linux-kernel - Re: [PATCH v5 05/11] security: keys: trusted: Allow storage of PCR values in creation data

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Message-ID: <Y3FpI4GHO9pHYZUH@sol.localdomain>
Date:   Sun, 13 Nov 2022 14:01:07 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Evan Green <evgreen@...omium.org>
Cc:     linux-kernel@...r.kernel.org, corbet@....net,
        linux-integrity@...r.kernel.org, gwendal@...omium.org,
        dianders@...omium.org, apronin@...omium.org,
        Pavel Machek <pavel@....cz>, Ben Boeckel <me@...boeckel.net>,
        rjw@...ysocki.net, jejb@...ux.ibm.com,
        Kees Cook <keescook@...omium.org>, dlunev@...gle.com,
        zohar@...ux.ibm.com, Matthew Garrett <mgarrett@...ora.tech>,
        jarkko@...nel.org, linux-pm@...r.kernel.org,
        Matthew Garrett <matthewgarrett@...gle.com>,
        Ben Boeckel <linux@...benboeckel.net>,
        David Howells <dhowells@...hat.com>,
        James Morris <jmorris@...ei.org>,
        Paul Moore <paul@...l-moore.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH v5 05/11] security: keys: trusted: Allow storage of PCR
 values in creation data

On Fri, Nov 11, 2022 at 03:16:30PM -0800, Evan Green wrote:
> +       creationpcrs= hex integer representing the set of PCRs to be
> +                     included in the creation data. For each bit set, the
> +                     corresponding PCR will be included in the key creation
> +                     data. Bit 0 corresponds to PCR0. Currently only the first
> +                     PC standard 24 PCRs are supported on the currently active
> +                     bank. Leading zeroes are optional. TPM2 only.

What does "currently active bank" mean?

> +		/* PCR bitmask */
> +		for (i = 0; i < 3; i++) {
> +			char tmp = 0;
> +
> +			for (j = 0; j < 8; j++) {
> +				char bit = (i * 8) + j;
> +
> +				if (options->creation_pcrs & (1 << bit))
> +					tmp |= (1 << j);
> +			}
> +			tpm_buf_append_u8(&buf, tmp);
> +		}

Why not just:

	tpm_buf_append_u8(&buf, options->creation_pcrs);
	tpm_buf_append_u8(&buf, options->creation_pcrs >> 8);
	tpm_buf_append_u8(&buf, options->creation_pcrs >> 16);

Also what if bit 24 or above is set?  Should an error be returned?

- Eric