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__ */