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