linux-kernel - Re: [RFC PATCH 0/4] Alternative TPM patches for Trenchboot

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Message-Id: <D5BW0P0HH0QL.7Y4HBLJGEDL8@kernel.org>
Date: Sat, 02 Nov 2024 20:00:31 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>
Cc: <x86@...nel.org>, "Daniel P. Smith" <dpsmith@...rtussolutions.com>,
 "Ross Philipson" <ross.philipson@...cle.com>, "Ard Biesheuvel"
 <ardb@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>, "Peter Huewe"
 <peterhuewe@....de>, "Jason Gunthorpe" <jgg@...pe.ca>, "open list:TPM
 DEVICE DRIVER" <linux-integrity@...r.kernel.org>, "open list"
 <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/4] Alternative TPM patches for Trenchboot

On Sat Nov 2, 2024 at 5:22 PM EET, Jarkko Sakkinen wrote:
> It is not really my problem but I'm also wondering how the
> initialization order is managed. What if e.g. IMA happens to
> initialize before slmodule?

The first obvious observation from Trenchboot implementation is that it
is 9/10 times worst idea ever to have splitted root of trust. Here it
is realized by an LKM for slmodule.

So based on that usually a literal and unquestionable truth, when it
comes to securing platforms, the next question is how to make a single
atomic root of trust for Trenchboot.

There is really only one answer I think of for this it to make slmodule
part of the tpm_tis_core and also init order will be sorted out.

I'll describe the steps forward.

Step 1: declare and refactor that module into
drivers/char/tpm/tpm_tis_slmodule.c and add this to the Makefile:

ifdef CONFIG_SECURE_LAUNCH
obj-$(CONFIG_TCG_TIS_CORE) += tpm_tis_slmodule.o
endif

Step 2: add 'int kernel_locality;' to struct tpm_tis_data.
Step 3: implement tpm_tis_set_locality() internal function.
Step 4: drop sysfs-patch completely (solution is not generic).

BR, Jarkko