1  /* Erasure of sensitive data, generic implementation.
       2     Copyright (C) 2016-2022 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  /* An assembler implementation of explicit_bzero can be created as an
      20     assembler alias of an optimized bzero implementation.
      21     Architecture-specific implementations also need to define
      22     __explicit_bzero_chk.  */
      23  
      24  #if !_LIBC
      25  # include <config.h>
      26  #endif
      27  
      28  /* memset_s need this define */
      29  #if HAVE_MEMSET_S
      30  # define __STDC_WANT_LIB_EXT1__ 1
      31  #endif
      32  
      33  #include <string.h>
      34  
      35  #if defined _WIN32 && !defined __CYGWIN__
      36  # define  WIN32_LEAN_AND_MEAN
      37  # include <windows.h>
      38  #endif
      39  
      40  #if _LIBC
      41  /* glibc-internal users use __explicit_bzero_chk, and explicit_bzero
      42     redirects to that.  */
      43  # undef explicit_bzero
      44  #endif
      45  
      46  /* Set LEN bytes of S to 0.  The compiler will not delete a call to
      47     this function, even if S is dead after the call.  */
      48  void
      49  explicit_bzero (void *s, size_t len)
      50  {
      51  #if defined _WIN32 && !defined __CYGWIN__
      52    (void) SecureZeroMemory (s, len);
      53  #elif HAVE_EXPLICIT_MEMSET
      54    explicit_memset (s, '\0', len);
      55  #elif HAVE_MEMSET_S
      56    (void) memset_s (s, len, '\0', len);
      57  #elif defined __GNUC__ && !defined __clang__
      58    memset (s, '\0', len);
      59    /* Compiler barrier.  */
      60    asm volatile ("" ::: "memory");
      61  #elif defined __clang__
      62    memset (s, '\0', len);
      63    /* Compiler barrier.  */
      64    /* With asm ("" ::: "memory") LLVM analyzes uses of 's' and finds that the
      65       whole thing is dead and eliminates it.  Use 'g' to work around this
      66       problem.  See <https://bugs.llvm.org/show_bug.cgi?id=15495#c11>.  */
      67    __asm__ volatile ("" : : "g"(s) : "memory");
      68  #else
      69    /* Invoke memset through a volatile function pointer.  This defeats compiler
      70       optimizations.  */
      71    void * (* const volatile volatile_memset) (void *, int, size_t) = memset;
      72    (void) volatile_memset (s, '\0', len);
      73  #endif
      74  }