1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
4 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
5 * Copyright (C) 2004 PathScale, Inc
6 * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
7 */
8
9#include <stdlib.h>
10#include <stdarg.h>
11#include <stdbool.h>
12#include <errno.h>
13#include <signal.h>
14#include <string.h>
15#include <strings.h>
16#include <as-layout.h>
17#include <kern_util.h>
18#include <os.h>
19#include <sysdep/mcontext.h>
20#include <um_malloc.h>
21#include <sys/ucontext.h>
22#include <timetravel.h>
23#include "internal.h"
24
25void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *, void *mc) = {
26 [SIGTRAP] = relay_signal,
27 [SIGFPE] = relay_signal,
28 [SIGILL] = relay_signal,
29 [SIGWINCH] = winch,
30 [SIGBUS] = relay_signal,
31 [SIGSEGV] = segv_handler,
32 [SIGIO] = sigio_handler,
33 [SIGCHLD] = sigchld_handler,
34};
35
36static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
37{
38 struct uml_pt_regs r;
39 int save_errno = errno;
40
41 r.is_user = 0;
42 if (sig == SIGSEGV) {
43 /* For segfaults, we want the data from the sigcontext. */
44 get_regs_from_mc(&r, mc);
45 GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
46 }
47
48 /* enable signals if sig isn't IRQ signal */
49 if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGCHLD))
50 unblock_signals_trace();
51
52 (*sig_info[sig])(sig, si, &r, mc);
53
54 errno = save_errno;
55}
56
57/*
58 * These are the asynchronous signals. SIGPROF is excluded because we want to
59 * be able to profile all of UML, not just the non-critical sections. If
60 * profiling is not thread-safe, then that is not my problem. We can disable
61 * profiling when SMP is enabled in that case.
62 */
63#define SIGIO_BIT 0
64#define SIGIO_MASK (1 << SIGIO_BIT)
65
66#define SIGALRM_BIT 1
67#define SIGALRM_MASK (1 << SIGALRM_BIT)
68
69#define SIGCHLD_BIT 2
70#define SIGCHLD_MASK (1 << SIGCHLD_BIT)
71
72__thread int signals_enabled;
73#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
74static int signals_blocked, signals_blocked_pending;
75#endif
76static __thread unsigned int signals_pending;
77static __thread unsigned int signals_active;
78
79static void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
80{
81 int enabled = signals_enabled;
82
83#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
84 if ((signals_blocked ||
85 __atomic_load_n(&signals_blocked_pending, __ATOMIC_SEQ_CST)) &&
86 (sig == SIGIO)) {
87 /* increment so unblock will do another round */
88 __atomic_add_fetch(&signals_blocked_pending, 1,
89 __ATOMIC_SEQ_CST);
90 return;
91 }
92#endif
93
94 if (!enabled && (sig == SIGIO)) {
95 /*
96 * In TT_MODE_EXTERNAL, need to still call time-travel
97 * handlers. This will mark signals_pending by itself
98 * (only if necessary.)
99 * Note we won't get here if signals are hard-blocked
100 * (which is handled above), in that case the hard-
101 * unblock will handle things.
102 */
103 if (time_travel_mode == TT_MODE_EXTERNAL)
104 sigio_run_timetravel_handlers();
105 else
106 signals_pending |= SIGIO_MASK;
107 return;
108 }
109
110 if (!enabled && (sig == SIGCHLD)) {
111 signals_pending |= SIGCHLD_MASK;
112 return;
113 }
114
115 block_signals_trace();
116
117 sig_handler_common(sig, si, mc);
118
119 um_set_signals_trace(enabled);
120}
121
122static void timer_real_alarm_handler(mcontext_t *mc)
123{
124 struct uml_pt_regs regs;
125
126 if (mc != NULL)
127 get_regs_from_mc(&regs, mc);
128 else
129 memset(&regs, 0, sizeof(regs));
130 timer_handler(SIGALRM, NULL, &regs);
131}
132
133static void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
134{
135 int enabled;
136
137 enabled = signals_enabled;
138 if (!signals_enabled) {
139 signals_pending |= SIGALRM_MASK;
140 return;
141 }
142
143 block_signals_trace();
144
145 signals_active |= SIGALRM_MASK;
146
147 timer_real_alarm_handler(mc);
148
149 signals_active &= ~SIGALRM_MASK;
150
151 um_set_signals_trace(enabled);
152}
153
154void deliver_alarm(void) {
155 timer_alarm_handler(SIGALRM, NULL, NULL);
156}
157
158void timer_set_signal_handler(void)
159{
160 set_handler(SIGALRM);
161}
162
163int timer_alarm_pending(void)
164{
165 return !!(signals_pending & SIGALRM_MASK);
166}
167
168void set_sigstack(void *sig_stack, int size)
169{
170 stack_t stack = {
171 .ss_flags = 0,
172 .ss_sp = sig_stack,
173 .ss_size = size
174 };
175
176 if (sigaltstack(&stack, NULL) != 0)
177 panic("enabling signal stack failed, errno = %d\n", errno);
178}
179
180static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
181{
182 uml_pm_wake();
183}
184
185void register_pm_wake_signal(void)
186{
187 set_handler(SIGUSR1);
188}
189
190static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
191 [SIGSEGV] = sig_handler,
192 [SIGBUS] = sig_handler,
193 [SIGILL] = sig_handler,
194 [SIGFPE] = sig_handler,
195 [SIGTRAP] = sig_handler,
196
197 [SIGIO] = sig_handler,
198 [SIGWINCH] = sig_handler,
199 /* SIGCHLD is only actually registered in seccomp mode. */
200 [SIGCHLD] = sig_handler,
201 [SIGALRM] = timer_alarm_handler,
202
203 [SIGUSR1] = sigusr1_handler,
204};
205
206static void hard_handler(int sig, siginfo_t *si, void *p)
207{
208 ucontext_t *uc = p;
209 mcontext_t *mc = &uc->uc_mcontext;
210
211 (*handlers[sig])(sig, (struct siginfo *)si, mc);
212}
213
214void set_handler(int sig)
215{
216 struct sigaction action;
217 int flags = SA_SIGINFO | SA_ONSTACK;
218 sigset_t sig_mask;
219
220 action.sa_sigaction = hard_handler;
221
222 /* block irq ones */
223 sigemptyset(&action.sa_mask);
224 sigaddset(&action.sa_mask, SIGIO);
225 sigaddset(&action.sa_mask, SIGWINCH);
226 sigaddset(&action.sa_mask, SIGALRM);
227
228 if (sig == SIGSEGV)
229 flags |= SA_NODEFER;
230
231 if (sigismember(&action.sa_mask, sig))
232 flags |= SA_RESTART; /* if it's an irq signal */
233
234 action.sa_flags = flags;
235 action.sa_restorer = NULL;
236 if (sigaction(sig, &action, NULL) < 0)
237 panic("sigaction failed - errno = %d\n", errno);
238
239 sigemptyset(&sig_mask);
240 sigaddset(&sig_mask, sig);
241 if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
242 panic("sigprocmask failed - errno = %d\n", errno);
243}
244
245void send_sigio_to_self(void)
246{
247 kill(os_getpid(), SIGIO);
248}
249
250int change_sig(int signal, int on)
251{
252 sigset_t sigset;
253
254 sigemptyset(&sigset);
255 sigaddset(&sigset, signal);
256 if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
257 return -errno;
258
259 return 0;
260}
261
262static inline void __block_signals(void)
263{
264 if (!signals_enabled)
265 return;
266
267 os_local_ipi_disable();
268 barrier();
269 signals_enabled = 0;
270}
271
272static inline void __unblock_signals(void)
273{
274 if (signals_enabled)
275 return;
276
277 signals_enabled = 1;
278 barrier();
279 os_local_ipi_enable();
280}
281
282void block_signals(void)
283{
284 __block_signals();
285 /*
286 * This must return with signals disabled, so this barrier
287 * ensures that writes are flushed out before the return.
288 * This might matter if gcc figures out how to inline this and
289 * decides to shuffle this code into the caller.
290 */
291 barrier();
292}
293
294void unblock_signals(void)
295{
296 int save_pending;
297
298 if (signals_enabled == 1)
299 return;
300
301 __unblock_signals();
302
303#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
304 deliver_time_travel_irqs();
305#endif
306
307 /*
308 * We loop because the IRQ handler returns with interrupts off. So,
309 * interrupts may have arrived and we need to re-enable them and
310 * recheck signals_pending.
311 */
312 while (1) {
313 /*
314 * Save and reset save_pending after enabling signals. This
315 * way, signals_pending won't be changed while we're reading it.
316 *
317 * Setting signals_enabled and reading signals_pending must
318 * happen in this order, so have the barrier here.
319 */
320 barrier();
321
322 save_pending = signals_pending;
323 if (save_pending == 0)
324 return;
325
326 signals_pending = 0;
327
328 /*
329 * We have pending interrupts, so disable signals, as the
330 * handlers expect them off when they are called. They will
331 * be enabled again above. We need to trace this, as we're
332 * expected to be enabling interrupts already, but any more
333 * tracing that happens inside the handlers we call for the
334 * pending signals will mess up the tracing state.
335 */
336 __block_signals();
337 um_trace_signals_off();
338
339 /*
340 * Deal with SIGIO first because the alarm handler might
341 * schedule, leaving the pending SIGIO stranded until we come
342 * back here.
343 *
344 * SIGIO's handler doesn't use siginfo or mcontext,
345 * so they can be NULL.
346 */
347 if (save_pending & SIGIO_MASK)
348 sig_handler_common(SIGIO, NULL, NULL);
349
350 if (save_pending & SIGCHLD_MASK) {
351 struct uml_pt_regs regs = {};
352
353 sigchld_handler(SIGCHLD, NULL, &regs, NULL);
354 }
355
356 /* Do not reenter the handler */
357
358 if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
359 timer_real_alarm_handler(NULL);
360
361 /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
362
363 if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
364 return;
365
366 /* Re-enable signals and trace that we're doing so. */
367 um_trace_signals_on();
368 __unblock_signals();
369 }
370}
371
372int um_get_signals(void)
373{
374 return signals_enabled;
375}
376
377int um_set_signals(int enable)
378{
379 int ret;
380 if (signals_enabled == enable)
381 return enable;
382
383 ret = signals_enabled;
384 if (enable)
385 unblock_signals();
386 else block_signals();
387
388 return ret;
389}
390
391int um_set_signals_trace(int enable)
392{
393 int ret;
394 if (signals_enabled == enable)
395 return enable;
396
397 ret = signals_enabled;
398 if (enable)
399 unblock_signals_trace();
400 else
401 block_signals_trace();
402
403 return ret;
404}
405
406#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
407void mark_sigio_pending(void)
408{
409 /*
410 * It would seem that this should be atomic so
411 * it isn't a read-modify-write with a signal
412 * that could happen in the middle, losing the
413 * value set by the signal.
414 *
415 * However, this function is only called when in
416 * time-travel=ext simulation mode, in which case
417 * the only signal ever pending is SIGIO, which
418 * is blocked while this can be called, and the
419 * timer signal (SIGALRM) cannot happen.
420 */
421 signals_pending |= SIGIO_MASK;
422}
423
424void block_signals_hard(void)
425{
426 signals_blocked++;
427 barrier();
428}
429
430void unblock_signals_hard(void)
431{
432 static bool unblocking;
433
434 if (!signals_blocked)
435 panic("unblocking signals while not blocked");
436
437 if (--signals_blocked)
438 return;
439 /*
440 * Must be set to 0 before we check pending so the
441 * SIGIO handler will run as normal unless we're still
442 * going to process signals_blocked_pending.
443 */
444 barrier();
445
446 /*
447 * Note that block_signals_hard()/unblock_signals_hard() can be called
448 * within the unblock_signals()/sigio_run_timetravel_handlers() below.
449 * This would still be prone to race conditions since it's actually a
450 * call _within_ e.g. vu_req_read_message(), where we observed this
451 * issue, which loops. Thus, if the inner call handles the recorded
452 * pending signals, we can get out of the inner call with the real
453 * signal hander no longer blocked, and still have a race. Thus don't
454 * handle unblocking in the inner call, if it happens, but only in
455 * the outermost call - 'unblocking' serves as an ownership for the
456 * signals_blocked_pending decrement.
457 */
458 if (unblocking)
459 return;
460 unblocking = true;
461
462 while (__atomic_load_n(&signals_blocked_pending, __ATOMIC_SEQ_CST)) {
463 if (signals_enabled) {
464 /* signals are enabled so we can touch this */
465 signals_pending |= SIGIO_MASK;
466 /*
467 * this is a bit inefficient, but that's
468 * not really important
469 */
470 block_signals();
471 unblock_signals();
472 } else {
473 /*
474 * we need to run time-travel handlers even
475 * if not enabled
476 */
477 sigio_run_timetravel_handlers();
478 }
479
480 /*
481 * The decrement of signals_blocked_pending must be atomic so
482 * that the signal handler will either happen before or after
483 * the decrement, not during a read-modify-write:
484 * - If it happens before, it can increment it and we'll
485 * decrement it and do another round in the loop.
486 * - If it happens after it'll see 0 for both signals_blocked
487 * and signals_blocked_pending and thus run the handler as
488 * usual (subject to signals_enabled, but that's unrelated.)
489 *
490 * Note that a call to unblock_signals_hard() within the calls
491 * to unblock_signals() or sigio_run_timetravel_handlers() above
492 * will do nothing due to the 'unblocking' state, so this cannot
493 * underflow as the only one decrementing will be the outermost
494 * one.
495 */
496 if (__atomic_sub_fetch(&signals_blocked_pending, 1,
497 __ATOMIC_SEQ_CST) < 0)
498 panic("signals_blocked_pending underflow");
499 }
500
501 unblocking = false;
502}
503#endif
504

source code of linux/arch/um/os-Linux/signal.c