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Linux/arch/um/os-Linux/signal.c

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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 <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 
 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 
 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 
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 
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 
132 void deliver_alarm(void) {
133     timer_alarm_handler(SIGALRM, NULL, NULL);
134 }
135 
136 void timer_set_signal_handler(void)
137 {
138         set_handler(SIGALRM);
139 }
140 
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 
153 static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
154 {
155         uml_pm_wake();
156 }
157 
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 
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 
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 
251 void send_sigio_to_self(void)
252 {
253         kill(os_getpid(), SIGIO);
254 }
255 
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 
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 
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 
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 
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
381 void mark_sigio_pending(void)
382 {
383         signals_pending |= SIGIO_MASK;
384 }
385 
386 void block_signals_hard(void)
387 {
388         if (signals_blocked)
389                 return;
390         signals_blocked = 1;
391         barrier();
392 }
393 
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 
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 

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