lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <1444169140-4938-2-git-send-email-andi@firstfloor.org>
Date:	Tue,  6 Oct 2015 15:05:39 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	tytso@....edu
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 2/3] random: Make input to output pool balancing per cpu

From: Andi Kleen <ak@...ux.intel.com>

The load balancing from input pool to output pools was
essentially unlocked. Before it didn't matter much because
there were only two choices (blocking and non blocking).

But now with the distributed non blocking pools we have
a lot more pools, and unlocked access of the counters
may systematically deprive some nodes from their deserved
entropy.

Turn the round-robin state into per CPU variables
to avoid any possibility of races. This code already
runs with preemption disabled.

v2: Check for non initialized pools.
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 drivers/char/random.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index e7e02c0..a395f783 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -774,15 +774,20 @@ retry:
 		if (entropy_bits > random_write_wakeup_bits &&
 		    r->initialized &&
 		    r->entropy_total >= 2*random_read_wakeup_bits) {
-			static struct entropy_store *last = &blocking_pool;
-			static int next_pool = -1;
-			struct entropy_store *other = &blocking_pool;
+			static DEFINE_PER_CPU(struct entropy_store *, lastp) =
+				&blocking_pool;
+			static DEFINE_PER_CPU(int, next_pool);
+			struct entropy_store *other = &blocking_pool, *last;
+			int np;
 
 			/* -1: use blocking pool, 0<=max_node: node nb pool */
-			if (next_pool > -1)
-				other = nonblocking_node_pool[next_pool];
-			if (++next_pool >= num_possible_nodes())
-				next_pool = -1;
+			np = __this_cpu_read(next_pool);
+			if (np > -1 && nonblocking_node_pool)
+				other = nonblocking_node_pool[np];
+			if (++np >= num_possible_nodes())
+				np = -1;
+			__this_cpu_write(next_pool, np);
+			last = __this_cpu_read(lastp);
 			if (other->entropy_count <=
 			    3 * other->poolinfo->poolfracbits / 4)
 				last = other;
@@ -791,6 +796,7 @@ retry:
 				schedule_work(&last->push_work);
 				r->entropy_total = 0;
 			}
+			__this_cpu_write(lastp, last);
 		}
 	}
 }
-- 
2.4.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ