Date: Fri, 19 Apr 2019 20:05:48 +0000 (UTC) From: Conrad Meyer <cem@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r346410 - in head: lib/libc/gen share/man/man9 sys/conf sys/libkern sys/sys Message-ID: <201904192005.x3JK5mhm015801@repo.freebsd.org>
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Author: cem Date: Fri Apr 19 20:05:47 2019 New Revision: 346410 URL: https://svnweb.freebsd.org/changeset/base/346410 Log: libkern: Bring in arc4random_uniform(9) from libc 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 Added: head/sys/libkern/arc4random_uniform.c - copied, changed from r346409, head/lib/libc/gen/arc4random_uniform.c Deleted: head/lib/libc/gen/arc4random_uniform.c Modified: head/lib/libc/gen/Makefile.inc head/share/man/man9/Makefile head/share/man/man9/random.9 head/sys/conf/files head/sys/sys/libkern.h Modified: head/lib/libc/gen/Makefile.inc ============================================================================== --- head/lib/libc/gen/Makefile.inc Fri Apr 19 19:45:19 2019 (r346409) +++ head/lib/libc/gen/Makefile.inc Fri Apr 19 20:05:47 2019 (r346410) @@ -3,6 +3,7 @@ # machine-independent gen sources .PATH: ${LIBC_SRCTOP}/${LIBC_ARCH}/gen ${LIBC_SRCTOP}/gen +.PATH: ${SRCTOP}/sys/libkern CONFS= shells Modified: head/share/man/man9/Makefile ============================================================================== --- head/share/man/man9/Makefile Fri Apr 19 19:45:19 2019 (r346409) +++ head/share/man/man9/Makefile Fri Apr 19 20:05:47 2019 (r346410) @@ -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 \ Modified: head/share/man/man9/random.9 ============================================================================== --- head/share/man/man9/random.9 Fri Apr 19 19:45:19 2019 (r346409) +++ head/share/man/man9/random.9 Fri Apr 19 20:05:47 2019 (r346410) @@ -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 @@ -79,6 +81,15 @@ fills 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 Modified: head/sys/conf/files ============================================================================== --- head/sys/conf/files Fri Apr 19 19:45:19 2019 (r346409) +++ head/sys/conf/files Fri Apr 19 20:05:47 2019 (r346410) @@ -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 Copied and modified: head/sys/libkern/arc4random_uniform.c (from r346409, head/lib/libc/gen/arc4random_uniform.c) ============================================================================== --- head/lib/libc/gen/arc4random_uniform.c Fri Apr 19 19:45:19 2019 (r346409, copy source) +++ head/sys/libkern/arc4random_uniform.c Fri Apr 19 20:05:47 2019 (r346410) @@ -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 Modified: head/sys/sys/libkern.h ============================================================================== --- head/sys/sys/libkern.h Fri Apr 19 19:45:19 2019 (r346409) +++ head/sys/sys/libkern.h Fri Apr 19 20:05:47 2019 (r346410) @@ -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 *));
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