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Date: Mon, 23 May 2022 23:08:34 +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 v3 2/2] tpm: Add tpm_tis_verify_crc to the
tpm_tis_phy_ops protocol layer
On Fri, May 20, 2022 at 07:24:22PM +0200, Alexander Steffen wrote:
> From: Johannes Holland <johannes.holland@...ineon.com>
>
> Other than SPI TPMs, I2C TPMs implement a CRC feature for command and
> response blobs. Add CRC validation to the TIS protocol according to the
> TCG PC Client Platform TPM Profile (PTP) specification for TPM 2.0 v1.04
> revision 14
>
> 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.
>
> Signed-off-by: Johannes Holland <johannes.holland@...ineon.com>
> Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
> ---
> drivers/char/tpm/tpm_tis_core.c | 14 ++++++++++++++
> drivers/char/tpm/tpm_tis_core.h | 10 ++++++++++
> drivers/char/tpm/tpm_tis_i2c.c | 28 ++++++++++++++++++++++++++++
> 3 files changed, 52 insertions(+)
>
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index dc56b976d816..f1c893a5a38f 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, "Error 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, "Error 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;
> + return data->phy_ops->verify_crc(data, len, value);
> +}
> +
> static inline bool is_bsw(void)
> {
> #ifdef CONFIG_X86
> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
> index 5375ebf57007..bfc26c2a4ed6 100644
> --- a/drivers/char/tpm/tpm_tis_i2c.c
> +++ b/drivers/char/tpm/tpm_tis_i2c.c
> @@ -24,6 +24,7 @@
> #include <linux/gpio.h>
> #include <linux/of_irq.h>
> #include <linux/of_gpio.h>
> +#include <linux/crc-ccitt.h>
> #include <linux/tpm.h>
> #include "tpm_tis_core.h"
>
> @@ -33,6 +34,7 @@
> #define TPM_I2C_INTERFACE_CAPABILITY 0x30
> #define TPM_I2C_DEVICE_ADDRESS 0x38
> #define TPM_I2C_DATA_CSUM_ENABLE 0x40
> +#define TPM_DATA_CSUM 0x44
> #define TPM_I2C_DID_VID 0x48
> #define TPM_I2C_RID 0x4C
>
> @@ -269,6 +271,24 @@ static int tpm_tis_i2c_write_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
> return 0;
> }
>
> +static int tpm_tis_i2c_verify_crc(struct tpm_tis_data *data, size_t len,
> + const u8 *value)
> +{
> + u16 crc_tpm, crc_host;
> + int rc;
> +
> + rc = tpm_tis_read16(data, TPM_DATA_CSUM, &crc_tpm);
> + if (rc < 0)
> + return rc;
> +
> + /* reflect crc result, regardless of host endianness */
> + crc_host = swab16(crc_ccitt(0, value, len));
> + if (crc_tpm != crc_host)
> + return -EIO;
> +
> + return 0;
> +}
> +
> static int init_guard_time(struct tpm_tis_i2c_phy *phy)
> {
> u32 i2c_caps;
> @@ -302,12 +322,14 @@ static SIMPLE_DEV_PM_OPS(tpm_tis_pm, tpm_pm_suspend, tpm_tis_resume);
> static const struct tpm_tis_phy_ops tpm_i2c_phy_ops = {
> .read_bytes = tpm_tis_i2c_read_bytes,
> .write_bytes = tpm_tis_i2c_write_bytes,
> + .verify_crc = tpm_tis_i2c_verify_crc,
> };
>
> static int tpm_tis_i2c_probe(struct i2c_client *dev,
> const struct i2c_device_id *id)
> {
> struct tpm_tis_i2c_phy *phy;
> + const u8 crc_enable = 1;
> const u8 locality = 0;
> int ret;
>
> @@ -332,6 +354,12 @@ static int tpm_tis_i2c_probe(struct i2c_client *dev,
> if (ret)
> return ret;
>
> + ret = tpm_tis_i2c_write_bytes(&phy->priv, TPM_I2C_DATA_CSUM_ENABLE,
> + sizeof(crc_enable), &crc_enable,
> + TPM_TIS_PHYS_8);
> + if (ret)
> + return ret;
> +
> return tpm_tis_core_init(&dev->dev, &phy->priv, -1, &tpm_i2c_phy_ops,
> NULL);
> }
> --
> 2.25.1
>
Should be split to two patches: the hook and the implementation for I2C, as
per https://www.kernel.org/doc/html/latest/process/submitting-patches.html#separate-your-changes
BR, Jarkko
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