tpm_tis: Probing function for Intel iTPM bug

This patch introduces a function for automatic probing for the Intel iTPM
STS_DATA_EXPECT flaw.

The patch splits the current tpm_tis_send function into 2 parts where the 1st
part is now called tpm_tis_send_data() and merely sends the data to the TPM.
This function is then used for probing. The new tpm_tis_send function now
first calls tpm_tis_send_data and if that succeeds has the TPM process the
command and waits until the response is there.

The probing for the Intel iTPM is only invoked if the user has not passed
itpm=1 as parameter for the module *or* if such a TPM was detected via ACPI.
Previously it was necessary to pass itpm=1 when also passing force=1 to the
module when doing a 'modprobe'. This function is more general than the ACPI
test function and the function relying on ACPI could probably be removed.
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>

drivers/char/tpm/tpm_tis.c

@@ -306,11 +306,10 @@ MODULE_PARM_DESC(itpm, "Force iTPM workarounds (found on some Lenovo laptops)");
  * tpm.c can skip polling for the data to be available as the interrupt is
  * waited for here
  */
-static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
+static int tpm_tis_send_data(struct tpm_chip *chip, u8 *buf, size_t len)
 {
 	int rc, status, burstcnt;
 	size_t count = 0;
-	u32 ordinal;
 
 	if (request_locality(chip, 0) < 0)
 		return -EBUSY;
@@ -345,8 +344,7 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
 
 	/* write last byte */
 	iowrite8(buf[count],
-		 chip->vendor.iobase +
-		 TPM_DATA_FIFO(chip->vendor.locality));
+		 chip->vendor.iobase + TPM_DATA_FIFO(chip->vendor.locality));
 	wait_for_stat(chip, TPM_STS_VALID, chip->vendor.timeout_c,
 		      &chip->vendor.int_queue);
 	status = tpm_tis_status(chip);
@@ -355,6 +353,28 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
 		goto out_err;
 	}
 
+	return 0;
+
+out_err:
+	tpm_tis_ready(chip);
+	release_locality(chip, chip->vendor.locality, 0);
+	return rc;
+}
+
+/*
+ * If interrupts are used (signaled by an irq set in the vendor structure)
+ * tpm.c can skip polling for the data to be available as the interrupt is
+ * waited for here
+ */
+static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
+{
+	int rc;
+	u32 ordinal;
+
+	rc = tpm_tis_send_data(chip, buf, len);
+	if (rc < 0)
+		return rc;
+
 	/* go and do it */
 	iowrite8(TPM_STS_GO,
 		 chip->vendor.iobase + TPM_STS(chip->vendor.locality));
@@ -376,6 +396,47 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
 	return rc;
 }
 
+/*
+ * Early probing for iTPM with STS_DATA_EXPECT flaw.
+ * Try sending command without itpm flag set and if that
+ * fails, repeat with itpm flag set.
+ */
+static int probe_itpm(struct tpm_chip *chip)
+{
+	int rc = 0;
+	u8 cmd_getticks[] = {
+		0x00, 0xc1, 0x00, 0x00, 0x00, 0x0a,
+		0x00, 0x00, 0x00, 0xf1
+	};
+	size_t len = sizeof(cmd_getticks);
+	int rem_itpm = itpm;
+
+	itpm = 0;
+
+	rc = tpm_tis_send_data(chip, cmd_getticks, len);
+	if (rc == 0)
+		goto out;
+
+	tpm_tis_ready(chip);
+	release_locality(chip, chip->vendor.locality, 0);
+
+	itpm = 1;
+
+	rc = tpm_tis_send_data(chip, cmd_getticks, len);
+	if (rc == 0) {
+		dev_info(chip->dev, "Detected an iTPM.\n");
+		rc = 1;
+	} else
+		rc = -EFAULT;
+
+out:
+	itpm = rem_itpm;
+	tpm_tis_ready(chip);
+	release_locality(chip, chip->vendor.locality, 0);
+
+	return rc;
+}
+
 static const struct file_operations tis_ops = {
 	.owner = THIS_MODULE,
 	.llseek = no_llseek,
@@ -515,6 +576,14 @@ static int tpm_tis_init(struct device *dev, resource_size_t start,
 		 "1.2 TPM (device-id 0x%X, rev-id %d)\n",
 		 vendor >> 16, ioread8(chip->vendor.iobase + TPM_RID(0)));
 
+	if (!itpm) {
+		itpm = probe_itpm(chip);
+		if (itpm < 0) {
+			rc = -ENODEV;
+			goto out_err;
+		}
+	}
+
 	if (itpm)
 		dev_info(dev, "Intel iTPM workaround enabled\n");