linux-kernel - Re: [PATCH v2, RESEND 0/3] tpm: retrieve digest size of unknown algorithms from TPM

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Message-ID: <8bbff5b1-f4ba-4e38-57fc-05d9ddabea5c@huawei.com>
Date:   Thu, 27 Sep 2018 08:50:14 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>, <jarkko.sakkinen@...ux.intel.com>
CC:     <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        David Safford <david.safford@...com>
Subject: Re: [PATCH v2, RESEND 0/3] tpm: retrieve digest size of unknown
 algorithms from TPM

On 9/26/2018 8:03 PM, Mimi Zohar wrote:
> On Wed, 2018-09-26 at 10:40 -0400, Mimi Zohar wrote:
>> On Mon, 2018-09-17 at 11:38 +0200, Roberto Sassu wrote:
>>> Resending to maintainer with correct mailing lists in CC.
>>>
>>> The TPM driver currently relies on the crypto subsystem to determine the
>>> digest size of supported TPM algorithms. In the future, TPM vendors might
>>> implement new algorithms in their chips, and those algorithms might not
>>> be supported by the crypto subsystem.
>>>
>>> Usually, vendors provide patches for the new hardware, and likely
>>> the crypto subsystem will be updated before the new algorithm is
>>> introduced. However, old kernels might be updated later, after patches
>>> are included in the mainline kernel. This would leave the opportunity
>>> for attackers to misuse PCRs, as PCR banks with an unknown algorithm
>>> are not extended.
>>>
>>> This patch set provides a long term solution for this issue. If a TPM
>>> algorithm is not known by the crypto subsystem, the TPM driver retrieves
>>> the digest size from the TPM with a PCR read. All the PCR banks are
>>> extended, even if the algorithm is not yet supported by the crypto
>>> subsystem.
>>
>> Other than checking the digest size before copying the pcrread buffer,
>> the patches look good.  Please add my Ack on all 3 patches.
>>
>> (New address) Acked-by: Mimi Zohar <zohar@...ux.ibm.com>
> 
> I've reviewed, and am currently running with these patches.
> 
> Even if the IMA changes were in a separate patch, we wouldn't be able
> to break up the patch set anyway.  Jarkko, I'd appreciate your
> carrying the entire patch set.
> 
> Roberto, a similar change needs to be made for tpm_pcr_extend.  Are
> you planning on posting those changes as well?

Yes, I was planning to send the patch after this patch set is accepted.

Roberto