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Date: Fri, 30 Sep 2022 23:52:05 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Evan Green <evgreen@...omium.org>
Cc: linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
apronin@...omium.org, dlunev@...gle.com,
Pavel Machek <pavel@....cz>, Ben Boeckel <me@...boeckel.net>,
rjw@...ysocki.net, corbet@....net, linux-pm@...r.kernel.org,
zohar@...ux.ibm.com, Kees Cook <keescook@...omium.org>,
Eric Biggers <ebiggers@...nel.org>, jejb@...ux.ibm.com,
gwendal@...omium.org, Matthew Garrett <mgarrett@...ora.tech>,
Matthew Garrett <matthewgarrett@...gle.com>,
Matthew Garrett <mjg59@...gle.com>, Hao Wu <hao.wu@...rik.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Peter Huewe <peterhuewe@....de>, axelj <axelj@...s.com>
Subject: Re: [PATCH v3 01/11] tpm: Add support for in-kernel resetting of PCRs
On Tue, Sep 27, 2022 at 09:49:12AM -0700, Evan Green wrote:
> From: Matthew Garrett <matthewgarrett@...gle.com>
>
> Add an internal command for resetting a PCR. This will be used by the
> encrypted hibernation code to set PCR23 to a known value. The
> hibernation code will seal the hibernation key with a policy specifying
> PCR23 be set to this known value as a mechanism to ensure that the
> hibernation key is genuine. But to do this repeatedly, resetting the PCR
> is necessary as well.
>
> Link: https://lore.kernel.org/lkml/20210220013255.1083202-2-matthewgarrett@google.com/
> Signed-off-by: Matthew Garrett <mjg59@...gle.com>
> Signed-off-by: Evan Green <evgreen@...omium.org>
> ---
>
> Changes in v3:
> - Unify tpm1/2_pcr_reset prototypes (Jarkko)
> - Wait no, remove the TPM1 stuff altogether (Jarkko)
> - Remove extra From tag and blank in commit msg (Jarkko).
>
> drivers/char/tpm/tpm-interface.c | 25 ++++++++++++++++++++++
> drivers/char/tpm/tpm.h | 1 +
> drivers/char/tpm/tpm2-cmd.c | 36 ++++++++++++++++++++++++++++++++
> include/linux/tpm.h | 7 +++++++
> 4 files changed, 69 insertions(+)
>
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 1621ce8187052c..2ac9079860b1e0 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -342,6 +342,31 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
> }
> EXPORT_SYMBOL_GPL(tpm_pcr_extend);
>
> +/**
> + * tpm_pcr_reset - reset the specified PCR
> + * @chip: a &struct tpm_chip instance, %NULL for the default chip
> + * @pcr_idx: the PCR to be reset
> + *
> + * Return: same as with tpm_transmit_cmd(), or ENOTTY for TPM1 devices.
> + */
> +int tpm_pcr_reset(struct tpm_chip *chip, u32 pcr_idx)
> +{
> + int rc;
> +
> + chip = tpm_find_get_ops(chip);
> + if (!chip)
> + return -ENODEV;
> +
> + if (chip->flags & TPM_CHIP_FLAG_TPM2)
> + rc = tpm2_pcr_reset(chip, pcr_idx);
> + else
> + rc = -ENOTTY;
> +
> + tpm_put_ops(chip);
> + return rc;
> +}
> +EXPORT_SYMBOL_GPL(tpm_pcr_reset);
Please rename this as tpm2_pcr_reset() and open code the contents
of the current tpm2_pcd_reset() into it, as this layering is now
obsolete.
> +
> /**
> * tpm_send - send a TPM command
> * @chip: a &struct tpm_chip instance, %NULL for the default chip
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 24ee4e1cc452a0..34e20b3192f833 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -217,6 +217,7 @@ int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
> struct tpm_digest *digest, u16 *digest_size_ptr);
> int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
> struct tpm_digest *digests);
> +int tpm2_pcr_reset(struct tpm_chip *chip, u32 pcr_idx);
> int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max);
> ssize_t tpm2_get_tpm_pt(struct tpm_chip *chip, u32 property_id,
> u32 *value, const char *desc);
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index 65d03867e114c5..69126a6770386e 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -269,6 +269,42 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
> return rc;
> }
>
> +/**
> + * tpm2_pcr_reset() - reset a PCR
> + *
Remove empty line and "Reset a PCR" with a capital.
There might be random conventions in this but I'm now referring
to just what this says:
https://www.kernel.org/doc/html/v5.19/doc-guide/kernel-doc.html
I.e. better to align with documentation for this and future patches.
> + * @chip: TPM chip to use.
> + * @pcr_idx: index of the PCR.
> + *
> + * Return: Same as with tpm_transmit_cmd.
> + */
> +int tpm2_pcr_reset(struct tpm_chip *chip, u32 pcr_idx)
> +{
> + struct tpm_buf buf;
> + struct tpm2_null_auth_area auth_area;
> + int rc;
> +
> + rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_RESET);
> + if (rc)
> + return rc;
> +
> + tpm_buf_append_u32(&buf, pcr_idx);
> +
> + auth_area.handle = cpu_to_be32(TPM2_RS_PW);
> + auth_area.nonce_size = 0;
> + auth_area.attributes = 0;
> + auth_area.auth_size = 0;
> +
> + tpm_buf_append_u32(&buf, sizeof(struct tpm2_null_auth_area));
> + tpm_buf_append(&buf, (const unsigned char *)&auth_area,
> + sizeof(auth_area));
> +
> + rc = tpm_transmit_cmd(chip, &buf, 0, "attempting to reset a PCR");
> +
> + tpm_buf_destroy(&buf);
> +
> + return rc;
> +}
> +
> struct tpm2_get_random_out {
> __be16 size;
> u8 buffer[TPM_MAX_RNG_DATA];
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index dfeb25a0362dee..8320cbac6f4009 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -219,6 +219,7 @@ enum tpm2_command_codes {
> TPM2_CC_HIERARCHY_CONTROL = 0x0121,
> TPM2_CC_HIERARCHY_CHANGE_AUTH = 0x0129,
> TPM2_CC_CREATE_PRIMARY = 0x0131,
> + TPM2_CC_PCR_RESET = 0x013D,
> TPM2_CC_SEQUENCE_COMPLETE = 0x013E,
> TPM2_CC_SELF_TEST = 0x0143,
> TPM2_CC_STARTUP = 0x0144,
> @@ -423,6 +424,7 @@ 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,
> struct tpm_digest *digest);
> +extern int tpm_pcr_reset(struct tpm_chip *chip, u32 pcr_idx);
> extern int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
> struct tpm_digest *digests);
> extern int tpm_send(struct tpm_chip *chip, void *cmd, size_t buflen);
> @@ -440,6 +442,11 @@ static inline int tpm_pcr_read(struct tpm_chip *chip, int pcr_idx,
> return -ENODEV;
> }
>
> +static inline int tpm_pcr_reset(struct tpm_chip *chip, int pcr_idx)
> +{
> + return -ENODEV;
> +}
> +
> static inline int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
> struct tpm_digest *digests)
> {
> --
> 2.31.0
>
BR, Jarkko
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