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 26 void handler(int); 27 void doexit(void); 28 29 int 30 main(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 65 void 66 handler(int signum) 67 { 68 _exit(0); 69 } 70 71 void 72 doexit(void) 73 { 74 exit(2); 75 } 76