linux-kernel - Re: [PATCH] tpm: Disable TCG_TPM2

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Message-ID: <aJ9ySGv0JZ0DiNgf@kernel.org>
Date: Fri, 15 Aug 2025 20:45:44 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Chris Fenner <cfenn@...gle.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@....fi>,
	Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
	linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: Disable TCG_TPM2_HMAC by default

On Fri, Aug 15, 2025 at 10:06:36AM -0700, Chris Fenner wrote:
> On Fri, Aug 15, 2025 at 9:27 AM Jarkko Sakkinen <jarkko.sakkinen@....fi> wrote:
> 
> > I'll with shoot another proposal. Let's delete null primary creation
> > code and add a parameter 'tpm.integrity_handle', which will refers to
> > persistent primary handle:
> 
> I'm not yet sure I understand which handle you mean, or what you're
> proposing to do with it. Could you elaborate?

Primary key persistent handle.

In tpm2_start_auth_session() there's

	/* salt key handle */
	tpm_buf_append_u32(&buf, null_key);

Which would become

	/* salt key handle */
	tpm_buf_append_u32(&buf, integrity_handle);

And in beginning of exported functions from tpm2-sessions.c:

	if (!integrity_handle)
		return 0;

And delete from same file:

	1. tpm2_create_*()
	2. tpm2_load_null()

That way the feature makes sense and does not disturb the user who don't
want it as PCRs and random numbers will be integrity proteced agains an
unambiguous key that can be certified.

> 
> Thanks
> Chris

BR, Jarkko