util: add facility to check for RWX page support

Some code won't work well when the OS doesn't allow RWX pages. This
page introduces a check for runtime evaluation of the OS' policy on
this.

Thanks to Shawn Webb from HardenedBSD for suggesting this solution.

src/Makefile.am

@@ -392,6 +392,7 @@ util-mpm-ac-tile-small.c \
util-mpm-hs.c util-mpm-hs.h \
util-mpm.c util-mpm.h \
util-optimize.h \
util-pages.c util-pages.h \
util-path.c util-path.h \
util-pidfile.c util-pidfile.h \
util-pool.c util-pool.h \

src/util-pages.c

@@ -0,0 +1,58 @@
/* Copyright (C) 2016 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

/**
 * \file
 *
 * \author Victor Julien <victor@inliniac.net>
 *
 * Page util functions
 */

#include "suricata-common.h"
#ifndef HAVE_SYS_MMAN_H
#define PageSupportsRWX 1
#else
#include <sys/mman.h>

/** \brief check if OS allows for RWX pages
 *
 *  Some OS' disallow RWX pages for security reasons. This function mmaps
 *  some memory RW and then tries to turn it into RWX. If this fails we
 *  assume that the OS doesn't allow for this.
 *
 *  Thanks to Shawn Webb from HardenedBSD for the suggestion.
 *
 *  \retval 1 RWX supported
 *  \retval 0 not supported
 */
int PageSupportsRWX(void)
{
    int retval = 1;
    void *ptr;
    ptr = mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);
    if (ptr != MAP_FAILED) {
        if (mprotect(ptr, getpagesize(), PROT_READ|PROT_WRITE|PROT_EXEC) == -1) {
            SCLogConfig("RWX pages denied by OS");
            retval = 0;
        }
        munmap(ptr, getpagesize());
    }
    return retval;
}
#endif /* HAVE_SYS_MMAN_H */

src/util-pages.h

@@ -0,0 +1,42 @@
/* Copyright (C) 2016 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

/**
 * \file
 *
 * \author Victor Julien <victor@inliniac.net>
 *
 */

#ifndef __UTIL_PAGES_H__
#define __UTIL_PAGES_H__

#include "suricata-common.h"

#ifdef __OpenBSD__
    /* OpenBSD won't allow for this test:
     * "suricata(...): mprotect W^X violation" */
    #define PageSupportsRWX() 0
#else
    #ifndef HAVE_SYS_MMAN_H
        #define PageSupportsRWX() 1
    #else
        int PageSupportsRWX(void);
    #endif /* HAVE_SYS_MMAN_H */
#endif

#endif /* __UTIL_PAGES_H__ */