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

Jarkko Sakkinen
2022-06-26T06:24:04Z

On Tue, Jun 21, 2022 at 03:24:39PM +0200, Lino Sanfilippo wrote:
> From: Lino Sanfilippo <l.sanfilippo@kunbus.com>
>
> 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@kunbus.com>
> ---
> 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@kernel.org>

BR, Jarkko