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 #include <sys/ucontext.h>
  20
  21 void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
  22         [SIGTRAP]       = relay_signal,
  23         [SIGFPE]        = relay_signal,
  24         [SIGILL]        = relay_signal,
  25         [SIGWINCH]      = winch,
  26         [SIGBUS]        = bus_handler,
  27         [SIGSEGV]       = segv_handler,
  28         [SIGIO]         = sigio_handler,
  29         [SIGALRM]       = timer_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 = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
  38         if (!r)
  39                 panic("out of memory");
  40
  41         r->is_user = 0;
  42         if (sig == SIGSEGV) {
  43                 /* For segfaults, we want the data from the sigcontext. */
  44                 get_regs_from_mc(r, mc);
  45                 GET_FAULTINFO_FROM_MC(r->faultinfo, mc);
  46         }
  47
  48         /* enable signals if sig isn't IRQ signal */
  49         if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
  50                 unblock_signals();
  51
  52         (*sig_info[sig])(sig, si, r);
  53
  54         errno = save_errno;
  55
  56         free(r);
  57 }
  58
  59 /*
  60  * These are the asynchronous signals.  SIGPROF is excluded because we want to
  61  * be able to profile all of UML, not just the non-critical sections.  If
  62  * profiling is not thread-safe, then that is not my problem.  We can disable
  63  * profiling when SMP is enabled in that case.
  64  */
  65 #define SIGIO_BIT 0
  66 #define SIGIO_MASK (1 << SIGIO_BIT)
  67
  68 #define SIGALRM_BIT 1
  69 #define SIGALRM_MASK (1 << SIGALRM_BIT)
  70
  71 static int signals_enabled;
  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;
  78
  79         enabled = signals_enabled;
  80         if (!enabled && (sig == SIGIO)) {
  81                 signals_pending |= SIGIO_MASK;
  82                 return;
  83         }
  84
  85         block_signals();
  86
  87         sig_handler_common(sig, si, mc);
  88
  89         set_signals(enabled);
  90 }
  91
  92 static void timer_real_alarm_handler(mcontext_t *mc)
  93 {
  94         struct uml_pt_regs *regs;
  95
  96         regs = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
  97         if (!regs)
  98                 panic("out of memory");
  99
 100         if (mc != NULL)
 101                 get_regs_from_mc(regs, mc);
 102         timer_handler(SIGALRM, NULL, regs);
 103
 104         free(regs);
 105 }
 106
 107 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
 108 {
 109         int enabled;
 110
 111         enabled = signals_enabled;
 112         if (!signals_enabled) {
 113                 signals_pending |= SIGALRM_MASK;
 114                 return;
 115         }
 116
 117         block_signals();
 118
 119         signals_active |= SIGALRM_MASK;
 120
 121         timer_real_alarm_handler(mc);
 122
 123         signals_active &= ~SIGALRM_MASK;
 124
 125         set_signals(enabled);
 126 }
 127
 128 void deliver_alarm(void) {
 129     timer_alarm_handler(SIGALRM, NULL, NULL);
 130 }
 131
 132 void timer_set_signal_handler(void)
 133 {
 134         set_handler(SIGALRM);
 135 }
 136
 137 void set_sigstack(void *sig_stack, int size)
 138 {
 139         stack_t stack = {
 140                 .ss_flags = 0,
 141                 .ss_sp = sig_stack,
 142                 .ss_size = size - sizeof(void *)
 143         };
 144
 145         if (sigaltstack(&stack, NULL) != 0)
 146                 panic("enabling signal stack failed, errno = %d\n", errno);
 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
 161 static void hard_handler(int sig, siginfo_t *si, void *p)
 162 {
 163         ucontext_t *uc = p;
 164         mcontext_t *mc = &uc->uc_mcontext;
 165         unsigned long pending = 1UL << sig;
 166
 167         do {
 168                 int nested, bail;
 169
 170                 /*
 171                  * pending comes back with one bit set for each
 172                  * interrupt that arrived while setting up the stack,
 173                  * plus a bit for this interrupt, plus the zero bit is
 174                  * set if this is a nested interrupt.
 175                  * If bail is true, then we interrupted another
 176                  * handler setting up the stack.  In this case, we
 177                  * have to return, and the upper handler will deal
 178                  * with this interrupt.
 179                  */
 180                 bail = to_irq_stack(&pending);
 181                 if (bail)
 182                         return;
 183
 184                 nested = pending & 1;
 185                 pending &= ~1;
 186
 187                 while ((sig = ffs(pending)) != 0){
 188                         sig--;
 189                         pending &= ~(1 << sig);
 190                         (*handlers[sig])(sig, (struct siginfo *)si, mc);
 191                 }
 192
 193                 /*
 194                  * Again, pending comes back with a mask of signals
 195                  * that arrived while tearing down the stack.  If this
 196                  * is non-zero, we just go back, set up the stack
 197                  * again, and handle the new interrupts.
 198                  */
 199                 if (!nested)
 200                         pending = from_irq_stack(nested);
 201         } while (pending);
 202 }
 203
 204 void set_handler(int sig)
 205 {
 206         struct sigaction action;
 207         int flags = SA_SIGINFO | SA_ONSTACK;
 208         sigset_t sig_mask;
 209
 210         action.sa_sigaction = hard_handler;
 211
 212         /* block irq ones */
 213         sigemptyset(&action.sa_mask);
 214         sigaddset(&action.sa_mask, SIGIO);
 215         sigaddset(&action.sa_mask, SIGWINCH);
 216         sigaddset(&action.sa_mask, SIGALRM);
 217
 218         if (sig == SIGSEGV)
 219                 flags |= SA_NODEFER;
 220
 221         if (sigismember(&action.sa_mask, sig))
 222                 flags |= SA_RESTART; /* if it's an irq signal */
 223
 224         action.sa_flags = flags;
 225         action.sa_restorer = NULL;
 226         if (sigaction(sig, &action, NULL) < 0)
 227                 panic("sigaction failed - errno = %d\n", errno);
 228
 229         sigemptyset(&sig_mask);
 230         sigaddset(&sig_mask, sig);
 231         if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
 232                 panic("sigprocmask failed - errno = %d\n", errno);
 233 }
 234
 235 int change_sig(int signal, int on)
 236 {
 237         sigset_t sigset;
 238
 239         sigemptyset(&sigset);
 240         sigaddset(&sigset, signal);
 241         if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
 242                 return -errno;
 243
 244         return 0;
 245 }
 246
 247 void block_signals(void)
 248 {
 249         signals_enabled = 0;
 250         /*
 251          * This must return with signals disabled, so this barrier
 252          * ensures that writes are flushed out before the return.
 253          * This might matter if gcc figures out how to inline this and
 254          * decides to shuffle this code into the caller.
 255          */
 256         barrier();
 257 }
 258
 259 void unblock_signals(void)
 260 {
 261         int save_pending;
 262
 263         if (signals_enabled == 1)
 264                 return;
 265
 266         /*
 267          * We loop because the IRQ handler returns with interrupts off.  So,
 268          * interrupts may have arrived and we need to re-enable them and
 269          * recheck signals_pending.
 270          */
 271         while (1) {
 272                 /*
 273                  * Save and reset save_pending after enabling signals.  This
 274                  * way, signals_pending won't be changed while we're reading it.
 275                  */
 276                 signals_enabled = 1;
 277
 278                 /*
 279                  * Setting signals_enabled and reading signals_pending must
 280                  * happen in this order.
 281                  */
 282                 barrier();
 283
 284                 save_pending = signals_pending;
 285                 if (save_pending == 0)
 286                         return;
 287
 288                 signals_pending = 0;
 289
 290                 /*
 291                  * We have pending interrupts, so disable signals, as the
 292                  * handlers expect them off when they are called.  They will
 293                  * be enabled again above.
 294                  */
 295
 296                 signals_enabled = 0;
 297
 298                 /*
 299                  * Deal with SIGIO first because the alarm handler might
 300                  * schedule, leaving the pending SIGIO stranded until we come
 301                  * back here.
 302                  *
 303                  * SIGIO's handler doesn't use siginfo or mcontext,
 304                  * so they can be NULL.
 305                  */
 306                 if (save_pending & SIGIO_MASK)
 307                         sig_handler_common(SIGIO, NULL, NULL);
 308
 309                 /* Do not reenter the handler */
 310
 311                 if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
 312                         timer_real_alarm_handler(NULL);
 313
 314                 /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
 315
 316                 if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
 317                         return;
 318
 319         }
 320 }
 321
 322 int get_signals(void)
 323 {
 324         return signals_enabled;
 325 }
 326
 327 int set_signals(int enable)
 328 {
 329         int ret;
 330         if (signals_enabled == enable)
 331                 return enable;
 332
 333         ret = signals_enabled;
 334         if (enable)
 335                 unblock_signals();
 336         else block_signals();
 337
 338         return ret;
 339 }
 340
 341 int os_is_signal_stack(void)
 342 {
 343         stack_t ss;
 344         sigaltstack(NULL, &ss);
 345
 346         return ss.ss_flags & SS_ONSTACK;
 347 }