Re: [PATCH] tpm: return a TPM_RC_COMMAND_CODE response if a command isn't implemented

Javier Martinez Canillas
2017-12-07T08:58:41Z

Hello Jarkko,

On 12/07/2017 02:32 AM, Jarkko Sakkinen wrote:
> On Mon, Nov 27, 2017 at 12:30:12AM +0100, Javier Martinez Canillas wrote:
>> According to the TPM Library Specification, a TPM device must do a command
>> header validation before processing and return a TPM_RC_COMMAND_CODE code
>> if the command is not implemented.
>>
>> So user-space will expect to handle that response as an error. But if the
>> in-kernel resource manager is used (/dev/tpmrm?), an -EINVAL errno code is
>> returned instead if the command isn't implemented. This confuses userspace
>> since it doesn't expect that error value.
>>
>> This also isn't consistent with the behavior when not using TPM spaces and
>> accessing the TPM directly (/dev/tpm?). In this case, the command is sent
>> to the TPM even when not implemented and the TPM responds with an error.
>>
>> Instead of returning an -EINVAL errno code when the tpm_validate_command()
>> function fails, synthesize a TPM command response so user-space can get a
>> TPM_RC_COMMAND_CODE as expected when a chip doesn't implement the command.
>>
>> The TPM only sets 12 of the 32 bits in the TPM_RC response, so the TSS and
>> TAB specifications define that higher layers in the stack should use some
>> of the unused 20 bits to specify from which level of the stack the error
>> is coming from.
>>
>> Since the TPM_RC_COMMAND_CODE response code is sent by the kernel resource
>> manager, set the error level to the TAB/RM layer so user-space is aware of
>> this.
>>
>> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
>> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
>>
>> ---
>>
>> Changes since RFCv2:
>> - Set the error level to the TAB/RM layer so user-space is aware that the error
>> is not coming from the TPM (suggested by Philip Tricca and Jarkko Sakkinen).
>>
>> Changes since RFCv1:
>> - Don't pass not validated commands to the TPM, instead return a synthesized
>> response with the correct TPM return code (suggested by Jason Gunthorpe).
>>
>> And example of user-space getting confused by the TPM chardev returning -EINVAL
>> when sending a not supported TPM command can be seen in this tpm2-tools issue:
>>
>> https://github.com/intel/tpm2-tools/issues/621
>>
>> Best regards,
>> Javier
>>
>> drivers/char/tpm/tpm-interface.c | 28 ++++++++++++++++++++--------
>> drivers/char/tpm/tpm.h | 8 ++++++++
>> 2 files changed, 28 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>> index ebe0a1d36d8c..9391811c5f83 100644
>> --- a/drivers/char/tpm/tpm-interface.c
>> +++ b/drivers/char/tpm/tpm-interface.c
>> @@ -328,7 +328,7 @@ unsigned long tpm_calc_ordinal_duration(struct tpm_chip *chip,
>> }
>> EXPORT_SYMBOL_GPL(tpm_calc_ordinal_duration);
>>
>> -static bool tpm_validate_command(struct tpm_chip *chip,
>> +static int tpm_validate_command(struct tpm_chip *chip,
>> struct tpm_space *space,
>> const u8 *cmd,
>> size_t len)
>> @@ -340,10 +340,10 @@ static bool tpm_validate_command(struct tpm_chip *chip,
>> unsigned int nr_handles;
>>
>> if (len < TPM_HEADER_SIZE)
>> - return false;
>> + return -EINVAL;
>>
>> if (!space)
>> - return true;
>> + return 0;
>>
>> if (chip->flags & TPM_CHIP_FLAG_TPM2 && chip->nr_commands) {
>> cc = be32_to_cpu(header->ordinal);
>> @@ -352,7 +352,7 @@ static bool tpm_validate_command(struct tpm_chip *chip,
>> if (i < 0) {
>> dev_dbg(&chip->dev, "0x%04X is an invalid command\n",
>> cc);
>> - return false;
>> + return -EOPNOTSUPP;
>> }
>>
>> attrs = chip->cc_attrs_tbl[i];
>> @@ -362,11 +362,11 @@ static bool tpm_validate_command(struct tpm_chip *chip,
>> goto err_len;
>> }
>>
>> - return true;
>> + return 0;
>> err_len:
>> dev_dbg(&chip->dev,
>> "%s: insufficient command length %zu", __func__, len);
>> - return false;
>> + return -EINVAL;
>> }
>>
>> /**
>> @@ -391,8 +391,20 @@ ssize_t tpm_transmit(struct tpm_chip *chip, struct tpm_space *space,
>> unsigned long stop;
>> bool need_locality;
>>
>> - if (!tpm_validate_command(chip, space, buf, bufsiz))
>> - return -EINVAL;
>> + rc = tpm_validate_command(chip, space, buf, bufsiz);
>> + if (rc == -EINVAL)
>> + return rc;
>> + /*
>> + * If the command is not implemented by the TPM, synthesize a
>> + * response with a TPM2_RC_COMMAND_CODE return for user-space.
>> + */
>> + if (rc == -EOPNOTSUPP) {
>> + header->length = cpu_to_be32(sizeof(*header));
>> + header->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
>> + header->return_code = cpu_to_be32(TPM2_RC_COMMAND_CODE |
>> + TPM2_RESMGRTPM_ERROR_LEVEL);
>> + return bufsiz;
>> + }
>>
>> if (bufsiz > TPM_BUFSIZE)
>> bufsiz = TPM_BUFSIZE;
>> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
>> index c1866cc02e30..b3f9108d3d1f 100644
>> --- a/drivers/char/tpm/tpm.h
>> +++ b/drivers/char/tpm/tpm.h
>> @@ -94,12 +94,20 @@ enum tpm2_structures {
>> TPM2_ST_SESSIONS = 0x8002,
>> };
>>
>> +/* Indicates from what level of the software stack the error comes from */
>> +#define TPM2_RC_LEVEL_SHIFT 16
>> +
>> +#define TPM2_RESMGRTPM_ERROR_LEVEL (11 << TPM2_RC_LEVEL_SHIFT)
>> +#define TPM2_RESMGR_ERROR_LEVEL (12 << TPM2_RC_LEVEL_SHIFT)
>> +#define TPM2_DRIVER_ERROR_LEVEL (13 << TPM2_RC_LEVEL_SHIFT)
>> +
>> enum tpm2_return_codes {
>> TPM2_RC_SUCCESS = 0x0000,
>> TPM2_RC_HASH = 0x0083, /* RC_FMT1 */
>> TPM2_RC_HANDLE = 0x008B,
>> TPM2_RC_INITIALIZE = 0x0100, /* RC_VER1 */
>> TPM2_RC_DISABLED = 0x0120,
>> + TPM2_RC_COMMAND_CODE = 0x0143,
>> TPM2_RC_TESTING = 0x090A, /* RC_WARN */
>> TPM2_RC_REFERENCE_H0 = 0x0910,
>> };
>> --
>> 2.14.3
>>
>
> Please use next time --subject-prefix="PATCH v3".
>

I did. But you are answering to my v1 patch. The v3 can be found here with the
following subject "[PATCH v3] tpm: return a TPM_RC_COMMAND_CODE response if
command is not implemented"

https://patchwork.kernel.org/patch/10084305/

Probably you got confused because I posted 2 RFCs before posting a proper PATCH
and then PATCHv3 and v3.

> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
>

Thanks! As mentioned this is v1, but I guess it also applies to v3 since the
only differences are the removal of the unused defines and the naming change
we discussed.

> /Jarkko
>

Best regards,
--
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat