tools/testing/selftests/sigaltstack/sas.c

/*
 * Stas Sergeev <stsp@users.sourceforge.net>
 *
 * test sigaltstack(SS_ONSTACK | SS_AUTODISARM)
 * If that succeeds, then swapcontext() can be used inside sighandler safely.
 *
 */

#define _GNU_SOURCE
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <ucontext.h>
#include <alloca.h>
#include <string.h>
#include <assert.h>

#ifndef SS_AUTODISARM
#define SS_AUTODISARM  (1 << 4)
#endif

static void *sstack, *ustack;
static ucontext_t uc, sc;
static const char *msg = "[OK]\tStack preserved";
static const char *msg2 = "[FAIL]\tStack corrupted";
struct stk_data {
	char msg[128];
	int flag;
};

void my_usr1(int sig, siginfo_t *si, void *u)
{
	char *aa;
	int err;
	stack_t stk;
	struct stk_data *p;

	register unsigned long sp asm("sp");

	if (sp < (unsigned long)sstack ||
			sp >= (unsigned long)sstack + SIGSTKSZ) {
		printf("[FAIL]\tSP is not on sigaltstack\n");
		exit(EXIT_FAILURE);
	}
	/* put some data on stack. other sighandler will try to overwrite it */
	aa = alloca(1024);
	assert(aa);
	p = (struct stk_data *)(aa + 512);
	strcpy(p->msg, msg);
	p->flag = 1;
	printf("[RUN]\tsignal USR1\n");
	err = sigaltstack(NULL, &stk);
	if (err) {
		perror("[FAIL]\tsigaltstack()");
		exit(EXIT_FAILURE);
	}
	if (stk.ss_flags != SS_DISABLE)
		printf("[FAIL]\tss_flags=%i, should be SS_DISABLE\n",
				stk.ss_flags);
	else
		printf("[OK]\tsigaltstack is disabled in sighandler\n");
	swapcontext(&sc, &uc);
	printf("%s\n", p->msg);
	if (!p->flag) {
		printf("[RUN]\tAborting\n");
		exit(EXIT_FAILURE);
	}
}

void my_usr2(int sig, siginfo_t *si, void *u)
{
	char *aa;
	struct stk_data *p;

	printf("[RUN]\tsignal USR2\n");
	aa = alloca(1024);
	/* dont run valgrind on this */
	/* try to find the data stored by previous sighandler */
	p = memmem(aa, 1024, msg, strlen(msg));
	if (p) {
		printf("[FAIL]\tsigaltstack re-used\n");
		/* corrupt the data */
		strcpy(p->msg, msg2);
		/* tell other sighandler that his data is corrupted */
		p->flag = 0;
	}
}

static void switch_fn(void)
{
	printf("[RUN]\tswitched to user ctx\n");
	raise(SIGUSR2);
	setcontext(&sc);
}

int main(void)
{
	struct sigaction act;
	stack_t stk;
	int err;

	sigemptyset(&act.sa_mask);
	act.sa_flags = SA_ONSTACK | SA_SIGINFO;
	act.sa_sigaction = my_usr1;
	sigaction(SIGUSR1, &act, NULL);
	act.sa_sigaction = my_usr2;
	sigaction(SIGUSR2, &act, NULL);
	sstack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
		      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
	if (sstack == MAP_FAILED) {
		perror("mmap()");
		return EXIT_FAILURE;
	}
	stk.ss_sp = sstack;
	stk.ss_size = SIGSTKSZ;
	stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
	err = sigaltstack(&stk, NULL);
	if (err) {
		perror("[FAIL]\tsigaltstack(SS_ONSTACK | SS_AUTODISARM)");
		stk.ss_flags = SS_ONSTACK;
	}
	err = sigaltstack(&stk, NULL);
	if (err) {
		perror("[FAIL]\tsigaltstack(SS_ONSTACK)");
		return EXIT_FAILURE;
	}

	ustack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
		      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
	if (ustack == MAP_FAILED) {
		perror("mmap()");
		return EXIT_FAILURE;
	}
	getcontext(&uc);
	uc.uc_link = NULL;
	uc.uc_stack.ss_sp = ustack;
	uc.uc_stack.ss_size = SIGSTKSZ;
	makecontext(&uc, switch_fn, 0);
	raise(SIGUSR1);

	err = sigaltstack(NULL, &stk);
	if (err) {
		perror("[FAIL]\tsigaltstack()");
		exit(EXIT_FAILURE);
	}
	if (stk.ss_flags != 0) {
		printf("[FAIL]\tss_flags=%i, should be 0\n",
				stk.ss_flags);
		exit(EXIT_FAILURE);
	}
	printf("[OK]\tsigaltstack is enabled after signal\n");

	printf("[OK]\tTest passed\n");
	return 0;
}