linux-kernel - Re: [RFC PATCH v2 1/3] powerpc/prom_init: Replace linux,sml-base/sml-size with linux,sml-log

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Date: Mon, 11 Mar 2024 22:21:38 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Stefan Berger" <stefanb@...ux.ibm.com>, <mpe@...erman.id.au>,
 <linux-integrity@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>
Cc: <linux-kernel@...r.kernel.org>, <rnsastry@...ux.ibm.com>,
 <peterhuewe@....de>, <viparash@...ibm.com>, <devicetree@...r.kernel.org>,
 <jsnitsel@...hat.com>
Subject: Re: [RFC PATCH v2 1/3] powerpc/prom_init: Replace
 linux,sml-base/sml-size with linux,sml-log

On Mon Mar 11, 2024 at 3:20 PM EET, Stefan Berger wrote:
> linux,sml-base holds the address of a buffer with the TPM log. This
> buffer may become invalid after a kexec. To avoid accessing an invalid
> address or corrupted buffer, embed the whole TPM log in the device tree
> property linux,sml-log. This helps to protect the log since it is
> properly carried across a kexec soft reboot with both of the kexec
> syscalls.

- Describe the environment where TPM log gets corrupted.
- Describe why TPM log gets corrupted on kexec.

>
> Avoid having the firmware ingest the whole TPM log when calling
> prom_setprop but only create the linux,sml-log property as a place holder.
> Insert the actual TPM log during the tree flattening phase.

This commit message should shed some light about reasons of the
corruption in order to conclude that it should be fixed up like
this. I.e. why the "post-state" is a legit state where can be
continued despite a log being corrupted. Especially in security
features this is pretty essential information.

BR, Jarkko