1*3c69bf01Sbluhm /* $OpenBSD: trapstack.c,v 1.2 2020/11/07 23:36:24 bluhm Exp $ */
28566a01bSbluhm /*
38566a01bSbluhm * Copyright (c) 2018 Todd Mortimer <mortimer@openbsd.org>
48566a01bSbluhm * Copyright (c) 2019 Alexander Bluhm <bluhm@openbsd.org>
58566a01bSbluhm *
68566a01bSbluhm * Permission to use, copy, modify, and distribute this software for any
78566a01bSbluhm * purpose with or without fee is hereby granted, provided that the above
88566a01bSbluhm * copyright notice and this permission notice appear in all copies.
98566a01bSbluhm *
108566a01bSbluhm * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
118566a01bSbluhm * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
128566a01bSbluhm * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
138566a01bSbluhm * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
148566a01bSbluhm * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
158566a01bSbluhm * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
168566a01bSbluhm * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
178566a01bSbluhm */
188566a01bSbluhm
198566a01bSbluhm #include <sys/mman.h>
208566a01bSbluhm
218566a01bSbluhm #include <err.h>
228566a01bSbluhm #include <stdlib.h>
238566a01bSbluhm #include <signal.h>
248566a01bSbluhm #include <unistd.h>
258566a01bSbluhm
268566a01bSbluhm #include "pivot.h"
278566a01bSbluhm
288566a01bSbluhm void handler(int);
298566a01bSbluhm void dotrap(void);
308566a01bSbluhm
31*3c69bf01Sbluhm static volatile char *trapmap;
328566a01bSbluhm
338566a01bSbluhm int
main(int argc,char * argv[])348566a01bSbluhm main(int argc, char *argv[])
358566a01bSbluhm {
368566a01bSbluhm stack_t ss;
378566a01bSbluhm struct sigaction act;
388566a01bSbluhm void (**newstack)(void);
398566a01bSbluhm long pagesize;
408566a01bSbluhm
418566a01bSbluhm ss.ss_sp = malloc(SIGSTKSZ);
428566a01bSbluhm if (ss.ss_sp == NULL)
438566a01bSbluhm err(1, "malloc sigstack");
448566a01bSbluhm ss.ss_size = SIGSTKSZ;
458566a01bSbluhm ss.ss_flags = 0;
468566a01bSbluhm if (sigaltstack(&ss, NULL) == -1)
478566a01bSbluhm err(1, "sigaltstack");
488566a01bSbluhm
498566a01bSbluhm act.sa_handler = handler;
508566a01bSbluhm sigemptyset(&act.sa_mask);
518566a01bSbluhm act.sa_flags = SA_ONSTACK;
528566a01bSbluhm
538566a01bSbluhm /* set up an alt stack on the heap that just calls dotrap */
548566a01bSbluhm pagesize = sysconf(_SC_PAGESIZE);
558566a01bSbluhm if (pagesize == -1)
568566a01bSbluhm err(1, "sysconf");
578566a01bSbluhm newstack = malloc(pagesize > SIGSTKSZ ? pagesize : SIGSTKSZ);
588566a01bSbluhm if (newstack == NULL)
598566a01bSbluhm err(1, "malloc newstack");
608566a01bSbluhm /* allow stack to change half a page up and down. */
618566a01bSbluhm newstack[pagesize/sizeof(*newstack)/2] = dotrap;
628566a01bSbluhm
63*3c69bf01Sbluhm trapmap = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_ANONYMOUS,
64*3c69bf01Sbluhm -1, 0);
65*3c69bf01Sbluhm if (trapmap == MAP_FAILED)
668566a01bSbluhm err(1, "mmap");
678566a01bSbluhm
688566a01bSbluhm if (sigaction(SIGSEGV, &act, NULL) == -1)
698566a01bSbluhm err(1, "sigaction");
708566a01bSbluhm pivot(&newstack[pagesize/sizeof(*newstack)/2]);
718566a01bSbluhm return 3;
728566a01bSbluhm }
738566a01bSbluhm
748566a01bSbluhm void
handler(int signum)758566a01bSbluhm handler(int signum)
768566a01bSbluhm {
778566a01bSbluhm _exit(0);
788566a01bSbluhm }
798566a01bSbluhm
808566a01bSbluhm void
dotrap(void)818566a01bSbluhm dotrap(void)
828566a01bSbluhm {
838566a01bSbluhm trapmap[0] = 'x';
848566a01bSbluhm exit(2);
858566a01bSbluhm }
86