New string function explicit_bzero (from OpenBSD).

explicit_bzero(s, n) is the same as memset(s, 0, n), except that the
compiler is not allowed to delete a call to explicit_bzero even if the
memory pointed to by 's' is dead after the call.  Right now, this effect
is achieved externally by having explicit_bzero be a function whose
semantics are unknown to the compiler, and internally, with a no-op
asm statement that clobbers memory.  This does mean that small
explicit_bzero operations cannot be expanded inline as small memset
operations can, but on the other hand, small memset operations do get
deleted by the compiler.  Hopefully full compiler support for
explicit_bzero will happen relatively soon.

There are two new tests: test-explicit_bzero.c verifies the
visible semantics in the same way as the existing test-bzero.c,
and tst-xbzero-opt.c verifies the not-being-optimized-out property.
The latter is conceptually based on a test written by Matthew Dempsky
for the OpenBSD regression suite.

The crypt() implementation has an immediate use for this new feature.
We avoid having to add a GLIBC_PRIVATE alias for explicit_bzero
by running all of libcrypt's calls through the fortified variant,
__explicit_bzero_chk, which is in the impl namespace anyway.  Currently
I'm not aware of anything in libc proper that needs this, but the
glue is all in place if it does become necessary.  The legacy DES
implementation wasn't bothering to clear its buffers, so I added that,
mostly for consistency's sake.

	* string/explicit_bzero.c: New routine.
	* string/test-explicit_bzero.c, string/tst-xbzero-opt.c: New tests.
	* string/Makefile (routines, strop-tests, tests): Add them.
	* string/test-memset.c: Add ifdeffage for testing explicit_bzero.
	* string/string.h [__USE_MISC]: Declare explicit_bzero.

	* debug/explicit_bzero_chk.c: New routine.
	* debug/Makefile (routines): Add it.
	* debug/tst-chk1.c: Test fortification of explicit_bzero.
	* string/bits/string3.h: Fortify explicit_bzero.

	* manual/string.texi: Document explicit_bzero.
	* NEWS: Mention addition of explicit_bzero.

	* crypt/crypt-entry.c (__crypt_r): Clear key-dependent intermediate
	data before returning, using explicit_bzero.
	* crypt/md5-crypt.c (__md5_crypt_r): Likewise.
	* crypt/sha256-crypt.c (__sha256_crypt_r): Likewise.
	* crypt/sha512-crypt.c (__sha512_crypt_r): Likewise.

	* include/string.h: Redirect internal uses of explicit_bzero
	to __explicit_bzero_chk[_internal].
	* string/Versions [GLIBC_2.25]: Add explicit_bzero.
	* debug/Versions [GLIBC_2.25]: Add __explicit_bzero_chk.
	* sysdeps/arm/nacl/libc.abilist
	* sysdeps/unix/sysv/linux/aarch64/libc.abilist
	* sysdeps/unix/sysv/linux/alpha/libc.abilist
	* sysdeps/unix/sysv/linux/arm/libc.abilist
	* sysdeps/unix/sysv/linux/hppa/libc.abilist
	* sysdeps/unix/sysv/linux/i386/libc.abilist
	* sysdeps/unix/sysv/linux/ia64/libc.abilist
	* sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
	* sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
	* sysdeps/unix/sysv/linux/microblaze/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist
	* sysdeps/unix/sysv/linux/nios2/libc.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist
	* sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist
	* sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist
	* sysdeps/unix/sysv/linux/sh/libc.abilist
	* sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist
	* sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist
	* sysdeps/unix/sysv/linux/tile/tilepro/libc.abilist
	* sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
	* sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist:
	Add entries for explicit_bzero and __explicit_bzero_chk.

4 files changed, 76 insertions, 0 deletions

diff --git a/debug/Makefile b/debug/Makefile
index 6b5f31e..84d3f92 100644
--- a/debug/Makefile
+++ b/debug/Makefile
@@ -48,6 +48,7 @@ routines  = backtrace backtracesyms backtracesymsfd noophooks \
 	    vdprintf_chk obprintf_chk \
 	    longjmp_chk ____longjmp_chk \
 	    fdelt_chk poll_chk ppoll_chk \
+	    explicit_bzero_chk \
 	    stack_chk_fail fortify_fail \
 	    $(static-only-routines)
 static-only-routines := warning-nop stack_chk_fail_local
diff --git a/debug/Versions b/debug/Versions
index 0482c85..a6628db 100644
--- a/debug/Versions
+++ b/debug/Versions
@@ -55,6 +55,9 @@ libc {
   GLIBC_2.16 {
     __poll_chk; __ppoll_chk;
   }
+  GLIBC_2.25 {
+    __explicit_bzero_chk;
+  }
   GLIBC_PRIVATE {
     __fortify_fail;
   }
diff --git a/debug/explicit_bzero_chk.c b/debug/explicit_bzero_chk.c
new file mode 100644
index 0000000..2e507f8
--- /dev/null
+++ b/debug/explicit_bzero_chk.c
@@ -0,0 +1,44 @@
+/* Generic implementation of __explicit_bzero_chk.
+   Copyright (C) 1991-2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Torbjorn Granlund (tege@sics.se).
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This is the generic definition of __explicit_bzero_chk.  The
+   __explicit_bzero_chk symbol is used as the implementation of
+   explicit_bzero throughout glibc.  If this file is overriden by an
+   architecture, both __explicit_bzero_chk and
+   __explicit_bzero_chk_internal have to be defined (the latter not as
+   an IFUNC).  */
+
+#include <string.h>
+
+void
+__explicit_bzero_chk (void *dst, size_t len, size_t dstlen)
+{
+  /* Inline __memset_chk to avoid a PLT reference to __memset_chk.  */
+  if (__glibc_unlikely (dstlen < len))
+    __chk_fail ();
+  memset (dst, '\0', len);
+  /* Compiler barrier.  */
+  asm volatile ("" ::: "memory");
+}
+
+/* libc-internal references use the hidden
+   __explicit_bzero_chk_internal symbol.  This is necessary if
+   __explicit_bzero_chk is implemented as an IFUNC because some
+   targets do not support hidden references to IFUNC symbols.  */
+strong_alias (__explicit_bzero_chk, __explicit_bzero_chk_internal)
diff --git a/debug/tst-chk1.c b/debug/tst-chk1.c
index 478c2fb..e87a279 100644
--- a/debug/tst-chk1.c
+++ b/debug/tst-chk1.c
@@ -160,6 +160,10 @@ do_test (void)
   if (memcmp (buf, "aabcdabc\0\0", 10))
     FAIL ();
 
+  explicit_bzero (buf + 6, 4);
+  if (memcmp (buf, "aabcda\0\0\0\0", 10))
+    FAIL ();
+
   strcpy (buf + 4, "EDCBA");
   if (memcmp (buf, "aabcEDCBA", 10))
     FAIL ();
@@ -201,6 +205,10 @@ do_test (void)
   if (memcmp (buf, "aabcdabc\0\0", 10))
     FAIL ();
 
+  explicit_bzero (buf + 6, l0 + 4);
+  if (memcmp (buf, "aabcda\0\0\0\0", 10))
+    FAIL ();
+
   strcpy (buf + 4, str1 + 5);
   if (memcmp (buf, "aabcEDCBA", 10))
     FAIL ();
@@ -256,6 +264,10 @@ do_test (void)
   if (memcmp (a.buf1, "aabcdabc\0\0", 10))
     FAIL ();
 
+  explicit_bzero (a.buf1 + 6, l0 + 4);
+  if (memcmp (a.buf1, "aabcda\0\0\0\0", 10))
+    FAIL ();
+
 #if __USE_FORTIFY_LEVEL < 2
   /* The following tests are supposed to crash with -D_FORTIFY_SOURCE=2
      and sufficient GCC support, as the string operations overflow
@@ -346,6 +358,14 @@ do_test (void)
   CHK_FAIL_END
 
   CHK_FAIL_START
+  explicit_bzero (buf + 9, 2);
+  CHK_FAIL_END
+
+  CHK_FAIL_START
+  explicit_bzero (buf + 9, l0 + 2);
+  CHK_FAIL_END
+
+  CHK_FAIL_START
   strcpy (buf + 5, str1 + 5);
   CHK_FAIL_END
 
@@ -454,6 +474,14 @@ do_test (void)
   bzero (a.buf1 + 9, l0 + 2);
   CHK_FAIL_END
 
+  CHK_FAIL_START
+  explicit_bzero (a.buf1 + 9, 2);
+  CHK_FAIL_END
+
+  CHK_FAIL_START
+  explicit_bzero (a.buf1 + 9, l0 + 2);
+  CHK_FAIL_END
+
 # if __USE_FORTIFY_LEVEL >= 2
 #  define O 0
 # else