Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757077AbYJXUQv (ORCPT ); Fri, 24 Oct 2008 16:16:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751777AbYJXUQn (ORCPT ); Fri, 24 Oct 2008 16:16:43 -0400 Received: from igw2.br.ibm.com ([32.104.18.25]:56099 "EHLO igw2.br.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753817AbYJXUQl (ORCPT ); Fri, 24 Oct 2008 16:16:41 -0400 Subject: Re: [PATCH 1/3] integrity: TPM internel kernel interface From: Rajiv Andrade To: "Serge E. Hallyn" Cc: Mimi Zohar , linux-kernel@vger.kernel.org, James Morris , David Safford , Serge Hallyn In-Reply-To: <20081022144944.GC21612@us.ibm.com> References: <20081014222312.GA18343@hallyn.com> <1224679633.2786.20.camel@dyn536723.br.ibm.com> <20081022144944.GC21612@us.ibm.com> Content-Type: text/plain Date: Fri, 24 Oct 2008 18:16:03 -0200 Message-Id: <1224879363.2778.22.camel@blackbox> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3903 Lines: 100 Serge, On Wed, 2008-10-22 at 09:49 -0500, Serge E. Hallyn wrote: > 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. > The refcount is incremented/decremented in tpm_register_hardware() and tpm_remove_hardware() for tpm module, and tpm_open() and tpm_release() for tpm_tis module, all inside tpm.c. The last two are referenced in tpm_tis.c: tpm_tis.c static const struct file_operations tis_ops = { .owner = THIS_MODULE, .llseek = no_llseek, .open = tpm_open, .read = tpm_read, .write = tpm_write, .release = tpm_release, }; thanks, > 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/ -- Rajiv Andrade Security Development IBM Linux Technology Center -- 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/