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From: Roberto Sassu <roberto.sassu@huawei.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: <zohar@linux.ibm.com>, <linux-integrity@vger.kernel.org>,
	<linux-security-module@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <silviu.vlasceanu@huawei.com>
Subject: Re: [PATCH v3 5/5] tpm: ensure that output of PCR read contains the correct digest size
Date: Wed, 31 Oct 2018 09:16:53 +0100	[thread overview]
Message-ID: <7adca046-ae80-7453-9fee-a802b46ceb86@huawei.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1810302151580.5058@jsakkine-mobl1>

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@huawei.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.

Patch 3/5 only ensures that there is no buffer overflow when data is
copied to the tpm_digest structure passed by the caller.

Patch 5/5 uses the PCR bank information introduced in patch 4/5 to
ensure that the exact amount of data is copied from the response
payload. However, the patch may not help because an attacker can modify
the algorithm in the request payload so that the TPM returns a shorter
digest.

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

Roberto

-- 
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Bo PENG, Jian LI, Yanli SHI

  reply	other threads:[~2018-10-31  8:17 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-30 15:47 [PATCH v3 0/5] tpm: retrieve digest size of unknown algorithms from TPM Roberto Sassu
2018-10-30 15:47 ` [PATCH v3 1/5] tpm: change the end marker of the active_banks array to zero Roberto Sassu
2018-10-30 19:45   ` Jarkko Sakkinen
2018-10-31 14:43   ` Mimi Zohar
2018-11-01 14:42     ` Mimi Zohar
2018-11-05  8:10       ` Roberto Sassu
2018-11-05 13:02         ` Mimi Zohar
2018-11-05  8:07     ` Roberto Sassu
2018-10-30 15:47 ` [PATCH v3 2/5] tpm: rename and export tpm2_digest and tpm2_algorithms Roberto Sassu
2018-10-30 15:47 ` [PATCH v3 3/5] tpm: modify tpm_pcr_read() definition to pass a TPM hash algorithm Roberto Sassu
2018-10-30 15:47 ` [PATCH v3 4/5] tpm: retrieve digest size of unknown algorithms with PCR read Roberto Sassu
2018-11-01 16:02   ` Mimi Zohar
2018-11-01 16:23     ` Mimi Zohar
2018-11-05  9:47     ` Roberto Sassu
2018-11-05 12:01       ` Jarkko Sakkinen
2018-11-05 13:09         ` Roberto Sassu
2018-11-05 14:48           ` Mimi Zohar
2018-11-05 17:13           ` Jarkko Sakkinen
2018-11-05 17:10         ` Jarkko Sakkinen
2018-10-30 15:47 ` [PATCH v3 5/5] tpm: ensure that output of PCR read contains the correct digest size Roberto Sassu
2018-10-30 19:52   ` Jarkko Sakkinen
2018-10-31  8:16     ` Roberto Sassu [this message]
2018-11-01 14:32       ` Jarkko Sakkinen
2018-11-01 16:52   ` Mimi Zohar

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