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
23void (*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
33static 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
66int signals_enabled;
67#ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT
68static int signals_blocked;
69#else
70#define signals_blocked 0
71#endif
72static unsigned int signals_pending;
73static unsigned int signals_active = 0;
74
75void 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
100static 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
111void 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
132void deliver_alarm(void) {
133    timer_alarm_handler(SIGALRM, NULL, NULL);
134}
135
136void timer_set_signal_handler(void)
137{
138	set_handler(SIGALRM);
139}
140
141void 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
153static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
154{
155	uml_pm_wake();
156}
157
158void register_pm_wake_signal(void)
159{
160	set_handler(SIGUSR1);
161}
162
163static 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
177static 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
220void 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
251void send_sigio_to_self(void)
252{
253	kill(os_getpid(), SIGIO);
254}
255
256int 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
268void 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
280void 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
351int 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
365int 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
381void mark_sigio_pending(void)
382{
383	signals_pending |= SIGIO_MASK;
384}
385
386void block_signals_hard(void)
387{
388	if (signals_blocked)
389		return;
390	signals_blocked = 1;
391	barrier();
392}
393
394void 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
413int os_is_signal_stack(void)
414{
415	stack_t ss;
416	sigaltstack(NULL, &ss);
417
418	return ss.ss_flags & SS_ONSTACK;
419}
420