linux-kernel - Re: [PATCH v7 1/5] tpm: dynamically allocate the allocated

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Message-ID: <32ec194b-811e-fe83-3937-bb82ffad55a7@huawei.com>
Date:   Fri, 11 Jan 2019 08:53:00 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     <zohar@...ux.ibm.com>, <david.safford@...com>,
        <monty.wiseman@...com>, <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <silviu.vlasceanu@...wei.com>
Subject: Re: [PATCH v7 1/5] tpm: dynamically allocate the allocated_banks
 array

On 1/10/2019 6:38 PM, Jarkko Sakkinen wrote:
> On Mon, Jan 07, 2019 at 11:06:33AM +0100, Roberto Sassu wrote:
>> On 12/22/2018 1:03 AM, Jarkko Sakkinen wrote:
>>> On Fri, Dec 21, 2018 at 10:40:09AM +0100, Roberto Sassu wrote:
>>>> On 12/20/2018 3:55 PM, Jarkko Sakkinen wrote:
>>>>> On Thu, Dec 13, 2018 at 11:29:41AM +0100, Roberto Sassu wrote:
>>>>>> This patch renames active_banks (member of tpm_chip) to allocated_banks,
>>>>>> stores the number of allocated PCR banks in nr_allocated_banks (new member
>>>>>> of tpm_chip), and replaces the static array with a pointer to a dynamically
>>>>>> allocated array.
>>>>>>
>>>>>> tpm2_get_pcr_allocation() determines if a PCR bank is allocated by checking
>>>>>> the mask in the TPML_PCR_SELECTION structure returned by the TPM for
>>>>>> TPM2_Get_Capability(). If a bank is not allocated, the TPM returns that
>>>>>> bank in TPML_PCR_SELECTION, with all bits in the mask set to zero. In this
>>>>>> case, the bank is not included in chip->allocated_banks, to avoid that TPM
>>>>>> driver users unnecessarily calculate a digest for that bank.
>>>>>>
>>>>>> One PCR bank with algorithm set to SHA1 is always allocated for TPM 1.x.
>>>>>>
>>>>>> As a consequence of the introduction of nr_allocated_banks,
>>>>>> tpm_pcr_extend() does not check anymore if the algorithm stored in tpm_chip
>>>>>> is equal to zero.
>>>>>>
>>>>>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>>>>>> Tested-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
>>>>>> ---
>>>>>>     drivers/char/tpm/tpm-chip.c      |  1 +
>>>>>>     drivers/char/tpm/tpm-interface.c | 18 +++++++++--------
>>>>>>     drivers/char/tpm/tpm.h           |  3 ++-
>>>>>>     drivers/char/tpm/tpm1-cmd.c      | 10 ++++++++++
>>>>>>     drivers/char/tpm/tpm2-cmd.c      | 34 ++++++++++++++++++++++----------
>>>>>>     5 files changed, 47 insertions(+), 19 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>>>>>> index 32db84683c40..ce851c62bb68 100644
>>>>>> --- a/drivers/char/tpm/tpm-chip.c
>>>>>> +++ b/drivers/char/tpm/tpm-chip.c
>>>>>> @@ -160,6 +160,7 @@ static void tpm_dev_release(struct device *dev)
>>>>>>     	kfree(chip->log.bios_event_log);
>>>>>>     	kfree(chip->work_space.context_buf);
>>>>>>     	kfree(chip->work_space.session_buf);
>>>>>> +	kfree(chip->allocated_banks);
>>>>>>     	kfree(chip);
>>>>>>     }
>>>>>> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>>>>>> index d9439f9abe78..7b80919228be 100644
>>>>>> --- a/drivers/char/tpm/tpm-interface.c
>>>>>> +++ b/drivers/char/tpm/tpm-interface.c
>>>>>> @@ -488,8 +488,7 @@ EXPORT_SYMBOL_GPL(tpm_pcr_read);
>>>>>>     int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash)
>>>>>>     {
>>>>>>     	int rc;
>>>>>> -	struct tpm2_digest digest_list[ARRAY_SIZE(chip->active_banks)];
>>>>>> -	u32 count = 0;
>>>>>> +	struct tpm2_digest *digest_list;
>>>>>>     	int i;
>>>>>>     	chip = tpm_find_get_ops(chip);
>>>>>> @@ -497,16 +496,19 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash)
>>>>>>     		return -ENODEV;
>>>>>>     	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
>>>>>> -		memset(digest_list, 0, sizeof(digest_list));
>>>>>> +		digest_list = kcalloc(chip->nr_allocated_banks,
>>>>>> +				      sizeof(*digest_list), GFP_KERNEL);
>>>>>> +		if (!digest_list)
>>>>>> +			return -ENOMEM;
>>>>>
>>>>> You could preallocate digest list and place it to struct tpm_chip
>>>>> instead of doing it everytime tpm_pcr_extend() called.
>>>>
>>>> This part will be removed with patch 5/5.
>>>
>>> Even if it did, it does not make this patch unbroken.
>>
>> Can two calls to tpm_pcr_extend() be executed at the same time?
>>
>> If yes, the digest list should be protected by a mutex.
> 
> Good question: the answer is no. Mutex locking is done inside the
> transmit flow ATM.

But data are copied before the mutex is locked. Can't a second call
overwrite chip->preallocated_digest_list while the first call is still
writing it?

Roberto


> /Jarkko
> 

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