libc/sys/t_mprotect.c

/* $NetBSD: t_mprotect.c,v 1.8 2019/07/16 17:29:18 martin Exp $ */

/*-
 * Copyright (c) 2011 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jukka Ruohonen.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
#include <sys/cdefs.h>
__RCSID("$NetBSD: t_mprotect.c,v 1.8 2019/07/16 17:29:18 martin Exp $");

#include <sys/param.h>
#include <sys/mman.h>
#include <sys/sysctl.h>
#include <sys/wait.h>

#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <atf-c.h>

#include "../common/exec_prot.h"

static long	page = 0;
static char	path[] = "mmap";

static void	sighandler(int);
static bool	paxinit(void);

static void
sighandler(int signo)
{
	_exit(signo);
}

static bool
paxinit(void)
{
	size_t len = sizeof(int);
	int pax_flags;
	int rv;

	rv = sysctlbyname("proc.curproc.paxflags",
	    &pax_flags, &len, NULL, 0);

	if (rv != 0)
		return false;

	return ((pax_flags & CTL_PROC_PAXFLAGS_MPROTECT) != 0);
}

ATF_TC_WITH_CLEANUP(mprotect_access);
ATF_TC_HEAD(mprotect_access, tc)
{
	atf_tc_set_md_var(tc, "descr", "Test for EACCES from mprotect(2)");
}

ATF_TC_BODY(mprotect_access, tc)
{
	int prot[2] = { PROT_NONE, PROT_READ };
	void *map;
	size_t i;
	int fd;

	fd = open(path, O_RDONLY | O_CREAT, 0600);
	ATF_REQUIRE(fd >= 0);

	/*
	 * The call should fail with EACCES if we try to mark
	 * a PROT_NONE or PROT_READ file/section as PROT_WRITE.
	 */
	for (i = 0; i < __arraycount(prot); i++) {

		map = mmap(NULL, page, prot[i], MAP_SHARED, fd, 0);

		if (map == MAP_FAILED)
			continue;

		errno = 0;

		ATF_REQUIRE(mprotect(map, page, PROT_WRITE) != 0);
		ATF_REQUIRE(errno == EACCES);
		ATF_REQUIRE(munmap(map, page) == 0);
	}

	ATF_REQUIRE(close(fd) == 0);
}

ATF_TC_CLEANUP(mprotect_access, tc)
{
	(void)unlink(path);
}

ATF_TC(mprotect_err);
ATF_TC_HEAD(mprotect_err, tc)
{
	atf_tc_set_md_var(tc, "descr", "Test error conditions of mprotect(2)");
}

ATF_TC_BODY(mprotect_err, tc)
{
	errno = 0;

	ATF_REQUIRE(mprotect((char *)-1, 1, PROT_READ) != 0);
	ATF_REQUIRE(errno == EINVAL);
}

ATF_TC(mprotect_exec);
ATF_TC_HEAD(mprotect_exec, tc)
{
	atf_tc_set_md_var(tc, "descr",
	    "Test mprotect(2) executable space protections");
}

/*
 * Trivial function -- should fit into a page
 */
ATF_TC_BODY(mprotect_exec, tc)
{
	pid_t pid;
	void *map;
	int sta, xp_support;

	xp_support = exec_prot_support();

	switch (xp_support) {
	case NOTIMPL:
		atf_tc_skip(
		    "Execute protection callback check not implemented");
		break;
	case NO_XP:
		atf_tc_skip(
		    "Host does not support executable space protection");
		break;
	case PARTIAL_XP: case PERPAGE_XP: default:
		break;
	}

	/*
	 * Map a page read/write and copy a trivial assembly function inside.
	 * We will then change the mapping rights:
	 * - first by setting the execution right, and check that we can
	 *   call the code found in the allocated page.
	 * - second by removing the execution right. This should generate
	 *   a SIGSEGV on architectures that can enforce --x permissions.
	 */

	map = mmap(NULL, page, PROT_MPROTECT(PROT_EXEC)|PROT_WRITE|PROT_READ,
	    MAP_ANON, -1, 0);
	ATF_REQUIRE(map != MAP_FAILED);

	memcpy(map, (void *)return_one,
	    (uintptr_t)return_one_end - (uintptr_t)return_one);

	/* give r-x rights then call code in page */
	ATF_REQUIRE(mprotect(map, page, PROT_EXEC|PROT_READ) == 0);
	ATF_REQUIRE(((int (*)(void))map)() == 1);

	/* remove --x right */
	ATF_REQUIRE(mprotect(map, page, PROT_READ) == 0);

	pid = fork();
	ATF_REQUIRE(pid >= 0);

	if (pid == 0) {
		ATF_REQUIRE(signal(SIGSEGV, sighandler) != SIG_ERR);
		ATF_CHECK(((int (*)(void))map)() == 1);
		_exit(0);
	}

	(void)wait(&sta);

	ATF_REQUIRE(munmap(map, page) == 0);

	ATF_REQUIRE(WIFEXITED(sta) != 0);

	switch (xp_support) {
	case PARTIAL_XP:
		/* Partial protection might fail; skip the test when it does */
		if (WEXITSTATUS(sta) != SIGSEGV) {
			atf_tc_skip("Host only supports "
			    "partial executable space protection");
		}
		break;
	case PERPAGE_XP: default:
		/* Per-page --x protection should not fail */
		ATF_REQUIRE(WEXITSTATUS(sta) == SIGSEGV);
		break;
	}
}

ATF_TC(mprotect_pax);
ATF_TC_HEAD(mprotect_pax, tc)
{
	atf_tc_set_md_var(tc, "descr", "PaX restrictions and mprotect(2)");
	atf_tc_set_md_var(tc, "require.user", "root");
}

ATF_TC_BODY(mprotect_pax, tc)
{
	const int prot[4] = { PROT_NONE, PROT_READ, PROT_WRITE };
	const char *str = NULL;
	void *map;
	size_t i;
	int rv;

	if (!paxinit())
		atf_tc_skip("PaX MPROTECT restrictions not enabled");

	/*
	 * As noted in the original PaX documentation [1],
	 * the following restrictions should apply:
	 *
	 *   (1) creating executable anonymous mappings
	 *
	 *   (2) creating executable/writable file mappings
	 *
	 *   (3) making a non-executable mapping executable
	 *
	 *   (4) making an executable/read-only file mapping
	 *       writable except for performing relocations
	 *       on an ET_DYN ELF file (non-PIC shared library)
	 *
	 *  The following will test only the case (3).
	 *
	 * [1] http://pax.grsecurity.net/docs/mprotect.txt
	 *
	 *     (Sun Apr 3 11:06:53 EEST 2011.)
	 */
	for (i = 0; i < __arraycount(prot); i++) {

		map = mmap(NULL, page, prot[i], MAP_ANON, -1, 0);

		if (map == MAP_FAILED)
			continue;

		rv = mprotect(map, 1, prot[i] | PROT_EXEC);

		(void)munmap(map, page);

		if (rv == 0) {
			str = "non-executable mapping made executable";
			goto out;
		}
	}

out:
	if (str != NULL)
		atf_tc_fail("%s", str);
}

ATF_TC(mprotect_write);
ATF_TC_HEAD(mprotect_write, tc)
{
	atf_tc_set_md_var(tc, "descr", "Test mprotect(2) write protections");
}

ATF_TC_BODY(mprotect_write, tc)
{
	pid_t pid;
	void *map;
	int sta;

	/*
	 * Map a page read/write, change the protection
	 * to read-only with mprotect(2), and try to write
	 * to the page. This should generate a SIGSEGV.
	 */
	map = mmap(NULL, page, PROT_WRITE|PROT_READ, MAP_ANON, -1, 0);
	ATF_REQUIRE(map != MAP_FAILED);

	ATF_REQUIRE(strlcpy(map, "XXX", 3) == 3);
	ATF_REQUIRE(mprotect(map, page, PROT_READ) == 0);

	pid = fork();
	ATF_REQUIRE(pid >= 0);

	if (pid == 0) {
		ATF_REQUIRE(signal(SIGSEGV, sighandler) != SIG_ERR);
		ATF_REQUIRE(strlcpy(map, "XXX", 3) == 0);
	}

	(void)wait(&sta);

	ATF_REQUIRE(WIFEXITED(sta) != 0);
	ATF_REQUIRE(WEXITSTATUS(sta) == SIGSEGV);
	ATF_REQUIRE(munmap(map, page) == 0);
}

ATF_TC(mprotect_mremap_exec);
ATF_TC_HEAD(mprotect_mremap_exec, tc)
{
	atf_tc_set_md_var(tc, "descr",
	    "Test mremap(2)+mprotect(2) executable space protections");
}

/*
 * Trivial function -- should fit into a page
 */
ATF_TC_BODY(mprotect_mremap_exec, tc)
{
	void *map, *map2;
	pid_t pid;
	int sta;

	/*
	 * Map a page read/write/exec and duplicate it.
	 * Map the copy executable.
	 * Copy a trivial assembly function to the writeable mapping.
	 * Try to execute it. This should never create a SIGSEGV.
	 */

	map = mmap(NULL, page, PROT_MPROTECT(PROT_EXEC|PROT_WRITE|PROT_READ),
	    MAP_ANON, -1, 0);
	ATF_REQUIRE(map != MAP_FAILED);
	map2 = mremap(map, page, NULL, page, MAP_REMAPDUP);
	ATF_REQUIRE(map2 != MAP_FAILED);
	ATF_REQUIRE(mprotect(map, page, PROT_WRITE|PROT_READ) == 0);
	ATF_REQUIRE(mprotect(map2, page, PROT_EXEC|PROT_READ) == 0);

	memcpy(map, (void *)return_one,
	    (uintptr_t)return_one_end - (uintptr_t)return_one);
	__builtin___clear_cache(map, (void *)((uintptr_t)map + page));

	ATF_REQUIRE(((int (*)(void))map2)() == 1);

	/* Double check that the executable mapping is not writeable. */
	pid = fork();
	ATF_REQUIRE(pid >= 0);

	if (pid == 0) {
		ATF_REQUIRE(signal(SIGSEGV, sighandler) != SIG_ERR);
		ATF_REQUIRE(strlcpy(map2, "XXX", 3) == 0);
	}

	(void)wait(&sta);

	ATF_REQUIRE(WIFEXITED(sta) != 0);
	ATF_REQUIRE(WEXITSTATUS(sta) == SIGSEGV);

	if (exec_prot_support() == PERPAGE_XP) {
		/* Double check that the writeable mapping is not executable. */
		pid = fork();
		ATF_REQUIRE(pid >= 0);

		if (pid == 0) {
			ATF_REQUIRE(signal(SIGSEGV, sighandler) != SIG_ERR);
			ATF_REQUIRE(((int (*)(void))map)() == 1);
		}

		(void)wait(&sta);

		ATF_REQUIRE(WIFEXITED(sta) != 0);
		ATF_REQUIRE(WEXITSTATUS(sta) == SIGSEGV);
	}

	ATF_REQUIRE(munmap(map, page) == 0);
	ATF_REQUIRE(munmap(map2, page) == 0);
}

ATF_TP_ADD_TCS(tp)
{
	page = sysconf(_SC_PAGESIZE);
	ATF_REQUIRE(page >= 0);

	ATF_TP_ADD_TC(tp, mprotect_access);
	ATF_TP_ADD_TC(tp, mprotect_err);
	ATF_TP_ADD_TC(tp, mprotect_exec);
	ATF_TP_ADD_TC(tp, mprotect_pax);
	ATF_TP_ADD_TC(tp, mprotect_write);
	ATF_TP_ADD_TC(tp, mprotect_mremap_exec);

	return atf_no_error();
}