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linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Sun, 23 Mar 2025 13:25:15 -0400 In-Reply-To: <20250323140911.226137-11-nstange@suse.de> References: <20250323140911.226137-1-nstange@suse.de> <20250323140911.226137-11-nstange@suse.de> Autocrypt: addr=James.Bottomley@HansenPartnership.com; prefer-encrypt=mutual; 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 8mT2Eh9SkH+YVOmaKsajgZgrBxA7fWmGoxXswEVxJIFj3vW7yNc0C5HaUdYa5iGOMs4kg2ht4s7yy7NRQuh7BifWjo6BQ6k4S1H+6axZucxhSV1L6zN9d+lr3Xo/vy1unzA== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2025-03-23 at 15:09 +0100, Nicolai Stange wrote: > PCR reads aren't currently authenticated even with > CONFIG_TCG_TPM2_HMAC=3Dy yet. The reason being TPM2_PCR_Read can only support an audit session, so it has even more overhead than the usual HMAC session for something you don't care about and because no-one relies on plain reads anyway, relying entities use quotes. > It is probably desirable though, as e.g. IMA does some PCR reads to > form the cumulative boot digest subsequently extended into PCR 10 (an > operation which *is* authenticated). Could you elaborate on what security properties this adds? I can't see any form of attack that could be done by altering the boot aggregate: either the relying party cares, in which case it will quote the boot log and arrive at its own value, or it doesn't, in which case the value in the log is superfluous. > + /* > + * Exclusivity is not needed, but set in the > response. > + * Set it here too, so that the HMAC verification > + * won't fail. > + */ > + tpm_buf_append_hmac_session(chip, &buf, > TPM2_SA_AUDIT > + | > TPM2_SA_AUDIT_EXCLUSIVE, > + NULL, 0); Exclusivity here requires no other command be unaudited between the session starting and now. That means that with the lazy flush scheme you have a reasonable chance of this being violated and triggering an error on the command. Additionally, the response will only have the exclusive flag set if the above condition (no other unaudited command since session start) is true, which it might not be. The problem you're having is that tpm2_auth_check_hmac_response() uses the command session flags to calculate the rpHash, which is a useful short cut because for non-audit sessions they're always the same. If you want to use audit sessions, you have to teach it to dig the response session flags out of the header and use them instead. Regards, James