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Date: Sat, 20 Feb 2021 04:52:15 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Matthew Garrett <matthewgarrett@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
linux-pm@...r.kernel.org, keyrings@...r.kernel.org,
zohar@...ux.ibm.com, jejb@...ux.ibm.com, corbet@....net,
rjw@...ysocki.net, Matthew Garrett <mjg59@...gle.com>
Subject: Re: [PATCH 1/9] tpm: Add support for in-kernel resetting of PCRs
On Sat, Feb 20, 2021 at 01:32:47AM +0000, Matthew Garrett wrote:
Perhaps, prepend with a paragraph elaborating the background just a bit:
"When entering to hibernation, PCR 23 will be used to store a known value.
This value defines a policy for the decryption of the key used to encrypt
the hibernate image."
At minimum that. You can of course edit this however you see fit.
> Add an internal command for resetting a PCR.
>
> Signed-off-by: Matthew Garrett <mjg59@...gle.com>
> ---
> drivers/char/tpm/tpm-interface.c | 28 +++++++++++++++++++++++++
> drivers/char/tpm/tpm.h | 2 ++
> drivers/char/tpm/tpm1-cmd.c | 34 ++++++++++++++++++++++++++++++
> drivers/char/tpm/tpm2-cmd.c | 36 ++++++++++++++++++++++++++++++++
> include/linux/tpm.h | 7 +++++++
> 5 files changed, 107 insertions(+)
>
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 1621ce818705..17b8643ee109 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -342,6 +342,34 @@ 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()
> + */
> +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);
> + goto out;
> + }
> +
> + rc = tpm1_pcr_reset(chip, pcr_idx, "attempting to reset a PCR");
> +
> +out:
> + tpm_put_ops(chip);
> + return rc;
> +}
> +EXPORT_SYMBOL_GPL(tpm_pcr_reset);
> +
> /**
> * 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 947d1db0a5cc..746f7696bdc0 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -176,6 +176,7 @@ int tpm1_get_timeouts(struct tpm_chip *chip);
> unsigned long tpm1_calc_ordinal_duration(struct tpm_chip *chip, u32 ordinal);
> int tpm1_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash,
> const char *log_msg);
> +int tpm1_pcr_reset(struct tpm_chip *chip, u32 pcr_idx, const char *log_msg);
> int tpm1_pcr_read(struct tpm_chip *chip, u32 pcr_idx, u8 *res_buf);
> ssize_t tpm1_getcap(struct tpm_chip *chip, u32 subcap_id, cap_t *cap,
> const char *desc, size_t min_cap_length);
> @@ -220,6 +221,7 @@ 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/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
> index ca7158fa6e6c..36990e9d2dc1 100644
> --- a/drivers/char/tpm/tpm1-cmd.c
> +++ b/drivers/char/tpm/tpm1-cmd.c
> @@ -478,6 +478,40 @@ int tpm1_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash,
> return rc;
> }
>
> +struct tpm_pcr_selection {
> + u16 size_of_select;
> + u8 pcr_select[3];
> +} __packed;
> +
> +#define TPM_ORD_PCR_RESET 200
> +int tpm1_pcr_reset(struct tpm_chip *chip, u32 pcr_idx, const char *log_msg)
> +{
> + struct tpm_pcr_selection selection;
> + struct tpm_buf buf;
> + int i, rc;
> + char tmp;
> +
> + rc = tpm_buf_init(&buf, TPM_TAG_RQU_COMMAND, TPM_ORD_PCR_RESET);
> + if (rc)
> + return rc;
> +
> + selection.size_of_select = 3;
> +
> + for (i = 0; i < selection.size_of_select; i++) {
> + tmp = 0;
> + if (pcr_idx / 3 == i) {
> + pcr_idx -= i * 8;
> + tmp |= 1 << pcr_idx;
> + }
> + selection.pcr_select[i] = tmp;
> + }
> + tpm_buf_append(&buf, (u8 *)&selection, sizeof(selection));
> +
> + rc = tpm_transmit_cmd(chip, &buf, sizeof(selection), log_msg);
> + tpm_buf_destroy(&buf);
> + return rc;
> +}
> +
> #define TPM_ORD_GET_CAP 101
> ssize_t tpm1_getcap(struct tpm_chip *chip, u32 subcap_id, cap_t *cap,
> const char *desc, size_t min_cap_length)
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index eff1f12d981a..9609ae8086c6 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
> + *
> + * @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 8f4ff39f51e7..e2075e2242a0 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -211,6 +211,7 @@ 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,
> @@ -399,6 +400,7 @@ static inline u32 tpm2_rc_value(u32 rc)
> extern int tpm_is_tpm2(struct tpm_chip *chip);
> 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);
> @@ -417,6 +419,11 @@ 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)
> {
> --
> 2.30.0.617.g56c4b15f3c-goog
>
>
/Jarkko
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