linux-kernel - Re: [PATCH v6 6/6] tpm/kexec: Duplicate TPM measurement log in of-tree for kexec

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Date:   Wed, 20 Jul 2022 13:48:40 +0000
From:   Nageswara R Sastry <nasastry@...ibm.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
CC:     "nayna@...ux.ibm.com" <nayna@...ux.ibm.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH v6 6/6] tpm/kexec: Duplicate TPM measurement log in
 of-tree for kexec



________________________________________
> From: Stefan Berger <stefanb@...ux.ibm.com>
> Sent: 07 July 2022 10:50 PM
> To: kexec@...ts.infradead.org; devicetree@...r.kernel.org; linux-integrity@...r.kernel.org; linux-kernel@...r.kernel.org; linuxppc-dev@...ts.ozlabs.org
> Cc: nayna@...ux.ibm.com; Nageswara R Sastry; mpe@...erman.id.au; Stefan Berger; Rob Herring; Frank Rowand; Eric Biederman
> Subject: [PATCH v6 6/6] tpm/kexec: Duplicate TPM measurement log in of-tree for kexec

> The memory area of the TPM measurement log is currently not properly
> duplicated for carrying it across kexec when an Open Firmware
> Devicetree is used. Therefore, the contents of the log get corrupted.
> Fix this for the kexec_file_load() syscall by allocating a buffer and
> copying the contents of the existing log into it. The new buffer is
> preserved across the kexec and a pointer to it is available when the new
> kernel is started. To achieve this, store the allocated buffer's address
> in the flattened device tree (fdt) under the name linux,tpm-kexec-buffer
> and search for this entry early in the kernel startup before the TPM
> subsystem starts up. Adjust the pointer in the of-tree stored under
> linux,sml-base to point to this buffer holding the preserved log. The TPM
> driver can then read the base address from this entry when making the log
> available. Invalidate the log by removing 'linux,sml-base' from the
> devicetree if anything goes wrong with updating the buffer.

> Use subsys_initcall() to call the function to restore the buffer even if
> the TPM subsystem or driver are not used. This allows the buffer to be
> carried across the next kexec without involvement of the TPM subsystem
> and ensures a valid buffer pointed to by the of-tree.

> Use the subsys_initcall(), rather than an ealier initcall, since
> page_is_ram() in get_kexec_buffer() only starts working at this stage.

> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Frank Rowand <frowand.list@...il.com>
> Cc: Eric Biederman <ebiederm@...ssion.com>

> ---
> v6:
> - Define prototype for tpm_add_kexec_buffer under same config options
>  as drivers/of/kexec.c is compiled, provide inline function otherwise.
>   (kernel test robot)

Tested-by: Nageswara R Sastry <rnsastry@...ux.ibm.com>