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[174.3.196.123]) by smtp.gmail.com with ESMTPSA id 10-v6sm17585068pgb.40.2018.06.22.07.19.52 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Jun 2018 07:19:52 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.86_2) (envelope-from ) id 1fWMul-0004iZ-Sl; Fri, 22 Jun 2018 08:19:51 -0600 Date: Fri, 22 Jun 2018 08:19:51 -0600 From: Jason Gunthorpe To: Stefan Berger Cc: Mimi Zohar , linux-integrity@vger.kernel.org, jarkko.sakkinen@linux.intel.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/4] ima: Use tpm_chip_find() and access TPM functions using it Message-ID: <20180622141951.GC19151@ziepe.ca> References: <20180620204236.1572523-1-stefanb@linux.vnet.ibm.com> <20180620204236.1572523-4-stefanb@linux.vnet.ibm.com> <1529614425.23843.20.camel@linux.vnet.ibm.com> <20180622032536.GB19151@ziepe.ca> <495fdcf7-b5b9-0341-796b-66fdf537811b@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <495fdcf7-b5b9-0341-796b-66fdf537811b@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 22, 2018 at 07:40:37AM -0400, Stefan Berger wrote: > On 06/21/2018 11:25 PM, Jason Gunthorpe wrote: > >On Thu, Jun 21, 2018 at 04:59:55PM -0400, Stefan Berger wrote: > >>On 06/21/2018 04:53 PM, Mimi Zohar wrote: > >>>On Wed, 2018-06-20 at 16:42 -0400, Stefan Berger wrote: > >>>>Rather than accessing the TPM functions using a NULL pointer, which > >>>>causes a lookup for a suitable chip every time, get a hold of a tpm_chip > >>>>and access the TPM functions using this chip. We call the tpm_chip > >>>>ima_tpm_chip and protect it, once initialization is done, using a > >>>>rw_semaphore called ima_tpm_chip_lock. > >>>> > >>>>Use ima_shutdown to release the tpm_chip. > >>>> > >>>>Signed-off-by: Stefan Berger > >>>> security/integrity/ima/ima.h | 3 +++ > >>>> security/integrity/ima/ima_crypto.c | 12 ++++++++++-- > >>>> security/integrity/ima/ima_init.c | 19 ++++++++++++------- > >>>> security/integrity/ima/ima_queue.c | 7 +++++-- > >>>> 4 files changed, 30 insertions(+), 11 deletions(-) > >>>> > >>>>diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h > >>>>index 354bb5716ce3..53a88d578ca5 100644 > >>>>+++ b/security/integrity/ima/ima.h > >>>>@@ -24,6 +24,7 @@ > >>>> #include > >>>> #include > >>>> #include > >>>>+#include > >>>> #include > >>>> > >>>> #include "../integrity.h" > >>>>@@ -56,6 +57,8 @@ extern int ima_policy_flag; > >>>> extern int ima_used_chip; > >>>> extern int ima_hash_algo; > >>>> extern int ima_appraise; > >>>>+extern struct rw_semaphore ima_tpm_chip_lock; > >>>>+extern struct tpm_chip *ima_tpm_chip; > >>>ima_add_templatE_entry() synchronizes appending a measurement to the > >>>measurement list and extending the TPM by taking a lock.  Do we really > >>>need to introduce another lock? > >>This lock protects the ima_tpm_chip from going from != NULL to NULL in the > >>ima_shutdown function. Basically, a global pointer accessed by concurrent > >>threads should be protected if its value can change. However, in this case > >>ima_shutdown would be called so late that there shouldn't be concurrency > >>anymore. Though, I found it better to protect it. Maybe someone else has an > >>opinion? > >Why have a shutdown block? There is no harm in holding a kref if the > >machine is shutting down. > > Looking around at other drivers' usage of the reboot notifier, I find other > drivers as well that use spinlocks or mutexes during the shutdown. Besides > that, we do have the shutdown block already when device_shutdown calls > tpm_class_shutdown() and we get the ops_sem. But the shutdown handler in TPM an actual purpose, we are doing something to the persistent state in the TPM itself during shutdown. I can't see why IMA needs a shutdown handler. You shouldn't add one 'just because' Jason