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 <errno.h>
12 #include <signal.h>
13 #include <string.h>
14 #include <strings.h>
15 #include <as-layout.h>
16 #include <kern_util.h>
17 #include <os.h>
18 #include <sysdep/mcontext.h>
19 #include <um_malloc.h>
20 #include <sys/ucontext.h>
21 #include <timetravel.h>
22 
23 void (*sig_info[NSIG])(int, struct siginfo *, 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 };
32 
sig_handler_common(int sig,struct siginfo * si,mcontext_t * mc)33 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
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 		get_regs_from_mc(&r, mc);
42 		GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
43 	}
44 
45 	/* enable signals if sig isn't IRQ signal */
46 	if ((sig != SIGIO) && (sig != SIGWINCH))
47 		unblock_signals_trace();
48 
49 	(*sig_info[sig])(sig, si, &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 SIGALRM_BIT 1
64 #define SIGALRM_MASK (1 << SIGALRM_BIT)
65 
66 int signals_enabled;
67 #ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT
68 static int signals_blocked;
69 #else
70 #define signals_blocked 0
71 #endif
72 static unsigned int signals_pending;
73 static unsigned int signals_active = 0;
74 
sig_handler(int sig,struct siginfo * si,mcontext_t * mc)75 void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
76 {
77 	int enabled = signals_enabled;
78 
79 	if ((signals_blocked || !enabled) && (sig == SIGIO)) {
80 		/*
81 		 * In TT_MODE_EXTERNAL, need to still call time-travel
82 		 * handlers unless signals are also blocked for the
83 		 * external time message processing. This will mark
84 		 * signals_pending by itself (only if necessary.)
85 		 */
86 		if (!signals_blocked && time_travel_mode == TT_MODE_EXTERNAL)
87 			sigio_run_timetravel_handlers();
88 		else
89 			signals_pending |= SIGIO_MASK;
90 		return;
91 	}
92 
93 	block_signals_trace();
94 
95 	sig_handler_common(sig, si, mc);
96 
97 	um_set_signals_trace(enabled);
98 }
99 
timer_real_alarm_handler(mcontext_t * mc)100 static void timer_real_alarm_handler(mcontext_t *mc)
101 {
102 	struct uml_pt_regs regs;
103 
104 	if (mc != NULL)
105 		get_regs_from_mc(&regs, mc);
106 	else
107 		memset(&regs, 0, sizeof(regs));
108 	timer_handler(SIGALRM, NULL, &regs);
109 }
110 
timer_alarm_handler(int sig,struct siginfo * unused_si,mcontext_t * mc)111 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
112 {
113 	int enabled;
114 
115 	enabled = signals_enabled;
116 	if (!signals_enabled) {
117 		signals_pending |= SIGALRM_MASK;
118 		return;
119 	}
120 
121 	block_signals_trace();
122 
123 	signals_active |= SIGALRM_MASK;
124 
125 	timer_real_alarm_handler(mc);
126 
127 	signals_active &= ~SIGALRM_MASK;
128 
129 	um_set_signals_trace(enabled);
130 }
131 
deliver_alarm(void)132 void deliver_alarm(void) {
133     timer_alarm_handler(SIGALRM, NULL, NULL);
134 }
135 
timer_set_signal_handler(void)136 void timer_set_signal_handler(void)
137 {
138 	set_handler(SIGALRM);
139 }
140 
set_sigstack(void * sig_stack,int size)141 void set_sigstack(void *sig_stack, int size)
142 {
143 	stack_t stack = {
144 		.ss_flags = 0,
145 		.ss_sp = sig_stack,
146 		.ss_size = size
147 	};
148 
149 	if (sigaltstack(&stack, NULL) != 0)
150 		panic("enabling signal stack failed, errno = %d\n", errno);
151 }
152 
sigusr1_handler(int sig,struct siginfo * unused_si,mcontext_t * mc)153 static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
154 {
155 	uml_pm_wake();
156 }
157 
register_pm_wake_signal(void)158 void register_pm_wake_signal(void)
159 {
160 	set_handler(SIGUSR1);
161 }
162 
163 static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
164 	[SIGSEGV] = sig_handler,
165 	[SIGBUS] = sig_handler,
166 	[SIGILL] = sig_handler,
167 	[SIGFPE] = sig_handler,
168 	[SIGTRAP] = sig_handler,
169 
170 	[SIGIO] = sig_handler,
171 	[SIGWINCH] = sig_handler,
172 	[SIGALRM] = timer_alarm_handler,
173 
174 	[SIGUSR1] = sigusr1_handler,
175 };
176 
hard_handler(int sig,siginfo_t * si,void * p)177 static void hard_handler(int sig, siginfo_t *si, void *p)
178 {
179 	ucontext_t *uc = p;
180 	mcontext_t *mc = &uc->uc_mcontext;
181 	unsigned long pending = 1UL << sig;
182 
183 	do {
184 		int nested, bail;
185 
186 		/*
187 		 * pending comes back with one bit set for each
188 		 * interrupt that arrived while setting up the stack,
189 		 * plus a bit for this interrupt, plus the zero bit is
190 		 * set if this is a nested interrupt.
191 		 * If bail is true, then we interrupted another
192 		 * handler setting up the stack.  In this case, we
193 		 * have to return, and the upper handler will deal
194 		 * with this interrupt.
195 		 */
196 		bail = to_irq_stack(&pending);
197 		if (bail)
198 			return;
199 
200 		nested = pending & 1;
201 		pending &= ~1;
202 
203 		while ((sig = ffs(pending)) != 0){
204 			sig--;
205 			pending &= ~(1 << sig);
206 			(*handlers[sig])(sig, (struct siginfo *)si, mc);
207 		}
208 
209 		/*
210 		 * Again, pending comes back with a mask of signals
211 		 * that arrived while tearing down the stack.  If this
212 		 * is non-zero, we just go back, set up the stack
213 		 * again, and handle the new interrupts.
214 		 */
215 		if (!nested)
216 			pending = from_irq_stack(nested);
217 	} while (pending);
218 }
219 
set_handler(int sig)220 void set_handler(int sig)
221 {
222 	struct sigaction action;
223 	int flags = SA_SIGINFO | SA_ONSTACK;
224 	sigset_t sig_mask;
225 
226 	action.sa_sigaction = hard_handler;
227 
228 	/* block irq ones */
229 	sigemptyset(&action.sa_mask);
230 	sigaddset(&action.sa_mask, SIGIO);
231 	sigaddset(&action.sa_mask, SIGWINCH);
232 	sigaddset(&action.sa_mask, SIGALRM);
233 
234 	if (sig == SIGSEGV)
235 		flags |= SA_NODEFER;
236 
237 	if (sigismember(&action.sa_mask, sig))
238 		flags |= SA_RESTART; /* if it's an irq signal */
239 
240 	action.sa_flags = flags;
241 	action.sa_restorer = NULL;
242 	if (sigaction(sig, &action, NULL) < 0)
243 		panic("sigaction failed - errno = %d\n", errno);
244 
245 	sigemptyset(&sig_mask);
246 	sigaddset(&sig_mask, sig);
247 	if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
248 		panic("sigprocmask failed - errno = %d\n", errno);
249 }
250 
send_sigio_to_self(void)251 void send_sigio_to_self(void)
252 {
253 	kill(os_getpid(), SIGIO);
254 }
255 
change_sig(int signal,int on)256 int change_sig(int signal, int on)
257 {
258 	sigset_t sigset;
259 
260 	sigemptyset(&sigset);
261 	sigaddset(&sigset, signal);
262 	if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
263 		return -errno;
264 
265 	return 0;
266 }
267 
block_signals(void)268 void block_signals(void)
269 {
270 	signals_enabled = 0;
271 	/*
272 	 * This must return with signals disabled, so this barrier
273 	 * ensures that writes are flushed out before the return.
274 	 * This might matter if gcc figures out how to inline this and
275 	 * decides to shuffle this code into the caller.
276 	 */
277 	barrier();
278 }
279 
unblock_signals(void)280 void unblock_signals(void)
281 {
282 	int save_pending;
283 
284 	if (signals_enabled == 1)
285 		return;
286 
287 	signals_enabled = 1;
288 #ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT
289 	deliver_time_travel_irqs();
290 #endif
291 
292 	/*
293 	 * We loop because the IRQ handler returns with interrupts off.  So,
294 	 * interrupts may have arrived and we need to re-enable them and
295 	 * recheck signals_pending.
296 	 */
297 	while (1) {
298 		/*
299 		 * Save and reset save_pending after enabling signals.  This
300 		 * way, signals_pending won't be changed while we're reading it.
301 		 *
302 		 * Setting signals_enabled and reading signals_pending must
303 		 * happen in this order, so have the barrier here.
304 		 */
305 		barrier();
306 
307 		save_pending = signals_pending;
308 		if (save_pending == 0)
309 			return;
310 
311 		signals_pending = 0;
312 
313 		/*
314 		 * We have pending interrupts, so disable signals, as the
315 		 * handlers expect them off when they are called.  They will
316 		 * be enabled again above. We need to trace this, as we're
317 		 * expected to be enabling interrupts already, but any more
318 		 * tracing that happens inside the handlers we call for the
319 		 * pending signals will mess up the tracing state.
320 		 */
321 		signals_enabled = 0;
322 		um_trace_signals_off();
323 
324 		/*
325 		 * Deal with SIGIO first because the alarm handler might
326 		 * schedule, leaving the pending SIGIO stranded until we come
327 		 * back here.
328 		 *
329 		 * SIGIO's handler doesn't use siginfo or mcontext,
330 		 * so they can be NULL.
331 		 */
332 		if (save_pending & SIGIO_MASK)
333 			sig_handler_common(SIGIO, NULL, NULL);
334 
335 		/* Do not reenter the handler */
336 
337 		if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
338 			timer_real_alarm_handler(NULL);
339 
340 		/* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
341 
342 		if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
343 			return;
344 
345 		/* Re-enable signals and trace that we're doing so. */
346 		um_trace_signals_on();
347 		signals_enabled = 1;
348 	}
349 }
350 
um_set_signals(int enable)351 int um_set_signals(int enable)
352 {
353 	int ret;
354 	if (signals_enabled == enable)
355 		return enable;
356 
357 	ret = signals_enabled;
358 	if (enable)
359 		unblock_signals();
360 	else block_signals();
361 
362 	return ret;
363 }
364 
um_set_signals_trace(int enable)365 int um_set_signals_trace(int enable)
366 {
367 	int ret;
368 	if (signals_enabled == enable)
369 		return enable;
370 
371 	ret = signals_enabled;
372 	if (enable)
373 		unblock_signals_trace();
374 	else
375 		block_signals_trace();
376 
377 	return ret;
378 }
379 
380 #ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT
mark_sigio_pending(void)381 void mark_sigio_pending(void)
382 {
383 	signals_pending |= SIGIO_MASK;
384 }
385 
block_signals_hard(void)386 void block_signals_hard(void)
387 {
388 	if (signals_blocked)
389 		return;
390 	signals_blocked = 1;
391 	barrier();
392 }
393 
unblock_signals_hard(void)394 void unblock_signals_hard(void)
395 {
396 	if (!signals_blocked)
397 		return;
398 	/* Must be set to 0 before we check the pending bits etc. */
399 	signals_blocked = 0;
400 	barrier();
401 
402 	if (signals_pending && signals_enabled) {
403 		/* this is a bit inefficient, but that's not really important */
404 		block_signals();
405 		unblock_signals();
406 	} else if (signals_pending & SIGIO_MASK) {
407 		/* we need to run time-travel handlers even if not enabled */
408 		sigio_run_timetravel_handlers();
409 	}
410 }
411 #endif
412 
os_is_signal_stack(void)413 int os_is_signal_stack(void)
414 {
415 	stack_t ss;
416 	sigaltstack(NULL, &ss);
417 
418 	return ss.ss_flags & SS_ONSTACK;
419 }
420