From 359653aaacad463d916323f03c0ac3c47405aafa Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Wed, 16 Jan 2019 18:10:56 +0000 Subject: Do not use HP_TIMING_NOW for random bits This patch removes the HP_TIMING_BITS usage for fast random bits and replace with clock_gettime (CLOCK_MONOTONIC). It has unspecified starting time and nano-second accuracy, so its randomness is significantly better than gettimeofday. Althoug it should incur in more overhead (specially for architecture that support hp-timing), the symbol is also common implemented as a vDSO. Checked on aarch64-linux-gnu, x86_64-linux-gnu, and i686-linux-gnu. I also checked on a i686-gnu build. * include/random-bits.h: New file. * resolv/res_mkquery.c [HP_TIMING_AVAIL] (RANDOM_BITS, (__res_context_mkquery): Remove usage hp-timing usage and replace with random_bits. * resolv/res_send.c [HP_TIMING_AVAIL] (nameserver_offset): Likewise. * sysdeps/posix/tempname.c [HP_TIMING_AVAIL] (__gen_tempname): Likewise. --- include/random-bits.h | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) create mode 100644 include/random-bits.h (limited to 'include') diff --git a/include/random-bits.h b/include/random-bits.h new file mode 100644 index 0000000000..a0651a5a34 --- /dev/null +++ b/include/random-bits.h @@ -0,0 +1,41 @@ +/* Fast pseudo-random bits based on clock_gettime. + Copyright (C) 2019 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#ifndef _RANDOM_BITS_H +# define _RANDOM_BITS_H + +#include +#include + +/* Provides fast pseudo-random bits through clock_gettime. It has unspecified + starting time, nano-second accuracy, its randomness is significantly better + than gettimeofday, and for mostly architectures it is implemented through + vDSO instead of a syscall. Since the source is a system clock, the upper + bits will have less entropy. */ +static inline uint32_t +random_bits (void) +{ + struct timespec tv; + __clock_gettime (CLOCK_MONOTONIC, &tv); + /* Shuffle the lower bits to minimize the clock bias. */ + uint32_t ret = tv.tv_nsec ^ tv.tv_sec; + ret ^= (ret << 24) | (ret >> 8); + return ret; +} + +#endif -- cgit v1.2.3