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[76.191.17.161]) by smtp.googlemail.com with ESMTPSA id y74-20020a6bc84d000000b00645dfdd8a4csm8622442iof.38.2022.03.28.15.09.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Mar 2022 15:09:45 -0700 (PDT) To: libc-alpha@sourceware.org Subject: [PATCH v1 1/2] random-bits: Factor out entropy generating function Date: Mon, 28 Mar 2022 17:09:35 -0500 Message-Id: <20220328220936.2724834-1-goldstein.w.n@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Spam-Status: No, score=-12.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Noah Goldstein via Libc-alpha From: Noah Goldstein Reply-To: Noah Goldstein Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" On some architectures `clock_gettime` is undesirable as it may use a syscall or there may be a faster alternative. Future architecture specific functions can be added in sysdeps//random-bits-entropy.h to provide a version of 'random_bits_entropy' that doesn't use 'clock_gettime'. --- include/random-bits.h | 16 ++++++-------- sysdeps/generic/random-bits-entropy.h | 31 +++++++++++++++++++++++++++ 2 files changed, 37 insertions(+), 10 deletions(-) create mode 100644 sysdeps/generic/random-bits-entropy.h diff --git a/include/random-bits.h b/include/random-bits.h index 17665b479a..016b87576c 100644 --- a/include/random-bits.h +++ b/include/random-bits.h @@ -19,21 +19,17 @@ #ifndef _RANDOM_BITS_H # define _RANDOM_BITS_H -#include -#include +# 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. */ +/* Provides fast pseudo-random bits through architecture specific + random_bits_entropy. Expectation is source is some timing function so + the upper bits have less entropy. */ static inline uint32_t random_bits (void) { - struct __timespec64 tv; - __clock_gettime64 (CLOCK_MONOTONIC, &tv); + uint32_t ret = random_bits_entropy (); /* 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; } diff --git a/sysdeps/generic/random-bits-entropy.h b/sysdeps/generic/random-bits-entropy.h new file mode 100644 index 0000000000..53290c7f7a --- /dev/null +++ b/sysdeps/generic/random-bits-entropy.h @@ -0,0 +1,31 @@ +/* Fast function for generating entropy of random_bits. + Copyright (C) 2022 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 + . */ + +#include +#include + +/* Generically use 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. */ +static inline uint32_t +random_bits_entropy (void) +{ + struct __timespec64 tv; + __clock_gettime64 (CLOCK_MONOTONIC, &tv); + return tv.tv_nsec ^ tv.tv_sec; +}