From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3E41C28CC0 for ; Wed, 29 May 2019 15:57:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C242723C5A for ; Wed, 29 May 2019 15:57:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726806AbfE2P5L convert rfc822-to-8bit (ORCPT ); Wed, 29 May 2019 11:57:11 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:58474 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726330AbfE2P5L (ORCPT ); Wed, 29 May 2019 11:57:11 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-44-DsTTXp3NMOGiB7xDBxoT-w-1; Wed, 29 May 2019 16:57:08 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 29 May 2019 16:57:07 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Wed, 29 May 2019 16:57:07 +0100 From: David Laight To: 'Neil Horman' CC: "linux-kernel@vger.kernel.org" , Steve Grubb , Theodore Ts'o , Arnd Bergmann , Greg Kroah-Hartman Subject: RE: [PATCH] Fix xoring of arch_get_random_long into crng->state array Thread-Topic: [PATCH] Fix xoring of arch_get_random_long into crng->state array Thread-Index: AQHVFiSGW6uE5jAIekyknyRep1UK46aCHqcQgAARLgCAABHlkA== Date: Wed, 29 May 2019 15:57:07 +0000 Message-ID: References: <20190402220025.14499-1-nhorman@tuxdriver.com> <20190529134200.GA31099@hmswarspite.think-freely.org> <20190529155156.GB31099@hmswarspite.think-freely.org> In-Reply-To: <20190529155156.GB31099@hmswarspite.think-freely.org> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: DsTTXp3NMOGiB7xDBxoT-w-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Neil Horman [mailto:nhorman@tuxdriver.com] > Sent: 29 May 2019 16:52 > On Wed, May 29, 2019 at 01:51:24PM +0000, David Laight wrote: > > From: Neil Horman > > > Sent: 29 May 2019 14:42 > > > On Tue, Apr 02, 2019 at 06:00:25PM -0400, Neil Horman wrote: > > > > When _crng_extract is called, any arch that has a registered > > > > arch_get_random_long method, attempts to mix an unsigned long value into > > > > the crng->state buffer, it only mixes in 32 of the 64 bits available, > > > > because the state buffer is an array of u32 values, even though 2 u32 > > > > are expected to be filled (owing to the fact that it expects indexes 14 > > > > and 15 to be filled). > > > > > > > > Bring the expected behavior into alignment by casting index 14 to an > > > > unsignled long pointer, and xoring that in instead. > > ... > > > > diff --git a/drivers/char/random.c b/drivers/char/random.c > > > > index 38c6d1af6d1c..8178618458ac 100644 > > > > --- a/drivers/char/random.c > > > > +++ b/drivers/char/random.c > > > > @@ -975,14 +975,16 @@ static void _extract_crng(struct crng_state *crng, > > > > __u8 out[CHACHA_BLOCK_SIZE]) > > > > { > > > > unsigned long v, flags; > > > > - > > > > + unsigned long *archrnd; > > > > if (crng_ready() && > > > > (time_after(crng_global_init_time, crng->init_time) || > > > > time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL))) > > > > crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL); > > > > spin_lock_irqsave(&crng->lock, flags); > > > > - if (arch_get_random_long(&v)) > > > > - crng->state[14] ^= v; > > > > + if (arch_get_random_long(&v)) { > > > > + archrnd = (unsigned long *)&crng->state[14]; > > > > + *archrnd ^= v; > > > > + } > > > > Isn't that likely to generate a misaligned memory access? > > > I'm not quite sure how it would, crng->state is an array of _u32's, and so every > even element should be on a 64 bit boundary. Only if the first item is aligned.... Add a u32 before it and you'll probably flip the alignment. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)