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85 lines
2.3 KiB
C
85 lines
2.3 KiB
C
#include "memzero.h"
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#ifndef __STDC_WANT_LIB_EXT1__
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#define __STDC_WANT_LIB_EXT1__ 1 // C11's bounds-checking interface.
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#endif
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#include <string.h>
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#ifdef _WIN32
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#include <Windows.h>
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#endif
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#ifdef __unix__
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#include <strings.h>
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#include <sys/param.h>
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#endif
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// C11's bounds-checking interface.
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#if defined(__STDC_LIB_EXT1__)
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#define HAVE_MEMSET_S 1
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#endif
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// GNU C Library version 2.25 or later.
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#if defined(__GLIBC__) && \
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(__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25))
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#define HAVE_EXPLICIT_BZERO 1
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#endif
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// Newlib
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#if defined(__NEWLIB__)
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#define HAVE_EXPLICIT_BZERO 1
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#endif
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// FreeBSD version 11.0 or later.
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#if defined(__FreeBSD__) && __FreeBSD_version >= 1100037
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#define HAVE_EXPLICIT_BZERO 1
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#endif
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// OpenBSD version 5.5 or later.
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#if defined(__OpenBSD__) && OpenBSD >= 201405
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#define HAVE_EXPLICIT_BZERO 1
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#endif
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// NetBSD version 7.2 or later.
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#if defined(__NetBSD__) && __NetBSD_Version__ >= 702000000
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#define HAVE_EXPLICIT_MEMSET 1
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#endif
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// Adapted from
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// https://github.com/jedisct1/libsodium/blob/1647f0d53ae0e370378a9195477e3df0a792408f/src/libsodium/sodium/utils.c#L102-L130
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void memzero(void *const pnt, const size_t len) {
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#ifdef _WIN32
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SecureZeroMemory(pnt, len);
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#elif defined(HAVE_MEMSET_S)
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memset_s(pnt, (rsize_t)len, 0, (rsize_t)len);
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#elif defined(HAVE_EXPLICIT_BZERO)
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bzero(pnt, len);
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#elif defined(HAVE_EXPLICIT_MEMSET)
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explicit_memset(pnt, 0, len);
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#else
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volatile unsigned char *volatile pnt_ = (volatile unsigned char *volatile)pnt;
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size_t i = (size_t)0U;
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while (i < len) {
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pnt_[i++] = 0U;
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}
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/* Memory barrier that scares the compiler away from optimizing out
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* the above loop.
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*
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* Quoting Adam Langley <agl@google.com> in commit
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* ad1907fe73334d6c696c8539646c21b11178f20f of BoringSSL (ISC License):
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*
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* As best as we can tell, this is sufficient to break any optimisations
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* that might try to eliminate "superfluous" memsets. This method is used
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* in memzero_explicit() the Linux kernel, too. Its advantage is that it
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* is pretty efficient because the compiler can still implement the
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* memset() efficiently, just not remove it entirely. See "Dead Store
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* Elimination (Still) Considered Harmful" by Yang et al. (USENIX Security
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* 2017) for more background.
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*/
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__asm__ __volatile__("" : : "r"(pnt_) : "memory");
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#endif
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}
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