linux-kernel - Re: [PATCH v5 2/3] tpm: Add tpm_tis_verify_crc to the tpm_tis_phy

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Date:   Tue, 7 Jun 2022 12:56:03 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Alexander Steffen <Alexander.Steffen@...ineon.com>
Cc:     linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        peterhuewe@....de, jgg@...pe.ca, krzysztof.kozlowski+dt@...aro.org,
        Johannes Holland <johannes.holland@...ineon.com>,
        Amir Mizinski <amirmizi6@...il.com>
Subject: Re: [PATCH v5 2/3] tpm: Add tpm_tis_verify_crc to the
 tpm_tis_phy_ops protocol layer

On Fri, Jun 03, 2022 at 04:35:31PM +0200, Alexander Steffen wrote:
> Some TPMs, e.g. those implementing the I2C variant of TIS, can verify
> data transfers to/from the FIFO with a CRC. The CRC is calculated over
> the entirety of the FIFO register. Since the phy_ops layer is not aware
> when the core layer is done reading/writing the FIFO, CRC verification
> must be triggered from the core layer. To this end, add an optional
> phy_ops API call.
> 
> Co-developed-by: Johannes Holland <johannes.holland@...ineon.com>
> Signed-off-by: Johannes Holland <johannes.holland@...ineon.com>
> Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
> Change-Id: I43716c8d45f62c0fcdaabfc3366f8deb89fd1f32

Strip off Change-Id.

> ---
>  drivers/char/tpm/tpm_tis_core.c | 14 ++++++++++++++
>  drivers/char/tpm/tpm_tis_core.h | 10 ++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index dc56b976d816..757623bacfd5 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -289,6 +289,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  	int size = 0;
>  	int status;
>  	u32 expected;
> +	int rc;
>  
>  	if (count < TPM_HEADER_SIZE) {
>  		size = -EIO;
> @@ -328,6 +329,13 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  		goto out;
>  	}
>  
> +	rc = tpm_tis_verify_crc(priv, (size_t)size, buf);
> +	if (rc < 0) {
> +		dev_err(&chip->dev, "CRC mismatch for response.\n");
> +		size = rc;
> +		goto out;
> +	}
> +
>  out:
>  	tpm_tis_ready(chip);
>  	return size;
> @@ -443,6 +451,12 @@ static int tpm_tis_send_main(struct tpm_chip *chip, const u8 *buf, size_t len)
>  	if (rc < 0)
>  		return rc;
>  
> +	rc = tpm_tis_verify_crc(priv, len, buf);
> +	if (rc < 0) {
> +		dev_err(&chip->dev, "CRC mismatch for command.\n");
> +		return rc;
> +	}
> +
>  	/* go and do it */
>  	rc = tpm_tis_write8(priv, TPM_STS(priv->locality), TPM_STS_GO);
>  	if (rc < 0)
> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> index 6c203f36b8a1..66a5a13cd1df 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -121,6 +121,8 @@ struct tpm_tis_phy_ops {
>  			  u8 *result, enum tpm_tis_io_mode mode);
>  	int (*write_bytes)(struct tpm_tis_data *data, u32 addr, u16 len,
>  			   const u8 *value, enum tpm_tis_io_mode mode);
> +	int (*verify_crc)(struct tpm_tis_data *data, size_t len,
> +			  const u8 *value);
>  };
>  
>  static inline int tpm_tis_read_bytes(struct tpm_tis_data *data, u32 addr,
> @@ -188,6 +190,14 @@ static inline int tpm_tis_write32(struct tpm_tis_data *data, u32 addr,
>  	return rc;
>  }
>  
> +static inline int tpm_tis_verify_crc(struct tpm_tis_data *data, size_t len,
> +				     const u8 *value)
> +{
> +	if (!data->phy_ops->verify_crc)
> +		return 0;

I think it would be more readable to have one empty line here.

> +	return data->phy_ops->verify_crc(data, len, value);
> +}
> +
>  static inline bool is_bsw(void)
>  {
>  #ifdef CONFIG_X86
> -- 
> 2.25.1
> 

Other than that LGTM.

BR, Jarkko