hurd/sigunwind.c

   1 /* longjmp cleanup function for unwinding past signal handlers.
   2    Copyright (C) 1995-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <hurd.h>
  20 #include <thread_state.h>
  21 #include <hurd/threadvar.h>
  22 #include <jmpbuf-unwind.h>
  23 #include <assert.h>
  24 #include <stdint.h>
  25 #include <pointer_guard.h>
  26
  27 /* _hurd_setup_sighandler puts a link on the `active resources' chain so that
  28    _longjmp_unwind will call this function with the `struct sigcontext *'
  29    describing the context interrupted by the signal, when `longjmp' is jumping
  30    to an environment that unwinds past the interrupted frame.  */
  31
  32 void
  33 _hurdsig_longjmp_from_handler (void *data, jmp_buf env, int val)
  34 {
  35   struct sigcontext *scp = data;
  36   struct hurd_sigstate *ss = _hurd_self_sigstate ();
  37   int onstack;
  38   inline void cleanup (void)
  39     {
  40       /* Destroy the MiG reply port used by the signal handler, and restore
  41          the reply port in use by the thread when interrupted.  */
  42       mach_port_t *reply_port = &__hurd_local_reply_port;
  43       if (*reply_port)
  44         {
  45           mach_port_t port = *reply_port;
  46           /* Assigning MACH_PORT_DEAD here tells libc's mig_get_reply_port
  47              not to get another reply port, but avoids mig_dealloc_reply_port
  48              trying to deallocate it after the receive fails (which it will,
  49              because the reply port will be bogus, regardless).  */
  50           *reply_port = MACH_PORT_DEAD;
  51           __mach_port_destroy (__mach_task_self (), port);
  52         }
  53       if (scp->sc_reply_port)
  54         __mach_port_destroy (__mach_task_self (), scp->sc_reply_port);
  55     }
  56
  57   __spin_lock (&ss->lock);
  58   /* We should only ever be called from _longjmp_unwind (in jmp-unwind.c),
  59      which calls us inside a critical section.  */
  60   assert (__spin_lock_locked (&ss->critical_section_lock));
  61   /* Are we on the alternate signal stack now?  */
  62   onstack = (ss->sigaltstack.ss_flags & SS_ONSTACK);
  63   __spin_unlock (&ss->lock);
  64
  65   if (onstack && ! scp->sc_onstack)
  66     {
  67       /* We are unwinding off the signal stack.  We must use sigreturn to
  68          do it robustly.  Mutate the sigcontext so that when sigreturn
  69          resumes from that context, it will be as if `__longjmp (ENV, VAL)'
  70          were done.  */
  71
  72       struct hurd_userlink *link;
  73
  74       inline uintptr_t demangle_ptr (uintptr_t x)
  75         {
  76           PTR_DEMANGLE (x);
  77           return x;
  78         }
  79
  80       /* Continue _longjmp_unwind's job of running the unwind
  81          forms for frames being unwound, since we will not
  82          return to its loop like this one, which called us.  */
  83       for (link = ss->active_resources;
  84            link && _JMPBUF_UNWINDS (env[0].__jmpbuf, link, demangle_ptr);
  85            link = link->thread.next)
  86         if (_hurd_userlink_unlink (link))
  87           {
  88             if (link->cleanup == &_hurdsig_longjmp_from_handler)
  89               {
  90                 /* We are unwinding past another signal handler invocation.
  91                    Just finish the cleanup for this (inner) one, and then
  92                    swap SCP to restore to the outer context.  */
  93                 cleanup ();
  94                 scp = link->cleanup_data;
  95               }
  96             else
  97               (*link->cleanup) (link->cleanup_data, env, val);
  98           }
  99
 100 #define sc_machine_thread_state paste(sc_,machine_thread_state)
 101 #define paste(a,b)      paste1(a,b)
 102 #define paste1(a,b)     a##b
 103
 104       /* There are no more unwind forms to be run!
 105          Now we can just have the sigreturn do the longjmp for us.  */
 106       _hurd_longjmp_thread_state
 107         ((struct machine_thread_state *) &scp->sc_machine_thread_state,
 108          env, val);
 109
 110       /* Restore to the same current signal mask.  If sigsetjmp saved the
 111          mask, longjmp has already restored it as desired; if not, we
 112          should leave it as it is.  */
 113       scp->sc_mask = ss->blocked;
 114
 115       /* sigreturn expects the link added by _hurd_setup_sighandler
 116          to still be there, but _longjmp_unwind removed it just before
 117          calling us.  Put it back now so sigreturn can find it.  */
 118       link = (void *) &scp[1];
 119       assert (! link->resource.next && ! link->resource.prevp);
 120       assert (link->thread.next == ss->active_resources);
 121       assert (link->thread.prevp == &ss->active_resources);
 122       if (link->thread.next)
 123         link->thread.next->thread.prevp = &link->thread.next;
 124       ss->active_resources = link;
 125
 126       /* We must momentarily exit the critical section so that sigreturn
 127          does not get upset with us.  But we don't want signal handlers
 128          running right now, because we are presently in the bogus state of
 129          having run all the unwind forms back to ENV's frame, but our SP is
 130          still inside those unwound frames.  */
 131       __spin_lock (&ss->lock);
 132       __spin_unlock (&ss->critical_section_lock);
 133       ss->blocked = ~(sigset_t) 0 & ~_SIG_CANT_MASK;
 134       __spin_unlock (&ss->lock);
 135
 136       /* Restore to the modified signal context that now
 137          performs `longjmp (ENV, VAL)'.  */
 138       __sigreturn (scp);
 139       assert (! "sigreturn returned!");
 140     }
 141
 142   /* We are not unwinding off the alternate signal stack.  So nothing
 143      really funny is going on here.  We can just clean up this handler
 144      frame and let _longjmp_unwind continue unwinding.  */
 145   cleanup ();
 146   ss->intr_port = scp->sc_intr_port;
 147 }