From 359653aaacad463d916323f03c0ac3c47405aafa Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Wed, 16 Jan 2019 18:10:56 +0000
Subject: [PATCH] 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.

note that this patch is just parts of the origin one to adapt glibc-2.28 
	

---
 resolv/res_mkquery.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
index 213abeef..7ba40640 100644
--- a/resolv/res_mkquery.c
+++ b/resolv/res_mkquery.c
@@ -95,6 +95,7 @@
 
 #include <hp-timing.h>
 #include <stdint.h>
+#include <time.h>
 #if HP_TIMING_AVAIL
 # define RANDOM_BITS(Var) { uint64_t v64; HP_TIMING_NOW (v64); Var = v64; }
 #endif
@@ -124,9 +125,12 @@ __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
 #ifdef RANDOM_BITS
   RANDOM_BITS (randombits);
 #else
-  struct timeval tv;
-  __gettimeofday (&tv, NULL);
-  randombits = (tv.tv_sec << 8) ^ tv.tv_usec;
+  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);
+  randombits = ret;
 #endif
 
   hp->id = randombits;
-- 
2.19.1