rdgsbase.c

/* $Id: rdgsbase.c,v 1.9 2017/08/13 16:22:01 kostik Exp kostik $ */

#include <sys/param.h>
#include <sys/sysctl.h>
#include <err.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <machine/sysarch.h>

static inline uint64_t
rdgsbase(void)
{
	uint64_t x;

	__asm __volatile("rdgsbase %0" : "=r" (x));
	return (x);
}

static inline void
wrgsbase(uint64_t x)
{

	__asm __volatile("wrgsbase %0" : : "r" (x));
}

static inline uint64_t
rdfsbase(void)
{
	uint64_t x;

	__asm __volatile("rdfsbase %0" : "=r" (x));
	return (x);
}

static inline void
wrfsbase(uint64_t x)
{

	__asm __volatile("wrfsbase %0" : : "r" (x));
}

static void *
rungs(void *arg __unused)
{
	volatile char x[1024];
	unsigned i;
	uint64_t y, oldbase;

	oldbase = rdgsbase();
	for (i = 0;;) {
		wrgsbase((uintptr_t)&x[i]);
		if (rdgsbase() != (uintptr_t)&x[i]) {
			wrgsbase(oldbase);
			printf("bug1 %lx %lx\n", rdgsbase(), (uintptr_t)&x[i]);
			exit(1);
		}
		sysarch(AMD64_GET_GSBASE, &y);
		if (y != (uintptr_t)&x[i]) {
			wrgsbase(oldbase);
			printf("bug2 %lx %lx\n", y, (uintptr_t)&x[i]);
			exit(1);
		}
		i++;
		if (i >= nitems(x))
			i = 0;
	}
	return (NULL);
}

static void *
runfs(void *arg __unused)
{
	volatile char x[1024];
	unsigned i;
	uint64_t y, oldbase;

	oldbase = rdfsbase();
	for (i = 0;;) {
		wrfsbase((uintptr_t)&x[i]);
		if (rdfsbase() != (uintptr_t)&x[i]) {
			wrfsbase(oldbase);
			printf("bug3 %lx %lx\n", rdfsbase(), (uintptr_t)&x[i]);
			exit(1);
		}
		sysarch(AMD64_GET_FSBASE, &y);
		if (y != (uintptr_t)&x[i]) {
			wrfsbase(oldbase);
			printf("bug4 %lx %lx\n", y, (uintptr_t)&x[i]);
			exit(1);
		}
		i++;
		if (i > nitems(x))
			i = 0;
	}
	return (NULL);
}

static void
start(int nthreads)
{
	pthread_t thrs[nthreads * 2];
	int error, i;

	for (i = 0; i < nthreads; i++) {
		error = pthread_create(&thrs[i], NULL, rungs, NULL);
		if (error != 0)
			errc(1, error, "pthread_create");
	}
	for (; i < 2 * nthreads; i++) {
		error = pthread_create(&thrs[i], NULL, runfs, NULL);
		if (error != 0)
			errc(1, error, "pthread_create");
	}
}

int
main(void)
{
	static const int mib[2] = {CTL_HW, HW_NCPU};
	int error, nthreads;
	size_t len;

	len = sizeof(nthreads);
	error = sysctl(mib, nitems(mib), &nthreads, &len, NULL, 0);
	if (error == -1)
		err(1, "sysctl hw.ncpu");
	start(nthreads);
	for (;;)
		pause();
}