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/* protsgix.c: PROTECTION (SIGNAL HANDLER) FOR POSIX
*
* $Id$
* Copyright (c) 2001-2020 Ravenbrook Limited. See end of file for license.
*
* This implements protection exception handling using POSIX signals.
* It is designed to run on any POSIX-compliant Unix.
*
*
* SOURCES
*
* .source.posix: POSIX specifications for signal.h and sigaction
* <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/signal.h.html>
* <https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigaction.html>
*
* .source.man: sigaction(2): FreeBSD System Calls Manual.
*
* .source.merge: A blend from primarily the FreeBSD version (protfri3.c)
* and the OSF/1 (DIGITAL UNIX) version (proto1.c); influenced by other
* Unix versions.
*/
#include "mpm.h"
#if !defined(MPS_OS_FR) && !defined(MPS_OS_LI)
#error "protsgix.c is specific to MPS_OS_FR or MPS_OS_LI"
#endif
#include "prmcix.h"
#include <errno.h> /* for errno */
#include <signal.h> /* for many functions */
#include <ucontext.h> /* for ucontext_t */
#include <unistd.h> /* for getpid */
SRCID(protsgix, "$Id$");
/* The previously-installed signal action, as returned by */
/* sigaction(3). See ProtSetup. */
static struct sigaction sigNext;
/* sigHandle -- protection signal handler
*
* This is the signal handler installed by ProtSetup to deal with
* protection faults. It is installed on the signal given by the
* PROT_SIGNAL macro (that is, SIGSEGV). It constructs a mutator
* context based on the signal context, and passes it to ArenaAccess,
* which attempts to handle the fault and remove its cause. If the
* fault is handled, then the handler returns and execution resumes.
* If it isn't handled, then sigHandle does its best to pass the
* signal on to the previously installed signal handler (sigNext);
* which it does by signalling itself using kill(2).
*
* .sigh.args: We set the SA_SIGINFO flag in the sa_flags field of the
* sigaction structure, and so the signal handler in the sa_sigaction
* field receives three arguments: signal number, pointer to signal
* info structure, pointer to signal context structure.
*
* .sigh.check: We check that info->si_code is SEGV_ACCERR (meaning
* "Invalid permissions for mapped object").
*
* .sign.addr: If so, we assume info->si_addr is the fault address.
*
* .sigh.mode: The fault type (read/write) does not appear to be
* available to the signal handler (see mail archive).
*/
#define PROT_SIGNAL SIGSEGV
static void sigHandle(int sig, siginfo_t *info, void *uap) /* .sigh.args */
{
ERRNO_SAVE {
int e;
/* sigset renamed to asigset due to clash with global on Darwin. */
sigset_t asigset, oldset;
struct sigaction sa;
AVER(sig == PROT_SIGNAL);
if (info->si_code == SEGV_ACCERR) { /* .sigh.check */
AccessSet mode;
Addr base;
MutatorContextStruct context;
MutatorContextInitFault(&context, info, (ucontext_t *)uap);
mode = AccessREAD | AccessWRITE; /* .sigh.mode */
/* We assume that the access is for one word at the address. */
base = (Addr)info->si_addr; /* .sigh.addr */
/* Offer each protection structure the opportunity to handle the */
/* exception. If it succeeds, then allow the mutator to continue. */
if (ArenaAccess(base, mode, &context))
goto done;
}
/* The exception was not handled by any known protection structure, */
/* so throw it to the previously installed handler. That handler won't */
/* get an accurate context (the MPS would fail if it were the second in */
/* line) but it's the best we can do. */
e = sigemptyset(&asigset);
AVER(e == 0);
e = sigaddset(&asigset, PROT_SIGNAL);
AVER(e == 0);
/* FIX: We look at the old signal structure and call the handler if */
/* we understand it. Note: We unblock the signal when calling the */
/* handler to allow some form of reentrancy (e.g. if the handler */
/* accesses memory by the MPS, it the code above will be called. */
/* This is, of course, not necessarily a good idea, but allows some */
/* form of last-resort handling at least. */
if (sigNext.sa_flags & SA_SIGINFO) {
/* Extended signal handler. */
e = sigprocmask(SIG_UNBLOCK, &asigset, &oldset);
AVER(e == 0);
(*sigNext.sa_sigaction)(sig, info, uap);
e = sigprocmask(SIG_SETMASK, &oldset, NULL);
AVER(e == 0);
} else if (sigNext.sa_handler == SIG_DFL || sigNext.sa_handler == SIG_IGN) {
/* Use default mechanisms. */
e = sigaction(PROT_SIGNAL, &sigNext, &sa);
AVER(e == 0);
e = sigprocmask(SIG_UNBLOCK, &asigset, &oldset);
AVER(e == 0);
e = kill(getpid(), PROT_SIGNAL);
AVER(e == 0);
e = sigprocmask(SIG_SETMASK, &oldset, NULL);
AVER(e == 0);
e = sigaction(PROT_SIGNAL, &sa, NULL);
AVER(e == 0);
} else {
/* Simple signal handler. */
e = sigprocmask(SIG_UNBLOCK, &asigset, &oldset);
AVER(e == 0);
(*sigNext.sa_handler)(sig);
e = sigprocmask(SIG_SETMASK, &oldset, NULL);
AVER(e == 0);
}
done:
;
} ERRNO_RESTORE;
}
/* ProtSetup -- global protection setup
*
* Under Unix, the global setup involves installing a signal handler
* on PROT_SIGNAL to catch and handle page faults (see sigHandle).
* The previous handler is recorded so that it can be reached from
* sigHandle if it fails to handle the fault.
*
* NOTE: There are problems with this approach:
* 1. we can't honor the sa_flags for the previous handler,
* 2. what if this thread is suspended just after calling signal(3)?
* The sigNext variable will never be initialized!
*/
void ProtSetup(void)
{
struct sigaction sa;
int result;
sa.sa_sigaction = sigHandle;
result = sigemptyset(&sa.sa_mask);
AVER(result == 0);
sa.sa_flags = SA_SIGINFO | SA_RESTART;
result = sigaction(PROT_SIGNAL, &sa, &sigNext);
AVER(result == 0);
}
/* C. COPYRIGHT AND LICENSE
*
* Copyright (C) 2001-2020 Ravenbrook Limited <https://www.ravenbrook.com/>.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
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