Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757145AbYJVQJR (ORCPT ); Wed, 22 Oct 2008 12:09:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753733AbYJVQJA (ORCPT ); Wed, 22 Oct 2008 12:09:00 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:49414 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754049AbYJVQI7 (ORCPT ); Wed, 22 Oct 2008 12:08:59 -0400 Date: Wed, 22 Oct 2008 09:49:44 -0500 From: "Serge E. Hallyn" To: Rajiv Andrade Cc: Mimi Zohar , linux-kernel@vger.kernel.org, James Morris , David Safford , Serge Hallyn Subject: Re: [PATCH 1/3] integrity: TPM internel kernel interface Message-ID: <20081022144944.GC21612@us.ibm.com> References: <20081014222312.GA18343@hallyn.com> <1224679633.2786.20.camel@dyn536723.br.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1224679633.2786.20.camel@dyn536723.br.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2902 Lines: 67 Quoting Rajiv Andrade (srajiv@linux.vnet.ibm.com): > On Tue, 2008-10-14 at 17:23 -0500, Serge E. Hallyn wrote: > > Quoting Mimi Zohar (zohar@linux.vnet.ibm.com): > > > The internal TPM kernel interface did not protect itself from > > > the removal of the TPM driver, while being used. We continue > > > to protect the tpm_chip_list using the driver_lock as before, > > > and are using an rcu lock to protect readers. The internal TPM > > > > I still would like to see this spelled out somewhere - correct me > > if I'm wrong but none of the patches sent so far have this spelled > > out in in-line comments, do they? > > > > It does look sane: > > > > 1. writes to tpm_chip_list are protected by driver_lock > > 2. readers of the list are protected by rcu > > 3. chips which are read from the tpm_chip_list, if they > > are used outside of the rcu_read_lock(), are pinned > > using get_device(chip->dev) before releasing the > > rcu_read_lock. > > > > Like I say it looks sane, but something like the above summary > > could stand to be in a comment on top of tpm.c or something. > > > No problem, I'll submit a patch containing a proper comment section to > be applied on top of these, maybe after they get accepted. Great, thanks. > > > kernel interface now protects itself from the driver being > > > removed by incrementing the module reference count. > > > > > > Resubmitting integrity-tpm-internal-kernel-interface.patch, which > > > was previously Signed-off-by Kylene Hall. > > > Updated per feedback: > > > > > > Adds the following support: > > > - make internal kernel interface to transmit TPM commands global > > > - adds reading a pcr value > > > - adds extending a pcr value > > > - adds lookup the tpm_chip for given chip number and type > > > > > > Signed-off-by: Mimi Zohar > > > Signed-off-by: Rajiv Andrade > > > > Now there are other, existing callers of tpm_transmit. Are they > > all protected by sysfs pinning the kobject and thereby the device, > > for the duration of the call? > > > > They aren't called through sysfs, but are still protected. These new > functions get chip data consistently by using rcu_read. Then, after > computing what's intended to be written back to the chip, tpm_transmit > sends the new data while using tpm_mutex, so both operations are > performed without the risk of a race condition. Can you show me where the refcount for dev is incremented (under the rcu_read_lock), either in sysfs code or tpm code? I'm not finding it, but it may just be done in some subtle way that I'm glossing over. thanks, -serge -- 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/