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lib/libc/string: add memset_explicit() for compliance with C23

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Patterned after explicit_bzero, visible from C23 onwards.

Reviewed by:	emaste, kevans
Differential Revision:	https://reviews.freebsd.org/D47286
This commit is contained in:
Robert Clausecker 2024-10-25 17:16:27 +02:00
parent 3ef9e138dd
commit 007871c356
5 changed files with 52 additions and 3 deletions
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3
include/string.h
View File

@ -71,6 +71,9 @@ void *(memmove)(void *, const void *, size_t);
void *(mempcpy)(void * __restrict, const void * __restrict, size_t);
#endif
void *(memset)(void *, int, size_t);
#if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2023
void *memset_explicit(void *, int, size_t);
#endif
#if __POSIX_VISIBLE >= 200809
char *(stpcpy)(char * __restrict, const char * __restrict);
char *(stpncpy)(char * __restrict, const char * __restrict, size_t);

4
lib/libc/string/Makefile.inc
View File

@ -11,6 +11,7 @@ MISRCS+=bcmp.c bcopy.c bzero.c explicit_bzero.c \
ffs.c ffsl.c ffsll.c fls.c flsl.c flsll.c \
memccpy.c memchr.c memrchr.c memcmp.c \
memcpy.c memmem.c memmove.c mempcpy.c memset.c memset_s.c \
memset_explicit.c \
stpcpy.c stpncpy.c strcasecmp.c \
strcat.c strcasestr.c strchr.c strchrnul.c strcmp.c strcoll.c strcpy.c\
strcspn.c strdup.c strerror.c strlcat.c strlcpy.c strlen.c strmode.c \
@ -62,7 +63,8 @@ MLINKS+=ffs.3 ffsl.3 \
MLINKS+=index.3 rindex.3
MLINKS+=memchr.3 memrchr.3
MLINKS+=memcpy.3 mempcpy.3
MLINKS+=memset.3 memset_s.3
MLINKS+=memset.3 memset_s.3 \
memset.3 memset_explicit.3
MLINKS+=strcasecmp.3 strncasecmp.3 \
strcasecmp.3 strcasecmp_l.3 \
strcasecmp.3 strncasecmp_l.3

4
lib/libc/string/Symbol.map
View File

@ -116,6 +116,10 @@ FBSD_1.7 {
wmempcpy;
};
FBSD_1.8 {
memset_explicit;
};
FBSDprivate_1.0 {
__strtok_r;
};

18
lib/libc/string/memset.3
View File

@ -29,7 +29,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd August 19, 2018
.Dd October 24, 2024
.Dt MEMSET 3
.Os
.Sh NAME
@ -41,6 +41,8 @@
.In string.h
.Ft void *
.Fn memset "void *dest" "int c" "size_t len"
.Ft void *
.Fn memset_explicit "void *dest" "int c" "size_t len"
.Fd #define __STDC_WANT_LIB_EXT1__ 1
.Ft errno_t
.Fn memset_s "void *dest" "rsize_t destsz" "int c" "rsize_t len"
@ -68,6 +70,13 @@ The behaviour is also undefined if
is an invalid pointer.
.Pp
The
.Fn memset_explicit
function behaves the same as
.Fn memset, but will not be removed by a compiler's dead store
optimization pass, making it useful for clearing sensitive memory
such as a password.
.Pp
The
.Fn memset_s
function behaves the same as
.Fn memset
@ -108,7 +117,9 @@ before
.Sh RETURN VALUES
The
.Fn memset
function returns its first argument.
and
.Fn memset_explicit
functions return their first argument.
The
.Fn memset_s
function returns zero on success, non-zero on error.
@ -128,3 +139,6 @@ conforms to
conforms to
.St -isoC-2011
K.3.7.4.1.
.Fn memset_explicit
conforms to
.St -isoC-2024 .

26
lib/libc/string/memset_explicit.c Normal file
View File

@ -0,0 +1,26 @@
/*-
* SPDF-License-Identifier: BSD-2-Clause
*
* Copyright (c) 2024 Robert Clausecker <fuz@FreeBSD.org>
*/
#include <string.h>
__attribute__((weak)) void __memset_explicit_hook(void *, int, size_t);
__attribute__((weak)) void
__memset_explicit_hook(void *buf, int ch, size_t len)
{
(void)buf;
(void)ch;
(void)len;
}
void *
memset_explicit(void *buf, int ch, size_t len)
{
memset(buf, ch, len);
__memset_explicit_hook(buf, ch, len);
return (buf);
}