ssp: add Object Size Checking common code

The Object Size Checking (-D_FORTIFY_SOURCE=*) functionality provides
wrappers around functions suspectible to buffer overflows.  While
independent from Stack Smashing Protection (-fstack-protector*), they
are often used and implemented together.

While GCC also provides an implementation in libssp, it is completely
broken (CVE-2016-4973, RHBZ#1324759) and seemingly unfixable, as there
is no reliable way for a preprocessor macro to trigger a link flag.
Therefore, adding this here is necessary to make it work.

Note that this does require building gcc with --disable-libssp and
gcc_cv_libc_provides_ssp=yes.

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

newlib/libc/include/ssp/ssp.h

@@ -0,0 +1,77 @@
+/*	$NetBSD: ssp.h,v 1.13 2015/09/03 20:43:47 plunky Exp $	*/
+
+/*-
+ * Copyright (c) 2006, 2011 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Christos Zoulas.
+ *
+ * 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.
+ */
+#ifndef _SSP_SSP_H_
+#define _SSP_SSP_H_
+
+#include <sys/cdefs.h>
+
+/* __ssp_real is used by the implementation in libc */
+#if __SSP_FORTIFY_LEVEL == 0
+#define __ssp_real_(fun)	fun
+#else
+#define __ssp_real_(fun)	__ssp_real_ ## fun
+#endif
+#define __ssp_real(fun)		__ssp_real_(fun)
+
+#define __ssp_inline extern __inline__ __attribute__((__always_inline__, __gnu_inline__))
+
+#define __ssp_bos(ptr) __builtin_object_size(ptr, __SSP_FORTIFY_LEVEL > 1)
+#define __ssp_bos0(ptr) __builtin_object_size(ptr, 0)
+
+#define __ssp_check(buf, len, bos) \
+	if (bos(buf) != (size_t)-1 && len > bos(buf)) \
+		__chk_fail()
+#define __ssp_decl(rtype, fun, args) \
+rtype __ssp_real_(fun) args __asm__(__ASMNAME(#fun)); \
+__ssp_inline rtype fun args __asm__(__ASMNAME("__ssp_protected_" #fun)); \
+__ssp_inline rtype fun args
+#define __ssp_redirect_raw(rtype, fun, args, call, cond, bos) \
+__ssp_decl(rtype, fun, args) \
+{ \
+	if (cond) \
+		__ssp_check(__buf, __len, bos); \
+	return __ssp_real_(fun) call; \
+}
+
+#define __ssp_redirect(rtype, fun, args, call) \
+    __ssp_redirect_raw(rtype, fun, args, call, 1, __ssp_bos)
+#define __ssp_redirect0(rtype, fun, args, call) \
+    __ssp_redirect_raw(rtype, fun, args, call, 1, __ssp_bos0)
+
+#define __ssp_overlap(a, b, l) \
+    (((a) <= (b) && (b) < (a) + (l)) || ((b) <= (a) && (a) < (b) + (l)))
+
+__BEGIN_DECLS
+void __stack_chk_fail(void) __dead2;
+void __chk_fail(void) __dead2;
+__END_DECLS
+
+#endif /* _SSP_SSP_H_ */

newlib/libc/include/sys/features.h

@@ -100,6 +100,9 @@ extern "C" {
  * _SVID_SOURCE (deprecated by _DEFAULT_SOURCE)
  * _DEFAULT_SOURCE (or none of the above)
  * 	POSIX-1.2008 with BSD and SVr4 extensions
+ *
+ * _FORTIFY_SOURCE = 1 or 2
+ * 	Object Size Checking function wrappers
  */
 
 #ifdef _GNU_SOURCE
@@ -233,9 +236,11 @@ extern "C" {
  * __GNU_VISIBLE
  * 	GNU extensions; enabled with _GNU_SOURCE.
  *
+ * __SSP_FORTIFY_LEVEL
+ * 	Object Size Checking; defined to 0 (off), 1, or 2.
+ *
  * In all cases above, "enabled by default" means either by defining
  * _DEFAULT_SOURCE, or by not defining any of the public feature test macros.
- * Defining _GNU_SOURCE makes all of the above avaliable.
  */
 
 #ifdef _ATFILE_SOURCE
@@ -314,6 +319,17 @@ extern "C" {
 #define	__XSI_VISIBLE		0
 #endif
 
+#if _FORTIFY_SOURCE > 0 && !defined(__cplusplus) && !defined(__lint__) && \
+   (__OPTIMIZE__ > 0 || defined(__clang__)) && __GNUC_PREREQ__(4, 1)
+#  if _FORTIFY_SOURCE > 1
+#    define __SSP_FORTIFY_LEVEL 2
+#  else
+#    define __SSP_FORTIFY_LEVEL 1
+#  endif
+#else
+#  define __SSP_FORTIFY_LEVEL 0
+#endif
+
 /* RTEMS adheres to POSIX -- 1003.1b with some features from annexes.  */
 
 #ifdef __rtems__

newlib/libc/ssp/chk_fail.c

@@ -0,0 +1,13 @@
+#include <signal.h>
+#include <string.h>
+#include <unistd.h>
+
+void
+__attribute__((__noreturn__))
+__chk_fail(void)
+{
+  char msg[] = "*** buffer overflow detected ***: terminated\n";
+  write (2, msg, strlen (msg));
+  raise (SIGABRT);
+  _exit (127);
+}