1/*
  2 * Stas Sergeev <stsp@users.sourceforge.net>
  3 *
  4 * test sigaltstack(SS_ONSTACK | SS_AUTODISARM)
  5 * If that succeeds, then swapcontext() can be used inside sighandler safely.
  6 *
  7 */
  8
  9#define _GNU_SOURCE
 10#include <signal.h>
 11#include <stdio.h>
 12#include <stdlib.h>
 13#include <sys/mman.h>
 14#include <ucontext.h>
 15#include <alloca.h>
 16#include <string.h>
 17#include <assert.h>
 18#include <errno.h>
 19
 20#ifndef SS_AUTODISARM
 21#define SS_AUTODISARM  (1U << 31)
 22#endif
 23
 24static void *sstack, *ustack;
 25static ucontext_t uc, sc;
 26static const char *msg = "[OK]\tStack preserved";
 27static const char *msg2 = "[FAIL]\tStack corrupted";
 28struct stk_data {
 29	char msg[128];
 30	int flag;
 31};
 32
 33void my_usr1(int sig, siginfo_t *si, void *u)
 34{
 35	char *aa;
 36	int err;
 37	stack_t stk;
 38	struct stk_data *p;
 39
 40	register unsigned long sp asm("sp");
 41
 42	if (sp < (unsigned long)sstack ||
 43			sp >= (unsigned long)sstack + SIGSTKSZ) {
 44		printf("[FAIL]\tSP is not on sigaltstack\n");
 45		exit(EXIT_FAILURE);
 46	}
 47	/* put some data on stack. other sighandler will try to overwrite it */
 48	aa = alloca(1024);
 49	assert(aa);
 50	p = (struct stk_data *)(aa + 512);
 51	strcpy(p->msg, msg);
 52	p->flag = 1;
 53	printf("[RUN]\tsignal USR1\n");
 54	err = sigaltstack(NULL, &stk);
 55	if (err) {
 56		perror("[FAIL]\tsigaltstack()");
 57		exit(EXIT_FAILURE);
 58	}
 59	if (stk.ss_flags != SS_DISABLE)
 60		printf("[FAIL]\tss_flags=%i, should be SS_DISABLE\n",
 61				stk.ss_flags);
 62	else
 63		printf("[OK]\tsigaltstack is disabled in sighandler\n");
 64	swapcontext(&sc, &uc);
 65	printf("%s\n", p->msg);
 66	if (!p->flag) {
 67		printf("[RUN]\tAborting\n");
 68		exit(EXIT_FAILURE);
 69	}
 70}
 71
 72void my_usr2(int sig, siginfo_t *si, void *u)
 73{
 74	char *aa;
 75	struct stk_data *p;
 76
 77	printf("[RUN]\tsignal USR2\n");
 78	aa = alloca(1024);
 79	/* dont run valgrind on this */
 80	/* try to find the data stored by previous sighandler */
 81	p = memmem(aa, 1024, msg, strlen(msg));
 82	if (p) {
 83		printf("[FAIL]\tsigaltstack re-used\n");
 84		/* corrupt the data */
 85		strcpy(p->msg, msg2);
 86		/* tell other sighandler that his data is corrupted */
 87		p->flag = 0;
 88	}
 89}
 90
 91static void switch_fn(void)
 92{
 93	printf("[RUN]\tswitched to user ctx\n");
 94	raise(SIGUSR2);
 95	setcontext(&sc);
 96}
 97
 98int main(void)
 99{
100	struct sigaction act;
101	stack_t stk;
102	int err;
103
104	sigemptyset(&act.sa_mask);
105	act.sa_flags = SA_ONSTACK | SA_SIGINFO;
106	act.sa_sigaction = my_usr1;
107	sigaction(SIGUSR1, &act, NULL);
108	act.sa_sigaction = my_usr2;
109	sigaction(SIGUSR2, &act, NULL);
110	sstack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
111		      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
112	if (sstack == MAP_FAILED) {
113		perror("mmap()");
114		return EXIT_FAILURE;
115	}
116
117	err = sigaltstack(NULL, &stk);
118	if (err) {
119		perror("[FAIL]\tsigaltstack()");
120		exit(EXIT_FAILURE);
121	}
122	if (stk.ss_flags == SS_DISABLE) {
123		printf("[OK]\tInitial sigaltstack state was SS_DISABLE\n");
124	} else {
125		printf("[FAIL]\tInitial sigaltstack state was %i; should have been SS_DISABLE\n", stk.ss_flags);
126		return EXIT_FAILURE;
127	}
128
129	stk.ss_sp = sstack;
130	stk.ss_size = SIGSTKSZ;
131	stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
132	err = sigaltstack(&stk, NULL);
133	if (err) {
134		if (errno == EINVAL) {
135			printf("[NOTE]\tThe running kernel doesn't support SS_AUTODISARM\n");
136			/*
137			 * If test cases for the !SS_AUTODISARM variant were
138			 * added, we could still run them.  We don't have any
139			 * test cases like that yet, so just exit and report
140			 * success.
141			 */
142			return 0;
143		} else {
144			perror("[FAIL]\tsigaltstack(SS_ONSTACK | SS_AUTODISARM)");
145			return EXIT_FAILURE;
146		}
147	}
148
149	ustack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
150		      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
151	if (ustack == MAP_FAILED) {
152		perror("mmap()");
153		return EXIT_FAILURE;
154	}
155	getcontext(&uc);
156	uc.uc_link = NULL;
157	uc.uc_stack.ss_sp = ustack;
158	uc.uc_stack.ss_size = SIGSTKSZ;
159	makecontext(&uc, switch_fn, 0);
160	raise(SIGUSR1);
161
162	err = sigaltstack(NULL, &stk);
163	if (err) {
164		perror("[FAIL]\tsigaltstack()");
165		exit(EXIT_FAILURE);
166	}
167	if (stk.ss_flags != SS_AUTODISARM) {
168		printf("[FAIL]\tss_flags=%i, should be SS_AUTODISARM\n",
169				stk.ss_flags);
170		exit(EXIT_FAILURE);
171	}
172	printf("[OK]\tsigaltstack is still SS_AUTODISARM after signal\n");
173
174	printf("[OK]\tTest passed\n");
175	return 0;
176}