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libkern: Bring in arc4random_uniform(9) from libc

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It is a useful arc4random wrapper in the kernel for much the same reasons as
in userspace.  Move the source to libkern (because kernel build is
restricted to sys/, but userspace can include any file it likes) and build
kernel and libc versions from the same source file.

Copy the documentation from arc4random_uniform(3) to the section 9 page.

While here, add missing arc4random_buf(9) symlink.

Sponsored by:	Dell EMC Isilon
This commit is contained in:
Conrad Meyer 2019-04-19 20:05:47 +00:00
parent 16b07b25c4
commit 7deb4b1964
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=346410
6 changed files with 21 additions and 1 deletions
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1
lib/libc/gen/Makefile.inc
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@ -3,6 +3,7 @@
# machine-independent gen sources
.PATH: ${LIBC_SRCTOP}/${LIBC_ARCH}/gen ${LIBC_SRCTOP}/gen
.PATH: ${SRCTOP}/sys/libkern
CONFS= shells

2
share/man/man9/Makefile
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@ -1668,6 +1668,8 @@ MLINKS+=psignal.9 gsignal.9 \
psignal.9 tdsignal.9
MLINKS+=random.9 arc4rand.9 \
random.9 arc4random.9 \
random.9 arc4random_buf.9 \
random.9 arc4random_uniform.9 \
random.9 is_random_seeded.9 \
random.9 read_random.9 \
random.9 read_random_uio.9 \

13
share/man/man9/random.9
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@ -26,7 +26,7 @@
.\"
.\" $FreeBSD$
.\" "
.Dd April 16, 2019
.Dd April 19, 2019
.Dt RANDOM 9
.Os
.Sh NAME
@ -45,6 +45,8 @@
.Fn arc4random "void"
.Ft void
.Fn arc4random_buf "void *ptr" "size_t len"
.Ft uint32_t
.Fn arc4random_uniform "uint32_t upper_bound"
.Ft void
.Fn arc4rand "void *ptr" "u_int length" "int reseed"
.Pp
@ -80,6 +82,15 @@ with
.Fa len
bytes of random data.
.Pp
.Fn arc4random_uniform
will return a single 32-bit value, uniformly distributed but less than
.Fa upper_bound .
This is recommended over constructions like
.Dq Li arc4random() % upper_bound
as it avoids "modulo bias" when the upper bound is not a power of two.
In the worst case, this function may consume multiple iterations
to ensure uniformity.
.Pp
The
.Fn arc4rand
CSPRNG

1
sys/conf/files
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@ -3985,6 +3985,7 @@ kgssapi/gsstest.c optional kgssapi_debug
# the file should be moved to conf/files.<arch> from here.
#
libkern/arc4random.c standard
libkern/arc4random_uniform.c standard
crypto/chacha20/chacha.c standard
libkern/asprintf.c standard
libkern/bcd.c standard

4
lib/libc/gen/arc4random_uniform.c → sys/libkern/arc4random_uniform.c
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@ -19,7 +19,11 @@
*/
#include <sys/types.h>
#ifdef _KERNEL
#include <sys/libkern.h>
#else
#include <stdlib.h>
#endif
/*
* Calculate a uniformly distributed random number less than upper_bound

1
sys/sys/libkern.h
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@ -128,6 +128,7 @@ struct malloc_type;
uint32_t arc4random(void);
void arc4random_buf(void *, size_t);
void arc4rand(void *, u_int, int);
uint32_t arc4random_uniform(uint32_t);
int timingsafe_bcmp(const void *, const void *, size_t);
void *bsearch(const void *, const void *, size_t,
size_t, int (*)(const void *, const void *));