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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.
This commit is contained in:
Adhemerval Zanella
parent
6e8ba7fd57
commit
359653aaac
@ -1,5 +1,13 @@
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2019-03-22 Adhemerval Zanella <adhemerval.zanella@linaro.org>
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* include/random-bits.h: New file.
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* resolv/res_mkquery.c [HP_TIMING_AVAIL] (RANDOM_BITS,
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(__res_context_mkquery): Remove usage hp-timing usage and replace with
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random_bits.
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* resolv/res_send.c [HP_TIMING_AVAIL] (nameserver_offset): Likewise.
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* sysdeps/posix/tempname.c [HP_TIMING_AVAIL] (__gen_tempname):
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Likewise.
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* include/libc-internal.h (__get_clockfreq): Remove prototype.
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* rt/Makefile (clock-routines): Remove get_clockfreq.
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* rt/get_clockfreq.c: Remove file.
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41
include/random-bits.h
Normal file
41
include/random-bits.h
Normal file
@ -0,0 +1,41 @@
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/* Fast pseudo-random bits based on clock_gettime.
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Copyright (C) 2019 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _RANDOM_BITS_H
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# define _RANDOM_BITS_H
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#include <time.h>
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#include <stdint.h>
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/* Provides fast pseudo-random bits through clock_gettime. It has unspecified
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starting time, nano-second accuracy, its randomness is significantly better
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than gettimeofday, and for mostly architectures it is implemented through
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vDSO instead of a syscall. Since the source is a system clock, the upper
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bits will have less entropy. */
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static inline uint32_t
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random_bits (void)
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{
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struct timespec tv;
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__clock_gettime (CLOCK_MONOTONIC, &tv);
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/* Shuffle the lower bits to minimize the clock bias. */
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uint32_t ret = tv.tv_nsec ^ tv.tv_sec;
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ret ^= (ret << 24) | (ret >> 8);
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return ret;
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}
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#endif
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@ -82,6 +82,7 @@
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* SOFTWARE.
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*/
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#include <stdint.h>
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#include <sys/types.h>
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#include <sys/param.h>
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#include <netinet/in.h>
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@ -92,12 +93,7 @@
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#include <string.h>
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#include <sys/time.h>
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#include <shlib-compat.h>
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#include <hp-timing.h>
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#include <stdint.h>
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#if HP_TIMING_AVAIL
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# define RANDOM_BITS(Var) { uint64_t v64; HP_TIMING_NOW (v64); Var = v64; }
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#endif
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#include <random-bits.h>
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int
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__res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
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@ -120,16 +116,7 @@ __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
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/* We randomize the IDs every time. The old code just incremented
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by one after the initial randomization which still predictable if
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the application does multiple requests. */
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int randombits;
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#ifdef RANDOM_BITS
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RANDOM_BITS (randombits);
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#else
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struct timeval tv;
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__gettimeofday (&tv, NULL);
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randombits = (tv.tv_sec << 8) ^ tv.tv_usec;
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#endif
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hp->id = randombits;
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hp->id = random_bits ();
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hp->opcode = op;
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hp->rd = (ctx->resp->options & RES_RECURSE) != 0;
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hp->rcode = NOERROR;
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@ -109,7 +109,7 @@
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#include <unistd.h>
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#include <kernel-features.h>
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#include <libc-diag.h>
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#include <hp-timing.h>
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#include <random-bits.h>
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#if PACKETSZ > 65536
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#define MAXPACKET PACKETSZ
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@ -309,15 +309,7 @@ nameserver_offset (struct __res_state *statp)
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if ((offset & 1) == 0)
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{
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/* Initialization is required. */
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#if HP_TIMING_AVAIL
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uint64_t ticks;
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HP_TIMING_NOW (ticks);
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offset = ticks;
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#else
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struct timeval tv;
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__gettimeofday (&tv, NULL);
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offset = ((tv.tv_sec << 8) ^ tv.tv_usec);
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#endif
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offset = random_bits ();
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/* The lowest bit is the most random. Preserve it. */
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offset <<= 1;
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@ -71,22 +71,15 @@
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#endif
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#ifdef _LIBC
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# include <hp-timing.h>
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# if HP_TIMING_AVAIL
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# define RANDOM_BITS(Var) \
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if (__glibc_unlikely (value == UINT64_C (0))) \
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{ \
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/* If this is the first time this function is used initialize \
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the variable we accumulate the value in to some somewhat \
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random value. If we'd not do this programs at startup time \
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might have a reduced set of possible names, at least on slow \
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machines. */ \
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struct timeval tv; \
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__gettimeofday (&tv, NULL); \
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value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; \
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} \
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HP_TIMING_NOW (Var)
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# endif
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# include <random-bits.h>
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# define RANDOM_BITS(Var) ((Var) = random_bits ())
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# else
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# define RANDOM_BITS(Var) \
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{ \
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struct timeval tv; \
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__gettimeofday (&tv, NULL); \
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(Var) = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; \
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}
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#endif
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/* Use the widest available unsigned type if uint64_t is not
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@ -193,8 +186,7 @@ __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
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{
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int len;
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char *XXXXXX;
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static uint64_t value;
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uint64_t random_time_bits;
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uint64_t value;
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unsigned int count;
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int fd = -1;
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int save_errno = errno;
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@ -227,16 +219,8 @@ __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
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XXXXXX = &tmpl[len - 6 - suffixlen];
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/* Get some more or less random data. */
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#ifdef RANDOM_BITS
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RANDOM_BITS (random_time_bits);
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#else
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{
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struct timeval tv;
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__gettimeofday (&tv, NULL);
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random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
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}
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#endif
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value += random_time_bits ^ __getpid ();
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RANDOM_BITS (value);
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value ^= (uint64_t)__getpid () << 32;
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for (count = 0; count < attempts; value += 7777, ++count)
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{
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