linux-kernel - [PATCH v6 2/3] tpm: Add tpm_tis_verify_crc to the tpm_tis_phy

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Date:   Wed, 8 Jun 2022 19:31:12 +0200
From:   Alexander Steffen <Alexander.Steffen@...ineon.com>
To:     <jarkko@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-integrity@...r.kernel.org>
CC:     Alexander Steffen <Alexander.Steffen@...ineon.com>,
        <peterhuewe@....de>, <jgg@...pe.ca>,
        <krzysztof.kozlowski+dt@...aro.org>,
        Johannes Holland <johannes.holland@...ineon.com>,
        Amir Mizinski <amirmizi6@...il.com>
Subject: [PATCH v6 2/3] tpm: Add tpm_tis_verify_crc to the tpm_tis_phy_ops protocol layer

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>
Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
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 ++++++++++
 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;
+	return data->phy_ops->verify_crc(data, len, value);
+}
+
 static inline bool is_bsw(void)
 {
 #ifdef CONFIG_X86
-- 
2.25.1