Re: [PATCH v14 16/19] tpm, tpm_tis: Allow locality to be set to a different value

Stefano Garzarella
2025-04-22T10:20:43Z

On Mon, Apr 21, 2025 at 09:27:09AM -0700, Ross Philipson wrote:
>DRTM needs to be able to set the locality used by kernel. Provide
>a one-shot function tpm_chip_set_locality() for the purpose.
>
>Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
>Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
>---
> drivers/char/tpm/tpm-chip.c | 34 ++++++++++++++++++++++++++++++++-
> drivers/char/tpm/tpm_tis_core.c | 2 ++
> include/linux/tpm.h | 4 ++++
> 3 files changed, 39 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>index e25daf2396d3..a603f0dadd43 100644
>--- a/drivers/char/tpm/tpm-chip.c
>+++ b/drivers/char/tpm/tpm-chip.c
>@@ -44,7 +44,7 @@ static int tpm_request_locality(struct tpm_chip *chip)
> if (!chip->ops->request_locality)
> return 0;
>
>- rc = chip->ops->request_locality(chip, 0);
>+ rc = chip->ops->request_locality(chip, chip->kernel_locality);
> if (rc < 0)
> return rc;
>
>@@ -380,6 +380,7 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
> }
>
> chip->locality = -1;
>+ chip->kernel_locality = 0;
> return chip;
>
> out:
>@@ -695,3 +696,34 @@ void tpm_chip_unregister(struct tpm_chip *chip)
> tpm_del_char_device(chip);
> }
> EXPORT_SYMBOL_GPL(tpm_chip_unregister);
>+
>+/**
>+ * tpm_chip_set_locality() - Set the TPM locality kernel uses
>+ * @chip: &tpm_chip instance
>+ * @locality: new locality
>+ *
>+ * This a one-shot function. Returns zero or POSIX error on failure.
>+ */
>+int tpm_chip_set_locality(struct tpm_chip *chip, u8 locality)
>+{
>+ int ret;
>+
>+ if (locality < 0 || locality >= TPM_MAX_LOCALITY)

Since `locality` is unsigned, we can skip the `locality < 0` check.

>+ return -EINVAL;
>+
>+ ret = tpm_try_get_ops(chip);
>+ if (ret)
>+ return ret;
>+
>+ if (!(chip->flags & TPM_CHIP_FLAG_SET_LOCALITY_ENABLED)) {
>+ tpm_put_ops(chip);
>+ return -EINVAL;

IIUC this operation is allowed only one time.
So, this case seems more like an operation that's not allowed because
it's already been done, so what about returning "-EPERM".

Thanks,
Stefano

>+ }
>+
>+ chip->kernel_locality = locality;
>+ chip->flags &= ~TPM_CHIP_FLAG_SET_LOCALITY_ENABLED;
>+ tpm_put_ops(chip);
>+
>+ return 0;
>+}
>+EXPORT_SYMBOL_GPL(tpm_chip_set_locality);
>diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
>index 222081e5c7f7..2bc0cf46adbf 100644
>--- a/drivers/char/tpm/tpm_tis_core.c
>+++ b/drivers/char/tpm/tpm_tis_core.c
>@@ -1124,6 +1124,8 @@ int tpm_tis_core_init(struct device *dev, struct
>tpm_tis_data *priv, int irq,
> if (IS_ERR(chip))
> return PTR_ERR(chip);
>
>+ chip->flags |= TPM_CHIP_FLAG_SET_LOCALITY_ENABLED;
>+
> #ifdef CONFIG_ACPI
> chip->acpi_dev_handle = acpi_dev_handle;
> #endif
>diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>index 86fe8f6a2d52..884791acba2e 100644
>--- a/include/linux/tpm.h
>+++ b/include/linux/tpm.h
>@@ -207,6 +207,8 @@ struct tpm_chip {
>
> /* active locality */
> int locality;
>+ /* the locality used by kernel */
>+ u8 kernel_locality;
>
> #ifdef CONFIG_TCG_TPM2_HMAC
> /* details for communication security via sessions */
>@@ -355,6 +357,7 @@ enum tpm_chip_flags {
> TPM_CHIP_FLAG_SUSPENDED = BIT(8),
> TPM_CHIP_FLAG_HWRNG_DISABLED = BIT(9),
> TPM_CHIP_FLAG_DISABLE = BIT(10),
>+ TPM_CHIP_FLAG_SET_LOCALITY_ENABLED = BIT(11),
> };
>
> #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)
>@@ -448,6 +451,7 @@ static inline u32 tpm2_rc_value(u32 rc)
> extern int tpm_is_tpm2(struct tpm_chip *chip);
> extern __must_check int tpm_try_get_ops(struct tpm_chip *chip);
> extern void tpm_put_ops(struct tpm_chip *chip);
>+int tpm_chip_set_locality(struct tpm_chip *chip, u8 locality);
> extern ssize_t tpm_transmit_cmd(struct tpm_chip *chip, struct tpm_buf *buf,
> size_t min_rsp_body_length, const char *desc);
> extern int tpm_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
>--
>2.39.3
>
>