arch/um/os-Linux/signal.c

   1 /*
   2  * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
   3  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
   4  * Copyright (C) 2004 PathScale, Inc
   5  * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   6  * Licensed under the GPL
   7  */
   8
   9 #include <stdlib.h>
  10 #include <stdarg.h>
  11 #include <errno.h>
  12 #include <signal.h>
  13 #include <strings.h>
  14 #include <as-layout.h>
  15 #include <kern_util.h>
  16 #include <os.h>
  17 #include <sysdep/mcontext.h>
  18 #include <um_malloc.h>
  19
  20 void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
  21         [SIGTRAP]       = relay_signal,
  22         [SIGFPE]        = relay_signal,
  23         [SIGILL]        = relay_signal,
  24         [SIGWINCH]      = winch,
  25         [SIGBUS]        = bus_handler,
  26         [SIGSEGV]       = segv_handler,
  27         [SIGIO]         = sigio_handler,
  28         [SIGALRM]       = timer_handler
  29 };
  30
  31 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
  32 {
  33         struct uml_pt_regs *r;
  34         int save_errno = errno;
  35
  36         r = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
  37         if (!r)
  38                 panic("out of memory");
  39
  40         r->is_user = 0;
  41         if (sig == SIGSEGV) {
  42                 /* For segfaults, we want the data from the sigcontext. */
  43                 get_regs_from_mc(r, mc);
  44                 GET_FAULTINFO_FROM_MC(r->faultinfo, mc);
  45         }
  46
  47         /* enable signals if sig isn't IRQ signal */
  48         if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
  49                 unblock_signals();
  50
  51         (*sig_info[sig])(sig, si, r);
  52
  53         errno = save_errno;
  54
  55         free(r);
  56 }
  57
  58 /*
  59  * These are the asynchronous signals.  SIGPROF is excluded because we want to
  60  * be able to profile all of UML, not just the non-critical sections.  If
  61  * profiling is not thread-safe, then that is not my problem.  We can disable
  62  * profiling when SMP is enabled in that case.
  63  */
  64 #define SIGIO_BIT 0
  65 #define SIGIO_MASK (1 << SIGIO_BIT)
  66
  67 #define SIGALRM_BIT 1
  68 #define SIGALRM_MASK (1 << SIGALRM_BIT)
  69
  70 static int signals_enabled;
  71 static unsigned int signals_pending;
  72 static unsigned int signals_active = 0;
  73
  74 void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
  75 {
  76         int enabled;
  77
  78         enabled = signals_enabled;
  79         if (!enabled && (sig == SIGIO)) {
  80                 signals_pending |= SIGIO_MASK;
  81                 return;
  82         }
  83
  84         block_signals();
  85
  86         sig_handler_common(sig, si, mc);
  87
  88         set_signals(enabled);
  89 }
  90
  91 static void timer_real_alarm_handler(mcontext_t *mc)
  92 {
  93         struct uml_pt_regs *regs;
  94
  95         regs = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
  96         if (!regs)
  97                 panic("out of memory");
  98
  99         if (mc != NULL)
 100                 get_regs_from_mc(regs, mc);
 101         timer_handler(SIGALRM, NULL, regs);
 102
 103         free(regs);
 104 }
 105
 106 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
 107 {
 108         int enabled;
 109
 110         enabled = signals_enabled;
 111         if (!signals_enabled) {
 112                 signals_pending |= SIGALRM_MASK;
 113                 return;
 114         }
 115
 116         block_signals();
 117
 118         signals_active |= SIGALRM_MASK;
 119
 120         timer_real_alarm_handler(mc);
 121
 122         signals_active &= ~SIGALRM_MASK;
 123
 124         set_signals(enabled);
 125 }
 126
 127 void deliver_alarm(void) {
 128     timer_alarm_handler(SIGALRM, NULL, NULL);
 129 }
 130
 131 void timer_set_signal_handler(void)
 132 {
 133         set_handler(SIGALRM);
 134 }
 135
 136 void set_sigstack(void *sig_stack, int size)
 137 {
 138         stack_t stack = {
 139                 .ss_flags = 0,
 140                 .ss_sp = sig_stack,
 141                 .ss_size = size - sizeof(void *)
 142         };
 143
 144         if (sigaltstack(&stack, NULL) != 0)
 145                 panic("enabling signal stack failed, errno = %d\n", errno);
 146 }
 147
 148 static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
 149         [SIGSEGV] = sig_handler,
 150         [SIGBUS] = sig_handler,
 151         [SIGILL] = sig_handler,
 152         [SIGFPE] = sig_handler,
 153         [SIGTRAP] = sig_handler,
 154
 155         [SIGIO] = sig_handler,
 156         [SIGWINCH] = sig_handler,
 157         [SIGALRM] = timer_alarm_handler
 158 };
 159
 160 static void hard_handler(int sig, siginfo_t *si, void *p)
 161 {
 162         struct ucontext *uc = p;
 163         mcontext_t *mc = &uc->uc_mcontext;
 164         unsigned long pending = 1UL << sig;
 165
 166         do {
 167                 int nested, bail;
 168
 169                 /*
 170                  * pending comes back with one bit set for each
 171                  * interrupt that arrived while setting up the stack,
 172                  * plus a bit for this interrupt, plus the zero bit is
 173                  * set if this is a nested interrupt.
 174                  * If bail is true, then we interrupted another
 175                  * handler setting up the stack.  In this case, we
 176                  * have to return, and the upper handler will deal
 177                  * with this interrupt.
 178                  */
 179                 bail = to_irq_stack(&pending);
 180                 if (bail)
 181                         return;
 182
 183                 nested = pending & 1;
 184                 pending &= ~1;
 185
 186                 while ((sig = ffs(pending)) != 0){
 187                         sig--;
 188                         pending &= ~(1 << sig);
 189                         (*handlers[sig])(sig, (struct siginfo *)si, mc);
 190                 }
 191
 192                 /*
 193                  * Again, pending comes back with a mask of signals
 194                  * that arrived while tearing down the stack.  If this
 195                  * is non-zero, we just go back, set up the stack
 196                  * again, and handle the new interrupts.
 197                  */
 198                 if (!nested)
 199                         pending = from_irq_stack(nested);
 200         } while (pending);
 201 }
 202
 203 void set_handler(int sig)
 204 {
 205         struct sigaction action;
 206         int flags = SA_SIGINFO | SA_ONSTACK;
 207         sigset_t sig_mask;
 208
 209         action.sa_sigaction = hard_handler;
 210
 211         /* block irq ones */
 212         sigemptyset(&action.sa_mask);
 213         sigaddset(&action.sa_mask, SIGIO);
 214         sigaddset(&action.sa_mask, SIGWINCH);
 215         sigaddset(&action.sa_mask, SIGALRM);
 216
 217         if (sig == SIGSEGV)
 218                 flags |= SA_NODEFER;
 219
 220         if (sigismember(&action.sa_mask, sig))
 221                 flags |= SA_RESTART; /* if it's an irq signal */
 222
 223         action.sa_flags = flags;
 224         action.sa_restorer = NULL;
 225         if (sigaction(sig, &action, NULL) < 0)
 226                 panic("sigaction failed - errno = %d\n", errno);
 227
 228         sigemptyset(&sig_mask);
 229         sigaddset(&sig_mask, sig);
 230         if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
 231                 panic("sigprocmask failed - errno = %d\n", errno);
 232 }
 233
 234 int change_sig(int signal, int on)
 235 {
 236         sigset_t sigset;
 237
 238         sigemptyset(&sigset);
 239         sigaddset(&sigset, signal);
 240         if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
 241                 return -errno;
 242
 243         return 0;
 244 }
 245
 246 void block_signals(void)
 247 {
 248         signals_enabled = 0;
 249         /*
 250          * This must return with signals disabled, so this barrier
 251          * ensures that writes are flushed out before the return.
 252          * This might matter if gcc figures out how to inline this and
 253          * decides to shuffle this code into the caller.
 254          */
 255         barrier();
 256 }
 257
 258 void unblock_signals(void)
 259 {
 260         int save_pending;
 261
 262         if (signals_enabled == 1)
 263                 return;
 264
 265         /*
 266          * We loop because the IRQ handler returns with interrupts off.  So,
 267          * interrupts may have arrived and we need to re-enable them and
 268          * recheck signals_pending.
 269          */
 270         while (1) {
 271                 /*
 272                  * Save and reset save_pending after enabling signals.  This
 273                  * way, signals_pending won't be changed while we're reading it.
 274                  */
 275                 signals_enabled = 1;
 276
 277                 /*
 278                  * Setting signals_enabled and reading signals_pending must
 279                  * happen in this order.
 280                  */
 281                 barrier();
 282
 283                 save_pending = signals_pending;
 284                 if (save_pending == 0)
 285                         return;
 286
 287                 signals_pending = 0;
 288
 289                 /*
 290                  * We have pending interrupts, so disable signals, as the
 291                  * handlers expect them off when they are called.  They will
 292                  * be enabled again above.
 293                  */
 294
 295                 signals_enabled = 0;
 296
 297                 /*
 298                  * Deal with SIGIO first because the alarm handler might
 299                  * schedule, leaving the pending SIGIO stranded until we come
 300                  * back here.
 301                  *
 302                  * SIGIO's handler doesn't use siginfo or mcontext,
 303                  * so they can be NULL.
 304                  */
 305                 if (save_pending & SIGIO_MASK)
 306                         sig_handler_common(SIGIO, NULL, NULL);
 307
 308                 /* Do not reenter the handler */
 309
 310                 if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
 311                         timer_real_alarm_handler(NULL);
 312
 313                 /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
 314
 315                 if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
 316                         return;
 317
 318         }
 319 }
 320
 321 int get_signals(void)
 322 {
 323         return signals_enabled;
 324 }
 325
 326 int set_signals(int enable)
 327 {
 328         int ret;
 329         if (signals_enabled == enable)
 330                 return enable;
 331
 332         ret = signals_enabled;
 333         if (enable)
 334                 unblock_signals();
 335         else block_signals();
 336
 337         return ret;
 338 }
 339
 340 int os_is_signal_stack(void)
 341 {
 342         stack_t ss;
 343         sigaltstack(NULL, &ss);
 344
 345         return ss.ss_flags & SS_ONSTACK;
 346 }