linux-kernel - Re: [PATCH v5 10/11] PM: hibernate: Verify the digest encryption key

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Message-ID: <Y3GB+CXfAWnV/3qH@sol.localdomain>
Date:   Sun, 13 Nov 2022 15:47:04 -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 <mjg59@...gle.com>,
        Len Brown <len.brown@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v5 10/11] PM: hibernate: Verify the digest encryption key

On Fri, Nov 11, 2022 at 03:16:35PM -0800, Evan Green wrote:
> We want to ensure that the key used to encrypt the digest

What is meant by "the key used to encrypt the digest"?

> was created by
> the kernel during hibernation. To do this we request that the TPM
> include information about the value of PCR 23 at the time of key
> creation in the sealed blob. On resume, we can make sure that the PCR
> information in the creation data blob (already certified by the TPM to
> be accurate) corresponds to the expected value. Since only
> the kernel can touch PCR 23, if an attacker generates a key themselves
> the value of PCR 23 will have been different, allowing us to reject the
> key and boot normally instead of resuming.

It seems that PCR 23 is already included in the authorization policy for the
key, so why is this extra part needed?

- Eric