[dpdk-dev] [PATCH v4 3/5] eal: improve entropy for initial PRNG seed

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

Replace the use of rte_get_timer_cycles() with getentropy() for
seeding the pseudo-random number generator. getentropy() provides a
more truly random value.

getentropy() requires glibc 2.25 and Linux kernel 3.17. In case
getentropy() is not found at compile time, or the relevant syscall
fails in runtime, the rdseed machine instruction will be used as a
fallback.

rdseed is only available on x86 (Broadwell or later). In case it is
not present, rte_get_timer_cycles() will be used as a second fallback.

On non-Meson builds, getentropy() will not be used.

Suggested-by: Bruce Richardson <bruce.richardson@intel.com>
Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
---
 lib/librte_eal/common/rte_random.c | 36 +++++++++++++++++++++++++++++-
 lib/librte_eal/meson.build         |  3 +++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/lib/librte_eal/common/rte_random.c b/lib/librte_eal/common/rte_random.c
index 4d3cf5226..e53d96d18 100644
--- a/lib/librte_eal/common/rte_random.c
+++ b/lib/librte_eal/common/rte_random.c
@@ -2,7 +2,11 @@
  * Copyright(c) 2019 Ericsson AB
  */
 
+#ifdef RTE_MACHINE_CPUFLAG_RDSEED
+#include <x86intrin.h>
+#endif
 #include <stdlib.h>
+#include <unistd.h>
 
 #include <rte_branch_prediction.h>
 #include <rte_cycles.h>
@@ -133,7 +137,37 @@ rte_rand(void)
 	return __rte_rand_lfsr258(state);
 }
 
+static uint64_t
+__rte_random_initial_seed(void)
+{
+#ifdef RTE_LIBEAL_USE_GETENTROPY
+	int ge_rc;
+	uint64_t ge_seed;
+
+	ge_rc = getentropy(&ge_seed, sizeof(ge_seed));
+
+	if (ge_rc == 0)
+		return ge_seed;
+#endif
+#ifdef RTE_MACHINE_CPUFLAG_RDSEED
+	unsigned int rdseed_rc;
+	unsigned long long rdseed_seed;
+
+	/* first fallback: rdseed instruction, if available */
+	rdseed_rc = _rdseed64_step(&rdseed_seed);
+
+	if (rdseed_rc == 1)
+		return (uint64_t)rdseed_seed;
+#endif
+	/* second fallback: seed using rdtsc */
+	return rte_get_timer_cycles();
+}
+
 RTE_INIT(rte_rand_init)
 {
-	rte_srand(rte_get_timer_cycles());
+	uint64_t seed;
+
+	seed = __rte_random_initial_seed();
+
+	rte_srand(seed);
 }
diff --git a/lib/librte_eal/meson.build b/lib/librte_eal/meson.build
index fa36b20e0..ccd5b85b8 100644
--- a/lib/librte_eal/meson.build
+++ b/lib/librte_eal/meson.build
@@ -18,6 +18,9 @@ deps += 'kvargs'
 if dpdk_conf.has('RTE_USE_LIBBSD')
 	ext_deps += libbsd
 endif
+if cc.has_function('getentropy', prefix : '#include <unistd.h>')
+	cflags += '-DRTE_LIBEAL_USE_GETENTROPY'
+endif
 sources = common_sources + env_sources
 objs = common_objs + env_objs
 headers = common_headers + env_headers
-- 
2.17.1