arch/um/os-Linux/signal.c

   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 - sizeof(void *)
 133         };
 134
 135         if (sigaltstack(&stack, NULL) != 0)
 136                 panic("enabling signal stack failed, errno = %d\n", errno);
 137 }
 138
 139 static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
 140         [SIGSEGV] = sig_handler,
 141         [SIGBUS] = sig_handler,
 142         [SIGILL] = sig_handler,
 143         [SIGFPE] = sig_handler,
 144         [SIGTRAP] = sig_handler,
 145
 146         [SIGIO] = sig_handler,
 147         [SIGWINCH] = sig_handler,
 148         [SIGALRM] = timer_alarm_handler
 149 };
 150
 151 static void hard_handler(int sig, siginfo_t *si, void *p)
 152 {
 153         ucontext_t *uc = p;
 154         mcontext_t *mc = &uc->uc_mcontext;
 155         unsigned long pending = 1UL << sig;
 156
 157         do {
 158                 int nested, bail;
 159
 160                 /*
 161                  * pending comes back with one bit set for each
 162                  * interrupt that arrived while setting up the stack,
 163                  * plus a bit for this interrupt, plus the zero bit is
 164                  * set if this is a nested interrupt.
 165                  * If bail is true, then we interrupted another
 166                  * handler setting up the stack.  In this case, we
 167                  * have to return, and the upper handler will deal
 168                  * with this interrupt.
 169                  */
 170                 bail = to_irq_stack(&pending);
 171                 if (bail)
 172                         return;
 173
 174                 nested = pending & 1;
 175                 pending &= ~1;
 176
 177                 while ((sig = ffs(pending)) != 0){
 178                         sig--;
 179                         pending &= ~(1 << sig);
 180                         (*handlers[sig])(sig, (struct siginfo *)si, mc);
 181                 }
 182
 183                 /*
 184                  * Again, pending comes back with a mask of signals
 185                  * that arrived while tearing down the stack.  If this
 186                  * is non-zero, we just go back, set up the stack
 187                  * again, and handle the new interrupts.
 188                  */
 189                 if (!nested)
 190                         pending = from_irq_stack(nested);
 191         } while (pending);
 192 }
 193
 194 void set_handler(int sig)
 195 {
 196         struct sigaction action;
 197         int flags = SA_SIGINFO | SA_ONSTACK;
 198         sigset_t sig_mask;
 199
 200         action.sa_sigaction = hard_handler;
 201
 202         /* block irq ones */
 203         sigemptyset(&action.sa_mask);
 204         sigaddset(&action.sa_mask, SIGIO);
 205         sigaddset(&action.sa_mask, SIGWINCH);
 206         sigaddset(&action.sa_mask, SIGALRM);
 207
 208         if (sig == SIGSEGV)
 209                 flags |= SA_NODEFER;
 210
 211         if (sigismember(&action.sa_mask, sig))
 212                 flags |= SA_RESTART; /* if it's an irq signal */
 213
 214         action.sa_flags = flags;
 215         action.sa_restorer = NULL;
 216         if (sigaction(sig, &action, NULL) < 0)
 217                 panic("sigaction failed - errno = %d\n", errno);
 218
 219         sigemptyset(&sig_mask);
 220         sigaddset(&sig_mask, sig);
 221         if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
 222                 panic("sigprocmask failed - errno = %d\n", errno);
 223 }
 224
 225 int change_sig(int signal, int on)
 226 {
 227         sigset_t sigset;
 228
 229         sigemptyset(&sigset);
 230         sigaddset(&sigset, signal);
 231         if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
 232                 return -errno;
 233
 234         return 0;
 235 }
 236
 237 void block_signals(void)
 238 {
 239         signals_enabled = 0;
 240         /*
 241          * This must return with signals disabled, so this barrier
 242          * ensures that writes are flushed out before the return.
 243          * This might matter if gcc figures out how to inline this and
 244          * decides to shuffle this code into the caller.
 245          */
 246         barrier();
 247 }
 248
 249 void unblock_signals(void)
 250 {
 251         int save_pending;
 252
 253         if (signals_enabled == 1)
 254                 return;
 255
 256         signals_enabled = 1;
 257
 258         /*
 259          * We loop because the IRQ handler returns with interrupts off.  So,
 260          * interrupts may have arrived and we need to re-enable them and
 261          * recheck signals_pending.
 262          */
 263         while (1) {
 264                 /*
 265                  * Save and reset save_pending after enabling signals.  This
 266                  * way, signals_pending won't be changed while we're reading it.
 267                  *
 268                  * Setting signals_enabled and reading signals_pending must
 269                  * happen in this order, so have the barrier here.
 270                  */
 271                 barrier();
 272
 273                 save_pending = signals_pending;
 274                 if (save_pending == 0)
 275                         return;
 276
 277                 signals_pending = 0;
 278
 279                 /*
 280                  * We have pending interrupts, so disable signals, as the
 281                  * handlers expect them off when they are called.  They will
 282                  * be enabled again above. We need to trace this, as we're
 283                  * expected to be enabling interrupts already, but any more
 284                  * tracing that happens inside the handlers we call for the
 285                  * pending signals will mess up the tracing state.
 286                  */
 287                 signals_enabled = 0;
 288                 um_trace_signals_off();
 289
 290                 /*
 291                  * Deal with SIGIO first because the alarm handler might
 292                  * schedule, leaving the pending SIGIO stranded until we come
 293                  * back here.
 294                  *
 295                  * SIGIO's handler doesn't use siginfo or mcontext,
 296                  * so they can be NULL.
 297                  */
 298                 if (save_pending & SIGIO_MASK)
 299                         sig_handler_common(SIGIO, NULL, NULL);
 300
 301                 /* Do not reenter the handler */
 302
 303                 if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
 304                         timer_real_alarm_handler(NULL);
 305
 306                 /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
 307
 308                 if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
 309                         return;
 310
 311                 /* Re-enable signals and trace that we're doing so. */
 312                 um_trace_signals_on();
 313                 signals_enabled = 1;
 314         }
 315 }
 316
 317 int get_signals(void)
 318 {
 319         return signals_enabled;
 320 }
 321
 322 int set_signals(int enable)
 323 {
 324         int ret;
 325         if (signals_enabled == enable)
 326                 return enable;
 327
 328         ret = signals_enabled;
 329         if (enable)
 330                 unblock_signals();
 331         else block_signals();
 332
 333         return ret;
 334 }
 335
 336 int set_signals_trace(int enable)
 337 {
 338         int ret;
 339         if (signals_enabled == enable)
 340                 return enable;
 341
 342         ret = signals_enabled;
 343         if (enable)
 344                 unblock_signals_trace();
 345         else
 346                 block_signals_trace();
 347
 348         return ret;
 349 }
 350
 351 int os_is_signal_stack(void)
 352 {
 353         stack_t ss;
 354         sigaltstack(NULL, &ss);
 355
 356         return ss.ss_flags & SS_ONSTACK;
 357 }