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

Jarkko Sakkinen
2017-12-07T01:32:23Z

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".

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

/Jarkko