On Tue Feb 13, 2024 at 7:13 PM EET, James Bottomley wrote: > tpm2_pcr_extend() is used by trusted keys to extend a PCR to prevent a > key from being re-loaded until the next reboot. To use this > functionality securely, that extend must be protected by a session > hmac. This patch adds HMAC protection so tampering with the > tpm2_pcr_extend() command in flight is detected. > > Signed-off-by: James Bottomley <[email protected]> > Reviewed-by: Jarkko Sakkinen <[email protected]> > > --- > v7: add review > --- > drivers/char/tpm/tpm2-cmd.c | 27 ++++++++++----------------- > 1 file changed, 10 insertions(+), 17 deletions(-) > > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c > index b0e72fb563d9..a53a843294ed 100644 > --- a/drivers/char/tpm/tpm2-cmd.c > +++ b/drivers/char/tpm/tpm2-cmd.c > @@ -216,13 +216,6 @@ int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx, > return rc; > } > > -struct tpm2_null_auth_area { > - __be32 handle; > - __be16 nonce_size; > - u8 attributes; > - __be16 auth_size; > -} __packed; > - > /** > * tpm2_pcr_extend() - extend a PCR value > * > @@ -236,24 +229,22 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, > struct tpm_digest *digests) > { > struct tpm_buf buf; > - struct tpm2_null_auth_area auth_area; > int rc; > int i; > > - rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND); > + rc = tpm2_start_auth_session(chip); > if (rc) > return rc; > > - tpm_buf_append_u32(&buf, pcr_idx); > + rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND); > + if (rc) { > + tpm2_end_auth_session(chip); > + return rc; > + } > > - 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_name(chip, &buf, pcr_idx, NULL); > + tpm_buf_append_hmac_session(chip, &buf, 0, NULL, 0); > > - tpm_buf_append_u32(&buf, sizeof(struct tpm2_null_auth_area)); > - tpm_buf_append(&buf, (const unsigned char *)&auth_area, > - sizeof(auth_area)); > tpm_buf_append_u32(&buf, chip->nr_allocated_banks); > > for (i = 0; i < chip->nr_allocated_banks; i++) { > @@ -262,7 +253,9 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, > chip->allocated_banks[i].digest_size); > } > > + tpm_buf_fill_hmac_session(chip, &buf); > rc = tpm_transmit_cmd(chip, &buf, 0, "attempting extend a PCR value"); > + rc = tpm_buf_check_hmac_response(chip, &buf, rc); > > tpm_buf_destroy(&buf); >
reviewed-by still applies BR, Jarkko
