Re: [PATCH v7 5/5] tpm: pass an array of tpm_extend_digest structures to tpm_pcr_extend()

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, Jan 21, 2019 at 09:11:21AM +0100, Roberto Sassu wrote:
> On 1/18/2019 4:12 PM, Jarkko Sakkinen wrote:
> > On Thu, Jan 17, 2019 at 08:59:00AM +0100, Roberto Sassu wrote:
> > > On 12/20/2018 4:21 PM, Jarkko Sakkinen wrote:
> > > > On Thu, Dec 13, 2018 at 11:29:45AM +0100, Roberto Sassu wrote:
> > > > > Currently, tpm_pcr_extend() accepts as an input only a SHA1 digest.
> > > > > 
> > > > > This patch modifies the definition of tpm_pcr_extend() to allow other
> > > > > kernel subsystems to pass a digest for each algorithm supported by the TPM.
> > > > > All digests are processed by the TPM in one operation.
> > > > > 
> > > > > If a tpm_pcr_extend() caller provides a subset of the supported algorithms,
> > > > > the TPM driver extends the remaining PCR banks with the first digest
> > > > > passed as an argument to the function.
> > > > > 
> > > > > The new tpm_extend digest structure has been preferred to the tpm_digest
> > > > > structure, to let the caller specify the size of the digest (which may be
> > > > > unknown to the TPM driver).
> > > > > 
> > > > > Due to the API change, ima_pcr_extend() and pcrlock() have been modified.
> > > > > 
> > > > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > > > > ---
> > > > >    drivers/char/tpm/tpm-interface.c   | 24 +++++---------------
> > > > >    drivers/char/tpm/tpm.h             |  5 +++--
> > > > >    drivers/char/tpm/tpm1-cmd.c        | 13 ++++++++---
> > > > >    drivers/char/tpm/tpm2-cmd.c        | 35 +++++++++++++++++++++---------
> > > > >    include/linux/tpm.h                | 13 ++++++++---
> > > > >    security/integrity/ima/ima_queue.c |  5 ++++-
> > > > >    security/keys/trusted.c            |  5 ++++-
> > > > >    7 files changed, 62 insertions(+), 38 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> > > > > index eb7c79ca8a94..911fea19e408 100644
> > > > > --- a/drivers/char/tpm/tpm-interface.c
> > > > > +++ b/drivers/char/tpm/tpm-interface.c
> > > > > @@ -478,42 +478,30 @@ EXPORT_SYMBOL_GPL(tpm_pcr_read);
> > > > >     * tpm_pcr_extend - extend a PCR value in SHA1 bank.
> > > > >     * @chip:	a &struct tpm_chip instance, %NULL for the default chip
> > > > >     * @pcr_idx:	the PCR to be retrieved
> > > > > - * @hash:	the hash value used to extend the PCR value
> > > > > + * @count:	number of tpm_extend_digest structures
> > > > > + * @digests:	array of tpm_extend_digest structures used to extend PCRs
> > > > >     *
> > > > >     * Note: with TPM 2.0 extends also those banks for which no digest was
> > > > >     * specified in order to prevent malicious use of those PCR banks.
> > > > >     *
> > > > >     * Return: same as with tpm_transmit_cmd()
> > > > >     */
> > > > > -int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash)
> > > > > +int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, u32 count,
> > > > > +		   const struct tpm_extend_digest *digests)
> > > > 
> > > > Remove const. Document how @digests is used  like the special meaning
> > > > of the first index. I faintly remember asking this last time.
> > > > 
> > > > >    {
> > > > >    	int rc;
> > > > > -	struct tpm_digest *digest_list;
> > > > > -	int i;
> > > > >    	chip = tpm_find_get_ops(chip);
> > > > >    	if (!chip)
> > > > >    		return -ENODEV;
> > > > >    	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
> > > > > -		digest_list = kcalloc(chip->nr_allocated_banks,
> > > > > -				      sizeof(*digest_list), GFP_KERNEL);
> > > > > -		if (!digest_list)
> > > > > -			return -ENOMEM;
> > > > > -
> > > > > -		for (i = 0; i < chip->nr_allocated_banks; i++) {
> > > > > -			digest_list[i].alg_id = chip->allocated_banks[i].alg_id;
> > > > > -			memcpy(digest_list[i].digest, hash, TPM_DIGEST_SIZE);
> > > > > -		}
> > > > > -
> > > > > -		rc = tpm2_pcr_extend(chip, pcr_idx, chip->nr_allocated_banks,
> > > > > -				     digest_list);
> > > > > -		kfree(digest_list);
> > > > > +		rc = tpm2_pcr_extend(chip, pcr_idx, count, digests);
> > > > >    		tpm_put_ops(chip);
> > > > >    		return rc;
> > > > >    	}
> > > > > -	rc = tpm1_pcr_extend(chip, pcr_idx, hash,
> > > > > +	rc = tpm1_pcr_extend(chip, pcr_idx, count, digests,
> > > > >    			     "attempting extend a PCR value");
> > > > 
> > > > The validation is missing that the provided array has only one element
> > > > and the algorithm is SHA1. Could be done also inside tpm1_pcr_extend()
> > > > but what you are doing to that function does not make any sense so
> > > > better to do it here.
> > > > 
> > > > >    	tpm_put_ops(chip);
> > > > >    	return rc;
> > > > > diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> > > > > index 64d93d26087f..6b446504d2fe 100644
> > > > > --- a/drivers/char/tpm/tpm.h
> > > > > +++ b/drivers/char/tpm/tpm.h
> > > > > @@ -504,7 +504,8 @@ int tpm1_auto_startup(struct tpm_chip *chip);
> > > > >    int tpm1_do_selftest(struct tpm_chip *chip);
> > > > >    int tpm1_get_timeouts(struct tpm_chip *chip);
> > > > >    unsigned long tpm1_calc_ordinal_duration(struct tpm_chip *chip, u32 ordinal);
> > > > > -int tpm1_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash,
> > > > > +int tpm1_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, u32 count,
> > > > > +		    const struct tpm_extend_digest *digests,
> > > > >    		    const char *log_msg);
> > > > >    int tpm1_pcr_read(struct tpm_chip *chip, u32 pcr_idx, u8 *res_buf);
> > > > >    ssize_t tpm1_getcap(struct tpm_chip *chip, u32 subcap_id, cap_t *cap,
> > > > > @@ -551,7 +552,7 @@ int tpm2_get_timeouts(struct tpm_chip *chip);
> > > > >    int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
> > > > >    		  struct tpm_digest *digest, u16 *digest_size_ptr);
> > > > >    int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, u32 count,
> > > > > -		    struct tpm_digest *digests);
> > > > > +		    const struct tpm_extend_digest *digests);
> > > > >    int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max);
> > > > >    void tpm2_flush_context_cmd(struct tpm_chip *chip, u32 handle,
> > > > >    			    unsigned int flags);
> > > > > diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
> > > > > index 8b70a7f884a7..04ee10284b8c 100644
> > > > > --- a/drivers/char/tpm/tpm1-cmd.c
> > > > > +++ b/drivers/char/tpm/tpm1-cmd.c
> > > > > @@ -449,12 +449,20 @@ int tpm1_get_timeouts(struct tpm_chip *chip)
> > > > >    }
> > > > >    #define TPM_ORD_PCR_EXTEND 20
> > > > > -int tpm1_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash,
> > > > > +int tpm1_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, u32 count,
> > > > > +		    const struct tpm_extend_digest *digests,
> > > > >    		    const char *log_msg)
> > > > >    {
> > > > >    	struct tpm_buf buf;
> > > > > +	u8 dummy_hash[TPM_DIGEST_SIZE] = { 0 };
> > > > > +	const u8 *hash;
> > > > >    	int rc;
> > > > > +	hash = dummy_hash;
> > > > > +	if (count)
> > > > > +		memcpy(dummy_hash, digests[0].data,
> > > > > +		       min(digests[0].size, (u16)sizeof(dummy_hash)));
> > > > > +
> > > > 
> > > > You copy memory from one place to another without any good reason to do
> > > > so. My suggestion is just not to change tpm1_pcr_extend() at all.
> > > > 
> > > > >    	rc = tpm_buf_init(&buf, TPM_TAG_RQU_COMMAND, TPM_ORD_PCR_EXTEND);
> > > > >    	if (rc)
> > > > >    		return rc;
> > > > > @@ -743,7 +751,6 @@ int tpm1_auto_startup(struct tpm_chip *chip)
> > > > >     */
> > > > >    int tpm1_pm_suspend(struct tpm_chip *chip, u32 tpm_suspend_pcr)
> > > > >    {
> > > > > -	u8 dummy_hash[TPM_DIGEST_SIZE] = { 0 };
> > > > >    	struct tpm_buf buf;
> > > > >    	unsigned int try;
> > > > >    	int rc;
> > > > > @@ -751,7 +758,7 @@ int tpm1_pm_suspend(struct tpm_chip *chip, u32 tpm_suspend_pcr)
> > > > >    	/* for buggy tpm, flush pcrs with extend to selected dummy */
> > > > >    	if (tpm_suspend_pcr)
> > > > > -		rc = tpm1_pcr_extend(chip, tpm_suspend_pcr, dummy_hash,
> > > > > +		rc = tpm1_pcr_extend(chip, tpm_suspend_pcr, 0, NULL,
> > > > >    				     "extending dummy pcr before suspend");
> > > > >    	rc = tpm_buf_init(&buf, TPM_TAG_RQU_COMMAND, TPM_ORD_SAVESTATE);
> > > > > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > > > > index 6ce5173cf0e5..77b5808270c6 100644
> > > > > --- a/drivers/char/tpm/tpm2-cmd.c
> > > > > +++ b/drivers/char/tpm/tpm2-cmd.c
> > > > > @@ -247,21 +247,22 @@ struct tpm2_null_auth_area {
> > > > >     *
> > > > >     * @chip:	TPM chip to use.
> > > > >     * @pcr_idx:	index of the PCR.
> > > > > - * @count:	number of digests passed.
> > > > > - * @digests:	list of pcr banks and corresponding digest values to extend.
> > > > > + * @count:	number of tpm_extend_digest passed.
> > > > > + * @digests:	array of tpm_extend_digest with digest values to extend.
> > > > >     *
> > > > >     * Return: Same as with tpm_transmit_cmd.
> > > > >     */
> > > > 
> > > > The documentation about @digests.
> > > > 
> > > > >    int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, u32 count,
> > > > > -		    struct tpm_digest *digests)
> > > > > +		    const struct tpm_extend_digest *digests)
> > > > >    {
> > > > >    	struct tpm_buf buf;
> > > > >    	struct tpm2_null_auth_area auth_area;
> > > > > +	const struct tpm_extend_digest *digest;
> > > > > +	u8 dummy_hash[SHA512_DIGEST_SIZE] = { 0 };
> > > > > +	const u8 *hash;
> > > > >    	int rc;
> > > > >    	int i;
> > > > > -
> > > > > -	if (count > chip->nr_allocated_banks)
> > > > > -		return -EINVAL;
> > > > > +	int j;
> > > > >    	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND);
> > > > >    	if (rc)
> > > > > @@ -277,11 +278,25 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, u32 count,
> > > > >    	tpm_buf_append_u32(&buf, sizeof(struct tpm2_null_auth_area));
> > > > >    	tpm_buf_append(&buf, (const unsigned char *)&auth_area,
> > > > >    		       sizeof(auth_area));
> > > > > -	tpm_buf_append_u32(&buf, count);
> > > > > +	tpm_buf_append_u32(&buf, chip->nr_allocated_banks);
> > > > > +
> > > > > +	if (count)
> > > > > +		memcpy(dummy_hash, digests[0].data, digests[0].size);
> > > > > +
> > > > > +	for (i = 0; i < chip->nr_allocated_banks; i++) {
> > > > > +		tpm_buf_append_u16(&buf, chip->allocated_banks[i].alg_id);
> > > > > +
> > > > > +		hash = dummy_hash;
> > > > > +		for (j = 0; j < count; j++) {
> > > > > +			digest = digests + j;
> > > > > +
> > > > > +			if (digest->alg_id == chip->allocated_banks[i].alg_id) {
> > > > > +				hash = digest->data;
> > > > > +				break;
> > > > 
> > > > I think the whole design is just wrong. I did re-read your response to
> > > > v6 again and I'm very sorry, but I just don't get this. Caller has all
> > > > the information (from struct tpm_chip) to give the correct data. This
> > > > function should validate that data (check algorithm ID and that's it).
> > > 
> > > The question is if checking tpm->allocated_banks is a strict
> > > requirement, or we can allow callers to use the algorithm they are
> > > currently using, without further modifications.
> > 
> > If you want to know what is available, you can use that array.
> > 
> > > > Extending with the dummy hash should be done by the caller when
> > > > preparing the array, not baked into this function. This kind of also
> > > > makes obvious that we don't need this new struct. There should never be
> > > > a local variable (whose size is BTW randomly chosen) called dummy_hash.
> > > 
> > > This means duplicating the code for each caller. Currently, this work is
> > > done by the TPM driver.
> > 
> > It is better than fix the usage pattern like this. Not only that, but
> > this somewhat complicated behavior now completely undocumented in the
> > function description.
> > 
> > You are making strong assumptions how some other subsystem might use
> > extend operation. I will rather accept redundancy and consider
> > consolidation later when there are two clients. Rather keep the TPM
> > provided function simple and stupid.
> 
> Ok, if I understood it correctly, every caller of tpm_pcr_extend() will pass
> an array of tpm_digest structures.
> 
> I will not introduce a new structure, as the caller has to use
> algorithms from chip->allocated_banks and passing the digest size is not
> necessary.
> 
> tpm_pcr_extend() will reject incomplete arrays (one or more algorithms
> are missing). To simplify even more tpm_pcr_extend(), I assume and check
> that passed algorithms are in the same order as those in
> chip->allocated_banks.
> 
> I will remove the 'count' parameter from tpm_pcr_extend(), as the number
> of tpm_digest structures will be always chip->nr_allocated_banks.

Sounds like a plan. I think some redundancy is almost always better than
hard to undestand API.

/Jarkko