xref: /xnu-10063.121.3/osfmk/corecrypto/cc_clear.c (revision 2c2f96dc2b9a4408a43d3150ae9c105355ca3daa)

/* Copyright (c) (2014-2019,2021,2022) Apple Inc. All rights reserved.
 *
 * corecrypto is licensed under Apple Inc.’s Internal Use License Agreement (which
 * is contained in the License.txt file distributed with corecrypto) and only to
 * people who accept that license. IMPORTANT:  Any license rights granted to you by
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 * devices and computers you own or control, for the sole purpose of verifying the
 * security characteristics and correct functioning of the Apple Software.  You may
 * not, directly or indirectly, redistribute the Apple Software or any portions thereof.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
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 */

#include "cc_internal.h"
#include <corecrypto/cc.h>
#include <corecrypto/cc_config.h>
#include "fipspost_trace.h"

#if CC_HAS_SECUREZEROMEMORY
#include <windows.h>
#endif

#if !(CC_HAS_MEMSET_S || CC_HAS_SECUREZEROMEMORY || CC_HAS_EXPLICIT_BZERO)
/*
 * Pointer to memset is volatile so that the compiler must dereference
 * it and can't assume it points to any function in particular
 * (such as memset, which it then might further "optimize").
 */
    #if CC_EFI
static void(*const volatile zero_mem_ptr)(void *, size_t) = EfiCommonLibZeroMem;
    #else
static void* (*const volatile memset_ptr)(void*, int, size_t) = memset;
    #endif
#endif

void
cc_clear(size_t len, void *dst)
{
	FIPSPOST_TRACE_EVENT;

#if CC_HAS_MEMSET_S
	memset_s(dst, len, 0, len);
#elif CC_HAS_SECUREZEROMEMORY
	SecureZeroMemory(dst, len);
#elif CC_HAS_EXPLICIT_BZERO
	explicit_bzero(dst, len);
#else
    #if CC_EFI
	(zero_mem_ptr)(dst, len);
    #else
	(memset_ptr)(dst, 0, len);
    #endif

	/* One more safeguard, should all hell break loose - a memory barrier.
	 * The volatile function pointer _should_ work, but compilers are by
	 * spec allowed to load `memset_ptr` into a register and skip the
	 * call if `memset_ptr == memset`. However, too many systems rely
	 * on such behavior for compilers to try and optimize it. */
	__asm__ __volatile__ ("" : : "r"(dst) : "memory");
#endif
}