I/O port permission bit inheritance between threads

[Stephen Hemminger <stephen@networkplumber.org>]

ioperm() inheritance across threads is different in KVM then when run
on physical hardware.  The following program runs on physical hardware
but get SEGV under KVM.

It appears that the I/O permission bits are not shared between threads
in the same way.

/* Original Copyright 2011, Kees Cook <kees@outflux.net>, License: GPLv2 */
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#include <sys/io.h>

static void *beep(void *arg)
{
	unsigned char bits;

	fprintf(stderr, "waiting\n");
	sleep(1);

	fprintf(stderr, "beeping\n");
	/* turn on speaker */
	bits = inb(0x61);
	bits |= 3;
	outb(bits, 0x61);

	/* set 1000 Hz frequency */
	bits = 0xA9;
	outb(bits, 0x42);
	bits = 0x04;
	outb(bits, 0x42);

	/* listen to the beep */
	sleep(4);
	fprintf(stderr, "done\n");

	return NULL;
}

int main() {
	pthread_t tid;
	unsigned char orig;

	if (pthread_create(&tid, NULL, &beep, NULL)) {
		perror("pthread");
		return 1;
	}

	/* gain access to speaker control port */
	if (ioperm(0x61, 0x61, 1) < 0) {
		perror("0x61");
		return 1;
	}
	orig = inb(0x61);

	/* gain access to speaker frequency port */
	if (ioperm(0x42, 0x42, 1) < 0) {
		perror("0x42");
		return 2;
	}

	fprintf(stderr, "joining\n");
	pthread_join(tid, NULL);
	
	/* restore speaker bits to turn off speaker */
	outb(orig, 0x61);
	fprintf(stderr, "done\n");
	return 0;
}