tpm, tpm_tis: Avoid cache incoherency in test for interrupts

The interrupt handler that sets the boolean variable irq_tested may run on
another CPU as the thread that checks irq_tested as part of the irq test in
tpm_tis_send().

Since nothing guarantees cache coherency between CPUs for unsynchronized
accesses to boolean variables the testing thread might not perceive the
value change done in the interrupt handler.

Avoid this issue by setting the bit TPM_TIS_IRQ_TESTED in the flags field
of the tpm_tis_data struct and by accessing this field with the bit
manipulating functions that provide cache coherency.

Also convert all other existing sites to use the proper macros when
accessing this bitfield.

Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Tested-by: Michael Niewöhner <linux@mniewoehner.de>
Tested-by: Jarkko Sakkinen <jarkko@kernel.org>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

3 files changed, 13 insertions, 12 deletions

diff --git a/drivers/char/tpm/tpm_tis.c b/drivers/char/tpm/tpm_tis.c
index ed5dabd3c72d..914abc58a328 100644
--- a/drivers/char/tpm/tpm_tis.c
+++ b/drivers/char/tpm/tpm_tis.c
@@ -227,7 +227,7 @@ static int tpm_tis_init(struct device *dev, struct tpm_info *tpm_info)
 		irq = tpm_info->irq;
 
 	if (itpm || is_itpm(ACPI_COMPANION(dev)))
-		phy->priv.flags |= TPM_TIS_ITPM_WORKAROUND;
+		set_bit(TPM_TIS_ITPM_WORKAROUND, &phy->priv.flags);
 
 	return tpm_tis_core_init(dev, &phy->priv, irq, &tpm_tcg,
 				 ACPI_HANDLE(dev));
diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 3f98e587b3e8..57fd315a1d50 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -351,7 +351,7 @@ static int tpm_tis_send_data(struct tpm_chip *chip, const u8 *buf, size_t len)
 	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
 	int rc, status, burstcnt;
 	size_t count = 0;
-	bool itpm = priv->flags & TPM_TIS_ITPM_WORKAROUND;
+	bool itpm = test_bit(TPM_TIS_ITPM_WORKAROUND, &priv->flags);
 
 	status = tpm_tis_status(chip);
 	if ((status & TPM_STS_COMMAND_READY) == 0) {
@@ -484,7 +484,8 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
 	int rc, irq;
 	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
 
-	if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)
+	if (!(chip->flags & TPM_CHIP_FLAG_IRQ) ||
+	     test_bit(TPM_TIS_IRQ_TESTED, &priv->flags))
 		return tpm_tis_send_main(chip, buf, len);
 
 	/* Verify receipt of the expected IRQ */
@@ -494,11 +495,11 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
 	rc = tpm_tis_send_main(chip, buf, len);
 	priv->irq = irq;
 	chip->flags |= TPM_CHIP_FLAG_IRQ;
-	if (!priv->irq_tested)
+	if (!test_bit(TPM_TIS_IRQ_TESTED, &priv->flags))
 		tpm_msleep(1);
-	if (!priv->irq_tested)
+	if (!test_bit(TPM_TIS_IRQ_TESTED, &priv->flags))
 		disable_interrupts(chip);
-	priv->irq_tested = true;
+	set_bit(TPM_TIS_IRQ_TESTED, &priv->flags);
 	return rc;
 }
 
@@ -641,7 +642,7 @@ static int probe_itpm(struct tpm_chip *chip)
 	size_t len = sizeof(cmd_getticks);
 	u16 vendor;
 
-	if (priv->flags & TPM_TIS_ITPM_WORKAROUND)
+	if (test_bit(TPM_TIS_ITPM_WORKAROUND, &priv->flags))
 		return 0;
 
 	rc = tpm_tis_read16(priv, TPM_DID_VID(0), &vendor);
@@ -661,13 +662,13 @@ static int probe_itpm(struct tpm_chip *chip)
 
 	tpm_tis_ready(chip);
 
-	priv->flags |= TPM_TIS_ITPM_WORKAROUND;
+	set_bit(TPM_TIS_ITPM_WORKAROUND, &priv->flags);
 
 	rc = tpm_tis_send_data(chip, cmd_getticks, len);
 	if (rc == 0)
 		dev_info(&chip->dev, "Detected an iTPM.\n");
 	else {
-		priv->flags &= ~TPM_TIS_ITPM_WORKAROUND;
+		clear_bit(TPM_TIS_ITPM_WORKAROUND, &priv->flags);
 		rc = -EFAULT;
 	}
 
@@ -711,7 +712,7 @@ static irqreturn_t tis_int_handler(int dummy, void *dev_id)
 	if (interrupt == 0)
 		return IRQ_NONE;
 
-	priv->irq_tested = true;
+	set_bit(TPM_TIS_IRQ_TESTED, &priv->flags);
 	if (interrupt & TPM_INTF_DATA_AVAIL_INT)
 		wake_up_interruptible(&priv->read_queue);
 	if (interrupt & TPM_INTF_LOCALITY_CHANGE_INT)
@@ -797,7 +798,7 @@ static int tpm_tis_probe_irq_single(struct tpm_chip *chip, u32 intmask,
 	if (rc < 0)
 		return rc;
 
-	priv->irq_tested = false;
+	clear_bit(TPM_TIS_IRQ_TESTED, &priv->flags);
 
 	/* Generate an interrupt by having the core call through to
 	 * tpm_tis_send
diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
index b68479e0de10..57718f43cf64 100644
--- a/drivers/char/tpm/tpm_tis_core.h
+++ b/drivers/char/tpm/tpm_tis_core.h
@@ -87,13 +87,13 @@ enum tpm_tis_flags {
 	TPM_TIS_ITPM_WORKAROUND		= BIT(0),
 	TPM_TIS_INVALID_STATUS		= BIT(1),
 	TPM_TIS_DEFAULT_CANCELLATION	= BIT(2),
+	TPM_TIS_IRQ_TESTED		= BIT(3),
 };
 
 struct tpm_tis_data {
 	u16 manufacturer_id;
 	int locality;
 	int irq;
-	bool irq_tested;
 	unsigned long flags;
 	void __iomem *ilb_base_addr;
 	u16 clkrun_enabled;