From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752392AbaCQXhD (ORCPT ); Mon, 17 Mar 2014 19:37:03 -0400 Received: from mga11.intel.com ([192.55.52.93]:48988 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751706AbaCQXgt (ORCPT ); Mon, 17 Mar 2014 19:36:49 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,673,1389772800"; d="scan'208";a="500757083" From: "H. Peter Anvin" To: "Ted Ts'o" , Linus Torvalds , Ingo Molnar , Thomas Gleixner Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Linux Kernel Mailing List , "H. Peter Anvin" Subject: [PATCH v2 3/4] random: If we have arch_get_random_seed*(), try it before blocking Date: Mon, 17 Mar 2014 16:36:29 -0700 Message-Id: <1395099390-807-4-git-send-email-hpa@linux.intel.com> X-Mailer: git-send-email 1.8.5.3 In-Reply-To: <1395099390-807-1-git-send-email-hpa@linux.intel.com> References: <1395099390-807-1-git-send-email-hpa@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we have arch_get_random_seed*(), try to use it for emergency refill of the entropy pool before giving up and blocking on /dev/random. It may or may not work in the moment, but if it does work, it will give the user better service than blocking will. Reviewed-by: Ingo Molnar Signed-off-by: H. Peter Anvin --- drivers/char/random.c | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index a4bea77..c35cee2 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1294,6 +1294,34 @@ void rand_initialize_disk(struct gendisk *disk) } #endif +/* + * Attempt an emergency refill using arch_get_random_seed_long(). + * + * As with add_interrupt_randomness() be paranoid and only + * credit the output as 50% entropic. + */ +static int arch_random_refill(void) +{ + const unsigned int nlongs = 64; /* Arbitrary number */ + unsigned int n = 0; + unsigned int i; + unsigned long buf[nlongs]; + + for (i = 0; i < nlongs; i++) { + if (arch_get_random_seed_long(&buf[n])) + n++; + } + + if (n) { + unsigned int rand_bytes = n * sizeof(unsigned long); + + mix_pool_bytes(&input_pool, buf, rand_bytes, NULL); + credit_entropy_bits(&input_pool, rand_bytes*4); + } + + return n; +} + static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { @@ -1312,8 +1340,13 @@ random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) ENTROPY_BITS(&input_pool)); if (n > 0) return n; + /* Pool is (near) empty. Maybe wait and retry. */ + /* First try an emergency refill */ + if (arch_random_refill()) + continue; + if (file->f_flags & O_NONBLOCK) return -EAGAIN; -- 1.8.5.3