Re: [PATCH v6 1/9] tpm, tpm_tis: Avoid cache incoherency in test for interrupts

[Jarkko Sakkinen]

On Tue, Jun 21, 2022 at 03:24:39PM +0200, Lino Sanfilippo wrote:
> From: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
> 
> 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
> tmp_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@xxxxxxxxxx>
> ---
>  drivers/char/tpm/tpm_tis.c      |  2 +-
>  drivers/char/tpm/tpm_tis_core.c | 21 +++++++++++----------
>  drivers/char/tpm/tpm_tis_core.h |  2 +-
>  3 files changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis.c b/drivers/char/tpm/tpm_tis.c
> index bcff6429e0b4..ce43412eb398 100644
> --- a/drivers/char/tpm/tpm_tis.c
> +++ b/drivers/char/tpm/tpm_tis.c
> @@ -226,7 +226,7 @@ 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 dc56b976d816..b5fd4ff46666 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -343,7 +343,7 @@ 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) {
> @@ -470,7 +470,8 @@ 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 */
> @@ -480,11 +481,11 @@ 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;
>  }
>  
> @@ -627,7 +628,7 @@ 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);
> @@ -647,13 +648,13 @@ 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;
>  	}
>  
> @@ -693,7 +694,7 @@ 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)
> @@ -779,7 +780,7 @@ 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 6c203f36b8a1..bf07379dea42 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -86,13 +86,13 @@ enum tis_defaults {
>  enum tpm_tis_flags {
>  	TPM_TIS_ITPM_WORKAROUND		= BIT(0),
>  	TPM_TIS_INVALID_STATUS		= BIT(1),
> +	TPM_TIS_IRQ_TESTED		= BIT(2),
>  };
>  
>  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;
> -- 
> 2.36.1
> 

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko