From: Noah Goldstein <goldstein.w.n@gmail.com>
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 [thread overview]
Message-ID: <20220328220936.2724834-1-goldstein.w.n@gmail.com> (raw)
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/<arch>/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 <time.h>
-#include <stdint.h>
+# include <random-bits-entropy.h>
+# include <stdint.h>
-/* 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <stdint.h>
+#include <time.h>
+
+/* 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;
+}
--
2.25.1
next reply other threads:[~2022-03-28 22:09 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-28 22:09 Noah Goldstein [this message]
2022-03-28 22:09 ` [PATCH v1 2/2] x86: Use rdtsc for generating entropy for random_bits Noah Goldstein
2022-03-29 19:51 ` [PATCH v1 1/2] random-bits: Factor out entropy generating function Adhemerval Zanella
2022-03-29 19:56 ` Noah Goldstein
2022-03-29 20:04 ` Noah Goldstein
2022-03-29 20:14 ` H.J. Lu
2022-03-29 20:44 ` Adhemerval Zanella
2022-03-29 20:52 ` Noah Goldstein
2022-03-29 20:37 ` Adhemerval Zanella
2022-03-29 20:44 ` Noah Goldstein
2022-03-30 15:37 ` Adhemerval Zanella
2022-03-30 16:30 ` Noah Goldstein
2022-03-30 19:38 ` Cristian Rodríguez
2022-03-31 4:45 ` Jason A. Donenfeld
2022-03-31 10:08 ` Cristian Rodríguez
2022-03-31 11:17 ` Adhemerval Zanella
2022-03-31 11:25 ` Cristian Rodríguez
2022-03-31 11:48 ` Adhemerval Zanella
2022-03-31 12:14 ` Cristian Rodríguez
2022-03-31 13:12 ` Yann Droneaud
2022-03-31 15:31 ` Jason A. Donenfeld
2022-03-31 18:16 ` Noah Goldstein
2022-03-31 21:57 ` Cristian Rodríguez
2022-03-31 22:33 ` Noah Goldstein
2022-03-31 22:51 ` Jason A. Donenfeld
2022-03-31 23:05 ` Noah Goldstein
2022-03-31 23:25 ` Jason A. Donenfeld
2022-04-01 18:01 ` Cristian Rodríguez
2022-04-04 17:42 ` Adhemerval Zanella
2022-04-04 18:23 ` Noah Goldstein
2022-04-04 18:38 ` Adhemerval Zanella
2022-04-04 18:52 ` Noah Goldstein
2022-04-04 19:20 ` Adhemerval Zanella
2022-04-04 19:48 ` Noah Goldstein
2022-04-04 19:57 ` Adhemerval Zanella
2022-04-04 14:51 ` Florian Weimer
2022-04-04 14:54 ` Jason A. Donenfeld
2022-04-04 15:00 ` Florian Weimer
2022-04-04 16:51 ` Noah Goldstein
2022-04-04 17:22 ` Adhemerval Zanella
2022-04-04 18:32 ` Jason A. Donenfeld
2022-04-04 19:16 ` Noah Goldstein
2022-04-05 0:10 ` Cristian Rodríguez
2022-04-05 0:18 ` Jason A. Donenfeld
2022-04-05 13:45 ` Cristian Rodríguez
2022-04-05 9:22 ` Florian Weimer
2022-04-04 18:28 ` Jason A. Donenfeld
2022-04-05 9:20 ` Florian Weimer
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