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Subject: Re: [PATCH v2 3/4] ima: Use tpm_chip_find() and access TPM functions
 using it
To:     Mimi Zohar <zohar@linux.vnet.ibm.com>,
        linux-integrity@vger.kernel.org, jarkko.sakkinen@linux.intel.com
Cc:     jgg@ziepe.ca, linux-kernel@vger.kernel.org
References: <20180620204236.1572523-1-stefanb@linux.vnet.ibm.com>
 <20180620204236.1572523-4-stefanb@linux.vnet.ibm.com>
 <1529614425.23843.20.camel@linux.vnet.ibm.com>
From:   Stefan Berger <stefanb@linux.vnet.ibm.com>
Date:   Thu, 21 Jun 2018 16:59:55 -0400
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On 06/21/2018 04:53 PM, Mimi Zohar wrote:
> On Wed, 2018-06-20 at 16:42 -0400, Stefan Berger wrote:
>> Rather than accessing the TPM functions using a NULL pointer, which
>> causes a lookup for a suitable chip every time, get a hold of a tpm_chip
>> and access the TPM functions using this chip. We call the tpm_chip
>> ima_tpm_chip and protect it, once initialization is done, using a
>> rw_semaphore called ima_tpm_chip_lock.
>>
>> Use ima_shutdown to release the tpm_chip.
>>
>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>> ---
>>   security/integrity/ima/ima.h        |  3 +++
>>   security/integrity/ima/ima_crypto.c | 12 ++++++++++--
>>   security/integrity/ima/ima_init.c   | 19 ++++++++++++-------
>>   security/integrity/ima/ima_queue.c  |  7 +++++--
>>   4 files changed, 30 insertions(+), 11 deletions(-)
>>
>> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
>> index 354bb5716ce3..53a88d578ca5 100644
>> --- a/security/integrity/ima/ima.h
>> +++ b/security/integrity/ima/ima.h
>> @@ -24,6 +24,7 @@
>>   #include <linux/hash.h>
>>   #include <linux/tpm.h>
>>   #include <linux/audit.h>
>> +#include <linux/rwsem.h>
>>   #include <crypto/hash_info.h>
>>
>>   #include "../integrity.h"
>> @@ -56,6 +57,8 @@ extern int ima_policy_flag;
>>   extern int ima_used_chip;
>>   extern int ima_hash_algo;
>>   extern int ima_appraise;
>> +extern struct rw_semaphore ima_tpm_chip_lock;
>> +extern struct tpm_chip *ima_tpm_chip;
>
> ima_add_templatE_entry() synchronizes appending a measurement to the
> measurement list and extending the TPM by taking a lock.  Do we really
> need to introduce another lock?

This lock protects the ima_tpm_chip from going from != NULL to NULL in 
the ima_shutdown function. Basically, a global pointer accessed by 
concurrent threads should be protected if its value can change. However, 
in this case ima_shutdown would be called so late that there shouldn't 
be concurrency anymore. Though, I found it better to protect it. Maybe 
someone else has an opinion?

     Stefan
>
> Mimi
>
>>   /* IMA event related data */
>>   struct ima_event_data {
>> diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
>> index 4e085a17124f..da7715240476 100644
>> --- a/security/integrity/ima/ima_crypto.c
>> +++ b/security/integrity/ima/ima_crypto.c
>> @@ -631,10 +631,18 @@ int ima_calc_buffer_hash(const void *buf, loff_t len,
>>
>>   static void __init ima_pcrread(int idx, u8 *pcr)
>>   {
>> +	int result = 0;
>> +
>> +	down_read(&ima_tpm_chip_lock);
>> +
>>   	if (!ima_used_chip)
>> -		return;
>> +		goto out;
>> +
>> +	result = tpm_pcr_read(ima_tpm_chip, idx, pcr);
>> +out:
>> +	up_read(&ima_tpm_chip_lock);
>>
>> -	if (tpm_pcr_read(NULL, idx, pcr) != 0)
>> +	if (result != 0)
>>   		pr_err("Error Communicating to TPM chip\n");
>>   }
>>
>> diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
>> index 8a5258eb32b6..24db06c4f463 100644
>> --- a/security/integrity/ima/ima_init.c
>> +++ b/security/integrity/ima/ima_init.c
>> @@ -28,6 +28,8 @@
>>   /* name for boot aggregate entry */
>>   static const char *boot_aggregate_name = "boot_aggregate";
>>   int ima_used_chip;
>> +struct rw_semaphore ima_tpm_chip_lock = __RWSEM_INITIALIZER(ima_tpm_chip_lock);
>> +struct tpm_chip *ima_tpm_chip;
>>
>>   /* Add the boot aggregate to the IMA measurement list and extend
>>    * the PCR register.
>> @@ -108,6 +110,13 @@ void __init ima_load_x509(void)
>>   static int ima_shutdown(struct notifier_block *this, unsigned long action,
>>   			void *data)
>>   {
>> +	down_write(&ima_tpm_chip_lock);
>> +	if (ima_tpm_chip) {
>> +		tpm_chip_put(ima_tpm_chip);
>> +		ima_tpm_chip = NULL;
>> +		ima_used_chip = 0;
>> +	}
>> +	up_write(&ima_tpm_chip_lock);
>>   	return NOTIFY_DONE;
>>   }
>>
>> @@ -118,19 +127,15 @@ static struct notifier_block ima_reboot_notifier = {
>>
>>   int __init ima_init(void)
>>   {
>> -	u8 pcr_i[TPM_DIGEST_SIZE];
>>   	int rc;
>>
>>   	register_reboot_notifier(&ima_reboot_notifier);
>>
>> -	ima_used_chip = 0;
>> -	rc = tpm_pcr_read(NULL, 0, pcr_i);
>> -	if (rc == 0)
>> -		ima_used_chip = 1;
>> +	ima_tpm_chip = tpm_chip_find();
>>
>> +	ima_used_chip = (ima_tpm_chip != NULL);
>>   	if (!ima_used_chip)
>> -		pr_info("No TPM chip found, activating TPM-bypass! (rc=%d)\n",
>> -			rc);
>> +		pr_info("No TPM chip found, activating TPM-bypass!\n");
>>
>>   	rc = integrity_init_keyring(INTEGRITY_KEYRING_IMA);
>>   	if (rc)
>> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
>> index 418f35e38015..6c9427939a28 100644
>> --- a/security/integrity/ima/ima_queue.c
>> +++ b/security/integrity/ima/ima_queue.c
>> @@ -142,10 +142,13 @@ static int ima_pcr_extend(const u8 *hash, int pcr)
>>   {
>>   	int result = 0;
>>
>> +	down_read(&ima_tpm_chip_lock);
>>   	if (!ima_used_chip)
>> -		return result;
>> +		goto out;
>>
>> -	result = tpm_pcr_extend(NULL, pcr, hash);
>> +	result = tpm_pcr_extend(ima_tpm_chip, pcr, hash);
>> +out:
>> +	up_read(&ima_tpm_chip_lock);
>>   	if (result != 0)
>>   		pr_err("Error Communicating to TPM chip, result: %d\n", result);
>>   	return result;