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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 
 22 void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
 23         [SIGTRAP]       = relay_signal,
 24         [SIGFPE]        = relay_signal,
 25         [SIGILL]        = relay_signal,
 26         [SIGWINCH]      = winch,
 27         [SIGBUS]        = bus_handler,
 28         [SIGSEGV]       = segv_handler,
 29         [SIGIO]         = sigio_handler,
 30 };
 31 
 32 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
 33 {
 34         struct uml_pt_regs r;
 35         int save_errno = errno;
 36 
 37         r.is_user = 0;
 38         if (sig == SIGSEGV) {
 39                 /* For segfaults, we want the data from the sigcontext. */
 40                 get_regs_from_mc(&r, mc);
 41                 GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
 42         }
 43 
 44         /* enable signals if sig isn't IRQ signal */
 45         if ((sig != SIGIO) && (sig != SIGWINCH))
 46                 unblock_signals_trace();
 47 
 48         (*sig_info[sig])(sig, si, &r);
 49 
 50         errno = save_errno;
 51 }
 52 
 53 /*
 54  * These are the asynchronous signals.  SIGPROF is excluded because we want to
 55  * be able to profile all of UML, not just the non-critical sections.  If
 56  * profiling is not thread-safe, then that is not my problem.  We can disable
 57  * profiling when SMP is enabled in that case.
 58  */
 59 #define SIGIO_BIT 0
 60 #define SIGIO_MASK (1 << SIGIO_BIT)
 61 
 62 #define SIGALRM_BIT 1
 63 #define SIGALRM_MASK (1 << SIGALRM_BIT)
 64 
 65 static int signals_enabled;
 66 static unsigned int signals_pending;
 67 static unsigned int signals_active = 0;
 68 
 69 void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
 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_trace();
 80 
 81         sig_handler_common(sig, si, mc);
 82 
 83         set_signals_trace(enabled);
 84 }
 85 
 86 static void timer_real_alarm_handler(mcontext_t *mc)
 87 {
 88         struct uml_pt_regs regs;
 89 
 90         if (mc != NULL)
 91                 get_regs_from_mc(&regs, mc);
 92         else
 93                 memset(&regs, 0, sizeof(regs));
 94         timer_handler(SIGALRM, NULL, &regs);
 95 }
 96 
 97 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
 98 {
 99         int enabled;
100 
101         enabled = signals_enabled;
102         if (!signals_enabled) {
103                 signals_pending |= SIGALRM_MASK;
104                 return;
105         }
106 
107         block_signals_trace();
108 
109         signals_active |= SIGALRM_MASK;
110 
111         timer_real_alarm_handler(mc);
112 
113         signals_active &= ~SIGALRM_MASK;
114 
115         set_signals_trace(enabled);
116 }
117 
118 void deliver_alarm(void) {
119     timer_alarm_handler(SIGALRM, NULL, NULL);
120 }
121 
122 void timer_set_signal_handler(void)
123 {
124         set_handler(SIGALRM);
125 }
126 
127 void set_sigstack(void *sig_stack, int size)
128 {
129         stack_t stack = {
130                 .ss_flags = 0,
131                 .ss_sp = sig_stack,
132                 .ss_size = size
133         };
134 
135         if (sigaltstack(&stack, NULL) != 0)
136                 panic("enabling signal stack failed, errno = %d\n", errno);
137 }
138 
139 static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
140 {
141         uml_pm_wake();
142 }
143 
144 void register_pm_wake_signal(void)
145 {
146         set_handler(SIGUSR1);
147 }
148 
149 static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
150         [SIGSEGV] = sig_handler,
151         [SIGBUS] = sig_handler,
152         [SIGILL] = sig_handler,
153         [SIGFPE] = sig_handler,
154         [SIGTRAP] = sig_handler,
155 
156         [SIGIO] = sig_handler,
157         [SIGWINCH] = sig_handler,
158         [SIGALRM] = timer_alarm_handler,
159 
160         [SIGUSR1] = sigusr1_handler,
161 };
162 
163 static void hard_handler(int sig, siginfo_t *si, void *p)
164 {
165         ucontext_t *uc = p;
166         mcontext_t *mc = &uc->uc_mcontext;
167         unsigned long pending = 1UL << sig;
168 
169         do {
170                 int nested, bail;
171 
172                 /*
173                  * pending comes back with one bit set for each
174                  * interrupt that arrived while setting up the stack,
175                  * plus a bit for this interrupt, plus the zero bit is
176                  * set if this is a nested interrupt.
177                  * If bail is true, then we interrupted another
178                  * handler setting up the stack.  In this case, we
179                  * have to return, and the upper handler will deal
180                  * with this interrupt.
181                  */
182                 bail = to_irq_stack(&pending);
183                 if (bail)
184                         return;
185 
186                 nested = pending & 1;
187                 pending &= ~1;
188 
189                 while ((sig = ffs(pending)) != 0){
190                         sig--;
191                         pending &= ~(1 << sig);
192                         (*handlers[sig])(sig, (struct siginfo *)si, mc);
193                 }
194 
195                 /*
196                  * Again, pending comes back with a mask of signals
197                  * that arrived while tearing down the stack.  If this
198                  * is non-zero, we just go back, set up the stack
199                  * again, and handle the new interrupts.
200                  */
201                 if (!nested)
202                         pending = from_irq_stack(nested);
203         } while (pending);
204 }
205 
206 void set_handler(int sig)
207 {
208         struct sigaction action;
209         int flags = SA_SIGINFO | SA_ONSTACK;
210         sigset_t sig_mask;
211 
212         action.sa_sigaction = hard_handler;
213 
214         /* block irq ones */
215         sigemptyset(&action.sa_mask);
216         sigaddset(&action.sa_mask, SIGIO);
217         sigaddset(&action.sa_mask, SIGWINCH);
218         sigaddset(&action.sa_mask, SIGALRM);
219 
220         if (sig == SIGSEGV)
221                 flags |= SA_NODEFER;
222 
223         if (sigismember(&action.sa_mask, sig))
224                 flags |= SA_RESTART; /* if it's an irq signal */
225 
226         action.sa_flags = flags;
227         action.sa_restorer = NULL;
228         if (sigaction(sig, &action, NULL) < 0)
229                 panic("sigaction failed - errno = %d\n", errno);
230 
231         sigemptyset(&sig_mask);
232         sigaddset(&sig_mask, sig);
233         if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
234                 panic("sigprocmask failed - errno = %d\n", errno);
235 }
236 
237 void send_sigio_to_self(void)
238 {
239         kill(os_getpid(), SIGIO);
240 }
241 
242 int change_sig(int signal, int on)
243 {
244         sigset_t sigset;
245 
246         sigemptyset(&sigset);
247         sigaddset(&sigset, signal);
248         if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
249                 return -errno;
250 
251         return 0;
252 }
253 
254 void block_signals(void)
255 {
256         signals_enabled = 0;
257         /*
258          * This must return with signals disabled, so this barrier
259          * ensures that writes are flushed out before the return.
260          * This might matter if gcc figures out how to inline this and
261          * decides to shuffle this code into the caller.
262          */
263         barrier();
264 }
265 
266 void unblock_signals(void)
267 {
268         int save_pending;
269 
270         if (signals_enabled == 1)
271                 return;
272 
273         signals_enabled = 1;
274 #ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT
275         deliver_time_travel_irqs();
276 #endif
277 
278         /*
279          * We loop because the IRQ handler returns with interrupts off.  So,
280          * interrupts may have arrived and we need to re-enable them and
281          * recheck signals_pending.
282          */
283         while (1) {
284                 /*
285                  * Save and reset save_pending after enabling signals.  This
286                  * way, signals_pending won't be changed while we're reading it.
287                  *
288                  * Setting signals_enabled and reading signals_pending must
289                  * happen in this order, so have the barrier here.
290                  */
291                 barrier();
292 
293                 save_pending = signals_pending;
294                 if (save_pending == 0)
295                         return;
296 
297                 signals_pending = 0;
298 
299                 /*
300                  * We have pending interrupts, so disable signals, as the
301                  * handlers expect them off when they are called.  They will
302                  * be enabled again above. We need to trace this, as we're
303                  * expected to be enabling interrupts already, but any more
304                  * tracing that happens inside the handlers we call for the
305                  * pending signals will mess up the tracing state.
306                  */
307                 signals_enabled = 0;
308                 um_trace_signals_off();
309 
310                 /*
311                  * Deal with SIGIO first because the alarm handler might
312                  * schedule, leaving the pending SIGIO stranded until we come
313                  * back here.
314                  *
315                  * SIGIO's handler doesn't use siginfo or mcontext,
316                  * so they can be NULL.
317                  */
318                 if (save_pending & SIGIO_MASK)
319                         sig_handler_common(SIGIO, NULL, NULL);
320 
321                 /* Do not reenter the handler */
322 
323                 if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
324                         timer_real_alarm_handler(NULL);
325 
326                 /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
327 
328                 if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
329                         return;
330 
331                 /* Re-enable signals and trace that we're doing so. */
332                 um_trace_signals_on();
333                 signals_enabled = 1;
334         }
335 }
336 
337 int get_signals(void)
338 {
339         return signals_enabled;
340 }
341 
342 int set_signals(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();
351         else block_signals();
352 
353         return ret;
354 }
355 
356 int set_signals_trace(int enable)
357 {
358         int ret;
359         if (signals_enabled == enable)
360                 return enable;
361 
362         ret = signals_enabled;
363         if (enable)
364                 unblock_signals_trace();
365         else
366                 block_signals_trace();
367 
368         return ret;
369 }
370 
371 int os_is_signal_stack(void)
372 {
373         stack_t ss;
374         sigaltstack(NULL, &ss);
375 
376         return ss.ss_flags & SS_ONSTACK;
377 }
378 

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