1/*	$OpenBSD: callstack.c,v 1.1 2019/09/23 08:34:07 bluhm Exp $	*/
2/*
3 * Copyright (c) 2018 Todd Mortimer <mortimer@openbsd.org>
4 * Copyright (c) 2019 Alexander Bluhm <bluhm@openbsd.org>
5 *
6 * Permission to use, copy, modify, and distribute this software for any
7 * purpose with or without fee is hereby granted, provided that the above
8 * copyright notice and this permission notice appear in all copies.
9 *
10 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
11 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
13 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17 */
18
19#include <err.h>
20#include <stdlib.h>
21#include <signal.h>
22#include <unistd.h>
23
24#include "pivot.h"
25
26void handler(int);
27void doexit(void);
28
29int
30main(int argc, char *argv[])
31{
32	stack_t ss;
33	struct sigaction act;
34	void (**newstack)(void);
35	long pagesize;
36
37	ss.ss_sp = malloc(SIGSTKSZ);
38	if (ss.ss_sp == NULL)
39		err(1, "malloc sigstack");
40	ss.ss_size = SIGSTKSZ;
41	ss.ss_flags = 0;
42	if (sigaltstack(&ss, NULL) == -1)
43		err(1, "sigaltstack");
44
45	act.sa_handler = handler;
46	sigemptyset(&act.sa_mask);
47	act.sa_flags = SA_ONSTACK;
48
49	/* set up an alt stack on the heap that just calls doexit */
50	pagesize = sysconf(_SC_PAGESIZE);
51	if (pagesize == -1)
52		err(1, "sysconf");
53	newstack = malloc(pagesize > SIGSTKSZ ? pagesize : SIGSTKSZ);
54	if (newstack == NULL)
55		err(1, "malloc newstack");
56	/* allow stack to change half a page up and down. */
57	newstack[pagesize/sizeof(*newstack)/2] = doexit;
58
59	if (sigaction(SIGSEGV, &act, NULL) == -1)
60		err(1, "sigaction");
61	pivot(&newstack[pagesize/sizeof(*newstack)/2]);
62	return 3;
63}
64
65void
66handler(int signum)
67{
68	_exit(0);
69}
70
71void
72doexit(void)
73{
74	exit(2);
75}
76