Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753988Ab3JBOgO (ORCPT ); Wed, 2 Oct 2013 10:36:14 -0400 Received: from cantor2.suse.de ([195.135.220.15]:49513 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753281Ab3JBOgL convert rfc822-to-8bit (ORCPT ); Wed, 2 Oct 2013 10:36:11 -0400 Subject: Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on some powernv systems Mime-Version: 1.0 (Apple Message framework v1278) Content-Type: text/plain; charset=US-ASCII From: Alexander Graf In-Reply-To: <524C2EAE.7090209@redhat.com> Date: Wed, 2 Oct 2013 16:36:05 +0200 Cc: Michael Ellerman , Gleb Natapov , Benjamin Herrenschmidt , Paul Mackerras , linux-kernel@vger.kernel.org, mpm@selenic.com, herbert@gondor.hengli.com.au, linuxppc-dev@ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, tytso@mit.edu Content-Transfer-Encoding: 7BIT Message-Id: References: <5243F933.7000907@redhat.com> <20131001083426.GB27484@concordia> <20131001083908.GA17294@redhat.com> <1380620338.645.22.camel@pasglop> <524AAFAA.3010801@redhat.com> <20131002050940.GA25363@drongo> <524BDD73.3020106@redhat.com> <1380704789.645.57.camel@pasglop> <668E4650-BC22-4CBF-A282-E7875DF29DB6@suse.de> <3CBF5732-E7EE-4C96-8132-6D7B77270DAF@suse.de> <20131002100224.GF17294@redhat.com> <1380722275.12149.28.camel@concordia> <029A8D6C-C23C-42B2-8C26-D76B59E2C9DD@suse.de> <524C2EAE.7090209@redhat.com> To: Paolo Bonzini X-Mailer: Apple Mail (2.1278) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1230 Lines: 28 On 02.10.2013, at 16:33, Paolo Bonzini wrote: > Il 02/10/2013 16:08, Alexander Graf ha scritto: >>> The hwrng is accessible by host userspace via /dev/mem. >> >> A guest should live on the same permission level as a user space >> application. If you run QEMU as UID 1000 without access to /dev/mem, why >> should the guest suddenly be able to directly access a memory location >> (MMIO) it couldn't access directly through a normal user space interface. >> >> It's basically a layering violation. > > With Michael's earlier patch in this series, the hwrng is accessible by > host userspace via /dev/hwrng, no? Yes, but there's not token from user space that gets passed into the kernel to check whether access is ok or not. So while QEMU may not have permission to open /dev/hwrng it could spawn a guest that opens it, drains all entropy out of it and thus stall other processes which try to fetch entropy, no? Maybe I haven't fully grasped the interface yet though :). Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/