linux-kernel - Re: [PATCH v3 5/5] tpm: ensure that output of PCR read contains the correct digest size

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Message-ID: <alpine.DEB.2.21.1811011631010.14303@jsakkine-mobl1>
Date:   Thu, 1 Nov 2018 16:32:48 +0200 (EET)
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        zohar@...ux.ibm.com, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v3 5/5] tpm: ensure that output of PCR read contains the
 correct digest size

On Wed, 31 Oct 2018, Roberto Sassu wrote:
> On 10/30/2018 8:52 PM, Jarkko Sakkinen wrote:
>> On Tue, 30 Oct 2018, Roberto Sassu wrote:
>>> This patch ensures that the digest size returned by the TPM during a PCR
>>> read matches the size of the algorithm passed as argument to
>>> tpm2_pcr_read(). The check is performed after information about the PCR
>>> banks has been retrieved.
>>> 
>>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>> 
>> What is the scenarion when this can happen (should be explained in
>> the commit message)?
>
> Without an HMAC session, the request/response payload can be modified.
> This patch ensures that the digest size in the payload is equal to the
> size of the algorithm specified by the caller.

i.e. it protect against memory corruption that could happen in the bus?
Please state this.

> For me it is ok to remove this patch from the set. It was requested by
> Mimi.

For me it is not ok remove this patch :-) I just want that note to the
commit message in order to have it documented.

/Jarkko