1 files changed, 74 insertions, 0 deletions

diff --git a/lib/explicit_bzero.c b/lib/explicit_bzero.c
new file mode 100644
index 00000000000..c33cab9e6d5
--- /dev/null
+++ b/lib/explicit_bzero.c
@@ -0,0 +1,74 @@
+/* Erasure of sensitive data, generic implementation.
+   Copyright (C) 2016-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+/* An assembler implementation of explicit_bzero can be created as an
+   assembler alias of an optimized bzero implementation.
+   Architecture-specific implementations also need to define
+   __explicit_bzero_chk.  */
+
+#if !_LIBC
+# include <config.h>
+#endif
+
+/* memset_s need this define */
+#if HAVE_MEMSET_S
+# define __STDC_WANT_LIB_EXT1__ 1
+#endif
+
+#include <string.h>
+
+#if defined _WIN32 && !defined __CYGWIN__
+# define  WIN32_LEAN_AND_MEAN
+# include <windows.h>
+#endif
+
+#if _LIBC
+/* glibc-internal users use __explicit_bzero_chk, and explicit_bzero
+   redirects to that.  */
+# undef explicit_bzero
+#endif
+
+/* Set LEN bytes of S to 0.  The compiler will not delete a call to
+   this function, even if S is dead after the call.  */
+void
+explicit_bzero (void *s, size_t len)
+{
+#if defined _WIN32 && !defined __CYGWIN__
+  (void) SecureZeroMemory (s, len);
+#elif HAVE_EXPLICIT_MEMSET
+  explicit_memset (s, '\0', len);
+#elif HAVE_MEMSET_S
+  (void) memset_s (s, len, '\0', len);
+#elif defined __GNUC__ && !defined __clang__
+  memset (s, '\0', len);
+  /* Compiler barrier.  */
+  asm volatile ("" ::: "memory");
+#elif defined __clang__
+  memset (s, '\0', len);
+  /* Compiler barrier.  */
+  /* With asm ("" ::: "memory") LLVM analyzes uses of 's' and finds that the
+     whole thing is dead and eliminates it.  Use 'g' to work around this
+     problem.  See <https://bugs.llvm.org/show_bug.cgi?id=15495#c11>.  */
+  __asm__ volatile ("" : : "g"(s) : "memory");
+#else
+  /* Invoke memset through a volatile function pointer.  This defeats compiler
+     optimizations.  */
+  void * (* const volatile volatile_memset) (void *, int, size_t) = memset;
+  (void) volatile_memset (s, '\0', len);
+#endif
+}