linux-kernel - Re: [PATCH v4 6/6] tpm: ensure that the output of PCR read contains the correct digest size

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Message-ID: <353ac2d0-591f-f950-f3ad-18e6a4f6085c@huawei.com>
Date:   Thu, 8 Nov 2018 15:47:39 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     <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 v4 6/6] tpm: ensure that the output of PCR read contains
 the correct digest size

On 11/8/2018 3:08 PM, Jarkko Sakkinen wrote:
> On Tue, Nov 06, 2018 at 04:01:59PM +0100, Roberto Sassu wrote:
>> This patch protects against data corruption that could happen in the bus,
>> by checking that 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().
>>
>> This check is performed after information about the PCR banks has been
>> retrieved.
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>> ---
>>   drivers/char/tpm/tpm2-cmd.c | 16 +++++++++++++++-
>>   1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
>> index e2d5b84286a7..3b0b5b032901 100644
>> --- a/drivers/char/tpm/tpm2-cmd.c
>> +++ b/drivers/char/tpm/tpm2-cmd.c
>> @@ -187,15 +187,28 @@ struct tpm2_pcr_read_out {
>>   int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx,
>>   		  struct tpm_digest *digest_struct, u16 *digest_size_ptr)
>>   {
>> +	int i;
>>   	int rc;
>>   	struct tpm_buf buf;
>>   	struct tpm2_pcr_read_out *out;
>>   	u8 pcr_select[TPM2_PCR_SELECT_MIN] = {0};
>>   	u16 digest_size;
>> +	u16 expected_digest_size = 0;
>>   
>>   	if (pcr_idx >= TPM2_PLATFORM_PCR)
>>   		return -EINVAL;
>>   
>> +	if (!digest_size_ptr) {
>> +		for (i = 0; i < chip->nr_active_banks &&
>> +		     chip->active_banks[i].alg_id != digest_struct->alg_id; i++)
>> +			;
> 
> Not sure if the semicolon should be in its own line.

scripts/Lindent suggests:

for (i = 0; i < chip->nr_active_banks &&
      chip->active_banks[i].alg_id != digest_struct->alg_id;
      i++) ;

but this is not accepted by scripts/checkpatch.pl (there are no
warnings/errors on the patch I sent).


>> +
>> +		if (i == chip->nr_active_banks)
>> +			return -EINVAL;
>> +
>> +		expected_digest_size = chip->active_banks[i].digest_size;
>> +	}
>> +
>>   	rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_PCR_READ);
>>   	if (rc)
>>   		return rc;
>> @@ -215,7 +228,8 @@ int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx,
>>   
>>   	out = (struct tpm2_pcr_read_out *)&buf.data[TPM_HEADER_SIZE];
>>   	digest_size = be16_to_cpu(out->digest_size);
>> -	if (digest_size > sizeof(digest_struct->digest)) {
>> +	if (digest_size > sizeof(digest_struct->digest) ||
>> +	    (!digest_size_ptr && digest_size != expected_digest_size)) {
>>   		rc = -EINVAL;
>>   		goto out;
>>   	}
>> -- 
>> 2.17.1
>>
> 
> Please add
> 
> Cc: stable@...r.kernel.org.
> 
> /Jarkko
> 

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