On Wed, Apr 26, 2023 at 08:29:28PM +0300, Jarkko Sakkinen wrote:
> Set TPM_CHIP_FLAG_SUSPENDED in tpm_pm_suspend() and reset in
> tpm_pm_resume(). While the flag is set, tpm_hwrng() gives back zero bytes.
> This prevents hwrng from racing during resume.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 6e592a065d51 ("tpm: Move Linux RNG connection to hwrng")
> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
Reviewed-by: Jerry Snitselaar <jsnitsel@xxxxxxxxxx
> ---
> drivers/char/tpm/tpm-chip.c | 4 ++++
> drivers/char/tpm/tpm-interface.c | 10 ++++++++++
> include/linux/tpm.h | 13 +++++++------
> 3 files changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 6fdfa65a00c3..6f5ee27aeda1 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -572,6 +572,10 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> {
> struct tpm_chip *chip = container_of(rng, struct tpm_chip, hwrng);
>
> + /* Give back zero bytes, as TPM chip has not yet fully resumed: */
> + if (chip->flags & TPM_CHIP_FLAG_SUSPENDED)
> + return 0;
> +
> return tpm_get_random(chip, data, max);
> }
>
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 7e513b771832..0f941cb32eb1 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -412,6 +412,8 @@ int tpm_pm_suspend(struct device *dev)
> }
>
> suspended:
> + chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> +
> if (rc)
> dev_err(dev, "Ignoring error %d while suspending\n", rc);
> return 0;
> @@ -429,6 +431,14 @@ int tpm_pm_resume(struct device *dev)
> if (chip == NULL)
> return -ENODEV;
>
> + chip->flags &= ~TPM_CHIP_FLAG_SUSPENDED;
> +
> + /*
> + * Guarantee that SUSPENDED is written last, so that hwrng does not
> + * activate before the chip has been fully resumed.
> + */
> + wmb();
> +
> return 0;
> }
> EXPORT_SYMBOL_GPL(tpm_pm_resume);
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 4dc97b9f65fb..d7073dc45444 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -274,13 +274,14 @@ enum tpm2_cc_attrs {
> #define TPM_VID_ATML 0x1114
>
> enum tpm_chip_flags {
> - TPM_CHIP_FLAG_TPM2 = BIT(1),
> - TPM_CHIP_FLAG_IRQ = BIT(2),
> - TPM_CHIP_FLAG_VIRTUAL = BIT(3),
> - TPM_CHIP_FLAG_HAVE_TIMEOUTS = BIT(4),
> - TPM_CHIP_FLAG_ALWAYS_POWERED = BIT(5),
> + TPM_CHIP_FLAG_SUSPENDED = BIT(0),
> + TPM_CHIP_FLAG_TPM2 = BIT(1),
> + TPM_CHIP_FLAG_IRQ = BIT(2),
> + TPM_CHIP_FLAG_VIRTUAL = BIT(3),
> + TPM_CHIP_FLAG_HAVE_TIMEOUTS = BIT(4),
> + TPM_CHIP_FLAG_ALWAYS_POWERED = BIT(5),
> TPM_CHIP_FLAG_FIRMWARE_POWER_MANAGED = BIT(6),
> - TPM_CHIP_FLAG_FIRMWARE_UPGRADE = BIT(7),
> + TPM_CHIP_FLAG_FIRMWARE_UPGRADE = BIT(7),
> };
>
> #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)
> --
> 2.39.2
>
