From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga12.intel.com ([192.55.52.136]:37683 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726844AbeIRCsW (ORCPT ); Mon, 17 Sep 2018 22:48:22 -0400 Date: Tue, 18 Sep 2018 00:19:00 +0300 From: Jarkko Sakkinen To: Boris Ostrovsky Cc: peterhuewe@gmx.de, jgg@ziepe.ca, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, jgross@suse.com, dunlapg@umich.edu, "Dr. Greg Wettstein" , "Dr . Greg Wettstein" , stable@vger.kernel.org Subject: Re: [PATCH v2] tpm: Restore functionality to xen vtpm driver. Message-ID: <20180917211900.GD6716@linux.intel.com> References: <20180913212551.2435-1-boris.ostrovsky@oracle.com> <20180916192510.GF7473@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-integrity-owner@vger.kernel.org List-ID: On Mon, Sep 17, 2018 at 09:54:37AM -0400, Boris Ostrovsky wrote: > On 9/16/18 3:25 PM, Jarkko Sakkinen wrote: > > On Thu, Sep 13, 2018 at 05:25:51PM -0400, Boris Ostrovsky wrote: > >> From: "Dr. Greg Wettstein" > >> > >> Functionality of the xen-tpmfront driver was lost secondary to > >> the introduction of xenbus multi-page support in commit ccc9d90a9a8b > >> ("xenbus_client: Extend interface to support multi-page ring"). > >> > >> In this commit a pointer to the shared page address was being > >> passed to the xenbus_grant_ring() function rather then the > >> address of the shared page itself. This resulted in a situation > > I'm sorry but I'm far from being expert with Xen and this sentence > > confuses me so maybe could open it up a bit. > > > > For me "shared page address" and "address of the shared page" are > > the same thing. What am I missing? I mean just different forms in > > english to describe the exact same thing... > > xenbus_grant_ring() takes as an argument address of the ring shared > between two guests. What Greg was trying to describe was the fact that > existing code instead passes address of location where this address is > stored (i.e. somewhat similar to difference between pointer and pointer > to a pointer). Just to understand this bug better why did not the wrong version cause any undefined behavior? Sounds like a fatal bug. Does this cause crashes? > Would this be better: > > "In this commit pointer to location of the where the shared page address > is stored was being passed to the xenbus_grant_ring() function rather > then the > address of the shared page itself." Yes, definitely! > Or please suggest a better alternative, I'll be happy to amend the > commit message. Thank you. > Thanks. > -boris /Jarkko