_coroutine_switch(Coroutine * from_,Coroutine * to_,CoroutineAction action)300 qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
301 CoroutineAction action)
302 {
303 CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
304 CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
305 int ret;
306 void *fake_stack_save = NULL;
307
308 current = to_;
309
310 ret = sigsetjmp(from->env, 0);
311 if (ret == 0) {
312 start_switch_fiber_asan(action, &fake_stack_save, to->stack,
313 to->stack_size);
314 start_switch_fiber_tsan(&fake_stack_save,
315 to, false); /* false=not caller */
316 siglongjmp(to->env, action);
317 }
318
319 finish_switch_fiber(fake_stack_save);
320
321 return ret;
322 }
323
qemu_coroutine_self(void)324 Coroutine *qemu_coroutine_self(void)
325 {
326 if (!current) {
327 current = &leader.base;
328 }
329 #ifdef CONFIG_TSAN
330 if (!leader.tsan_co_fiber) {
331 leader.tsan_co_fiber = __tsan_get_current_fiber();
332 }
333 #endif
334 return current;
335 }
336
qemu_in_coroutine(void)337 bool qemu_in_coroutine(void)
338 {
339 return current && current->caller;
340 }
341