On 9/26/2018 4:09 PM, Mimi Zohar wrote:
On Wed, 2018-09-05 at 17:03 +0200, Roberto Sassu wrote:
On 9/5/2018 3:43 PM, Jeremy Boone wrote:
Some comments on tpm2_pcr_read below.
The tpm2_pcr_read function uses TPM2_ST_NO_SESSIONS. This means
that the response payload is not integrity protected with an HMAC.
If there is a man-in-the-middle sitting on the serial bus that
connects the TPM peripheral to the processor, they can tamper with
the response parameters.
In your changes to tpm2_pcr_read, the memcpy is now become a
variable-length operation, instead of just copying a fixed number of
bytes. If the MITM modifies the response field out->digest_size
before it is received by the driver, they can make it a very large
value, forcing a buffer overflow of the out->digest array.
Adding a session to the PCR Read command seems like overkill in
this case. I wouldn’t recommend that as a solution here. So to fix
this I would suggest simply checking the digest size before the
memcpy.
Hi Jeremy
ok, thanks.
The hash digest size checking should be based on the size stored in
the active_bank_info, either in 3/3 or as a separate patch.
This can be done after the PCR read requested by
tpm2_init_active_bank_info() to initialize the digest sizes.
Roberto
