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