On Tue Feb 13, 2024 at 7:13 PM EET, James Bottomley wrote: > If some entity is snooping the TPM bus, they can see the random > numbers we're extracting from the TPM and do prediction attacks > against their consumers. Foil this attack by using response > encryption to prevent the attacker from seeing the random sequence. > > Signed-off-by: James Bottomley <[email protected]> > Reviewed-by: Jarkko Sakkinen <[email protected]> > > --- > v7: add review > --- > drivers/char/tpm/tpm2-cmd.c | 21 +++++++++++++++++---- > 1 file changed, 17 insertions(+), 4 deletions(-) > > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c > index a53a843294ed..0cdf892ec2a7 100644 > --- a/drivers/char/tpm/tpm2-cmd.c > +++ b/drivers/char/tpm/tpm2-cmd.c > @@ -292,25 +292,35 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, > size_t max) > if (!num_bytes || max > TPM_MAX_RNG_DATA) > return -EINVAL; > > - err = tpm_buf_init(&buf, 0, 0); > + err = tpm2_start_auth_session(chip); > if (err) > return err; > > + err = tpm_buf_init(&buf, 0, 0); > + if (err) { > + tpm2_end_auth_session(chip); > + return err; > + } > + > do { > - tpm_buf_reset(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_GET_RANDOM); > + tpm_buf_reset(&buf, TPM2_ST_SESSIONS, TPM2_CC_GET_RANDOM); > + tpm_buf_append_hmac_session_opt(chip, &buf, TPM2_SA_ENCRYPT > + | TPM2_SA_CONTINUE_SESSION, > + NULL, 0); > tpm_buf_append_u16(&buf, num_bytes); > + tpm_buf_fill_hmac_session(chip, &buf); > err = tpm_transmit_cmd(chip, &buf, > offsetof(struct tpm2_get_random_out, > buffer), > "attempting get random"); > + err = tpm_buf_check_hmac_response(chip, &buf, err); > if (err) { > if (err > 0) > err = -EIO; > goto out; > } > > - out = (struct tpm2_get_random_out *) > - &buf.data[TPM_HEADER_SIZE]; > + out = (struct tpm2_get_random_out *)tpm_buf_parameters(&buf); > recd = min_t(u32, be16_to_cpu(out->size), num_bytes); > if (tpm_buf_length(&buf) < > TPM_HEADER_SIZE + > @@ -327,9 +337,12 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, > size_t max) > } while (retries-- && total < max); > > tpm_buf_destroy(&buf); > + tpm2_end_auth_session(chip); > + > return total ? total : -EIO; > out: > tpm_buf_destroy(&buf); > + tpm2_end_auth_session(chip); > return err; > } >
ditto BR, Jarkko
