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

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Message-ID: <4w5oshnh6opkrhngzy74cagd7vio45wz6cv3ltmowfbcipdjvs@rijgzlucl6jd>
Date: Tue, 22 Apr 2025 12:20:29 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Ross Philipson <ross.philipson@...cle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org, 
	kexec@...ts.infradead.org, linux-efi@...r.kernel.org, iommu@...ts.linux.dev, 
	dpsmith@...rtussolutions.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	hpa@...or.com, dave.hansen@...ux.intel.com, ardb@...nel.org, 
	mjg59@...f.ucam.org, James.Bottomley@...senpartnership.com, peterhuewe@....de, 
	jarkko@...nel.org, jgg@...pe.ca, luto@...capital.net, nivedita@...m.mit.edu, 
	herbert@...dor.apana.org.au, davem@...emloft.net, corbet@....net, ebiederm@...ssion.com, 
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, kanth.ghatraju@...cle.com, 
	andrew.cooper3@...rix.com, trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v14 16/19] tpm, tpm_tis: Allow locality to be set to a
 different value

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@...cle.com>
>Signed-off-by: Jarkko Sakkinen <jarkko@...nel.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
>
>