$NetBSD: explicit_memset.3,v 1.3 2024/11/02 02:43:48 riastradh Exp $
Copyright (c) 2013 The NetBSD Foundation, Inc.
All rights reserved.
This documentation is derived from text contributed to The NetBSD
Foundation by Taylor R. Campbell.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
.Dd November 1, 2024 .Dt EXPLICIT_MEMSET 3 .Os .Sh NAME .Nm explicit_memset .Nm memset_explicit .Nd guarantee writing a byte to a byte string .Sh LIBRARY .Lb libc .Sh SYNOPSIS n string.h .Ft void * .Fn explicit_memset "void *b" "int c" "size_t len" .Ft void * .Fn memset_explicit "void *b" "int c" "size_t len" .Sh DESCRIPTION The .Fn explicit_memset and .Fn memset_explicit functions write .Fa len bytes of value .Fa c (converted to an unsigned char) to the string .Fa b . They are guaranteed not to be optimized away by the compiler even if .Fa b is no longer used and is about to be freed or go out of scope. .Sh RETURN VALUES The .Fn explicit_memset function returns the original value of .Fa b . .Sh EXAMPLES Create a buffer on the stack for a secret key, use it, and then zero it in memory before throwing it away. d -literal -offset indent void f(void) { uint8_t key[32]; crypto_random(key, sizeof(key)); do_crypto_stuff(key, sizeof(key)); ... explicit_memset(key, 0, sizeof(key)); } .Ed .Sh SEE ALSO .Xr consttime_memequal 3 , .Xr memset 3 .Sh STANDARDS The .Fn memset_explicit function conforms to .St -isoC-2023 . .Sh HISTORY The .Fn explicit_memset function appeared in .Nx 7.0 . The .Fn memset_explicit alias was added in .Nx 11.0 .
Copyright (c) 2013 The NetBSD Foundation, Inc.
All rights reserved.
This documentation is derived from text contributed to The NetBSD
Foundation by Taylor R. Campbell.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
.Dd November 1, 2024 .Dt EXPLICIT_MEMSET 3 .Os .Sh NAME .Nm explicit_memset .Nm memset_explicit .Nd guarantee writing a byte to a byte string .Sh LIBRARY .Lb libc .Sh SYNOPSIS n string.h .Ft void * .Fn explicit_memset "void *b" "int c" "size_t len" .Ft void * .Fn memset_explicit "void *b" "int c" "size_t len" .Sh DESCRIPTION The .Fn explicit_memset and .Fn memset_explicit functions write .Fa len bytes of value .Fa c (converted to an unsigned char) to the string .Fa b . They are guaranteed not to be optimized away by the compiler even if .Fa b is no longer used and is about to be freed or go out of scope. .Sh RETURN VALUES The .Fn explicit_memset function returns the original value of .Fa b . .Sh EXAMPLES Create a buffer on the stack for a secret key, use it, and then zero it in memory before throwing it away. d -literal -offset indent void f(void) { uint8_t key[32]; crypto_random(key, sizeof(key)); do_crypto_stuff(key, sizeof(key)); ... explicit_memset(key, 0, sizeof(key)); } .Ed .Sh SEE ALSO .Xr consttime_memequal 3 , .Xr memset 3 .Sh STANDARDS The .Fn memset_explicit function conforms to .St -isoC-2023 . .Sh HISTORY The .Fn explicit_memset function appeared in .Nx 7.0 . The .Fn memset_explicit alias was added in .Nx 11.0 .