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.

ChangeLog

@@ -1,5 +1,13 @@
 2019-03-22  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
+	* 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/libc-internal.h (__get_clockfreq): Remove prototype.
 	* rt/Makefile (clock-routines): Remove get_clockfreq.
 	* rt/get_clockfreq.c: Remove file.

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
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _RANDOM_BITS_H
+# define _RANDOM_BITS_H
+
+#include <time.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. */
+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

resolv/res_mkquery.c

@@ -82,6 +82,7 @@
  * SOFTWARE.
  */
 
+#include <stdint.h>
 #include <sys/types.h>
 #include <sys/param.h>
 #include <netinet/in.h>
@@ -92,12 +93,7 @@
 #include <string.h>
 #include <sys/time.h>
 #include <shlib-compat.h>
-
+#include <random-bits.h>
-#include <hp-timing.h>
-#include <stdint.h>
-#if HP_TIMING_AVAIL
-# define RANDOM_BITS(Var) { uint64_t v64; HP_TIMING_NOW (v64); Var = v64; }
-#endif
 
 int
 __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
@@ -120,16 +116,7 @@ __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
   /* We randomize the IDs every time.  The old code just incremented
      by one after the initial randomization which still predictable if
      the application does multiple requests.  */
-  int randombits;
+  hp->id = random_bits ();
-#ifdef RANDOM_BITS
-  RANDOM_BITS (randombits);
-#else
-  struct timeval tv;
-  __gettimeofday (&tv, NULL);
-  randombits = (tv.tv_sec << 8) ^ tv.tv_usec;
-#endif
-
-  hp->id = randombits;
   hp->opcode = op;
   hp->rd = (ctx->resp->options & RES_RECURSE) != 0;
   hp->rcode = NOERROR;

resolv/res_send.c

@@ -109,7 +109,7 @@
 #include <unistd.h>
 #include <kernel-features.h>
 #include <libc-diag.h>
-#include <hp-timing.h>
+#include <random-bits.h>
 
 #if PACKETSZ > 65536
 #define MAXPACKET       PACKETSZ
@@ -309,15 +309,7 @@ nameserver_offset (struct __res_state *statp)
   if ((offset & 1) == 0)
     {
       /* Initialization is required.  */
-#if HP_TIMING_AVAIL
+      offset = random_bits ();
-      uint64_t ticks;
-      HP_TIMING_NOW (ticks);
-      offset = ticks;
-#else
-      struct timeval tv;
-      __gettimeofday (&tv, NULL);
-      offset = ((tv.tv_sec << 8) ^ tv.tv_usec);
-#endif
       /* The lowest bit is the most random.  Preserve it.  */
       offset <<= 1;
 

sysdeps/posix/tempname.c

@@ -71,22 +71,15 @@
 #endif
 
 #ifdef _LIBC
-# include <hp-timing.h>
+# include <random-bits.h>
-# if HP_TIMING_AVAIL
+# define RANDOM_BITS(Var) ((Var) = random_bits ())
-#  define RANDOM_BITS(Var) \
+# else
-  if (__glibc_unlikely (value == UINT64_C (0)))				      \
+# define RANDOM_BITS(Var) \
-    {									      \
+    {                                                                         \
-      /* If this is the first time this function is used initialize	      \
+      struct timeval tv;                                                      \
-	 the variable we accumulate the value in to some somewhat	      \
+      __gettimeofday (&tv, NULL);                                             \
-	 random value.  If we'd not do this programs at startup time	      \
+      (Var) = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
-	 might have a reduced set of possible names, at least on slow	      \
+    }
-	 machines.  */							      \
-      struct timeval tv;						      \
-      __gettimeofday (&tv, NULL);					      \
-      value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;		      \
-    }									      \
-  HP_TIMING_NOW (Var)
-# endif
 #endif
 
 /* Use the widest available unsigned type if uint64_t is not
@@ -193,8 +186,7 @@ __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
 {
   int len;
   char *XXXXXX;
-  static uint64_t value;
+  uint64_t value;
-  uint64_t random_time_bits;
   unsigned int count;
   int fd = -1;
   int save_errno = errno;
@@ -227,16 +219,8 @@ __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
   XXXXXX = &tmpl[len - 6 - suffixlen];
 
   /* Get some more or less random data.  */
-#ifdef RANDOM_BITS
+  RANDOM_BITS (value);
-  RANDOM_BITS (random_time_bits);
+  value ^= (uint64_t)__getpid () << 32;
-#else
-  {
-    struct timeval tv;
-    __gettimeofday (&tv, NULL);
-    random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
-  }
-#endif
-  value += random_time_bits ^ __getpid ();
 
   for (count = 0; count < attempts; value += 7777, ++count)
     {