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


> 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.

Roberto


> /Jarkko
>

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