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/* $OpenBSD: trapstack.c,v 1.2 2020/11/07 23:36:24 bluhm Exp $ */
/*
* Copyright (c) 2018 Todd Mortimer <mortimer@openbsd.org>
* Copyright (c) 2019 Alexander Bluhm <bluhm@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <sys/mman.h>
#include <err.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include "pivot.h"
void handler(int);
void dotrap(void);
static volatile char *trapmap;
int
main(int argc, char *argv[])
{
stack_t ss;
struct sigaction act;
void (**newstack)(void);
long pagesize;
ss.ss_sp = malloc(SIGSTKSZ);
if (ss.ss_sp == NULL)
err(1, "malloc sigstack");
ss.ss_size = SIGSTKSZ;
ss.ss_flags = 0;
if (sigaltstack(&ss, NULL) == -1)
err(1, "sigaltstack");
act.sa_handler = handler;
sigemptyset(&act.sa_mask);
act.sa_flags = SA_ONSTACK;
/* set up an alt stack on the heap that just calls dotrap */
pagesize = sysconf(_SC_PAGESIZE);
if (pagesize == -1)
err(1, "sysconf");
newstack = malloc(pagesize > SIGSTKSZ ? pagesize : SIGSTKSZ);
if (newstack == NULL)
err(1, "malloc newstack");
/* allow stack to change half a page up and down. */
newstack[pagesize/sizeof(*newstack)/2] = dotrap;
trapmap = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_ANONYMOUS,
-1, 0);
if (trapmap == MAP_FAILED)
err(1, "mmap");
if (sigaction(SIGSEGV, &act, NULL) == -1)
err(1, "sigaction");
pivot(&newstack[pagesize/sizeof(*newstack)/2]);
return 3;
}
void
handler(int signum)
{
_exit(0);
}
void
dotrap(void)
{
trapmap[0] = 'x';
exit(2);
}
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