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

[Nageswara R Sastry <nasastry@in.ibm.com>]

________________________________________
> From: Stefan Berger <stefanb@linux.ibm.com>
> Sent: 07 July 2022 10:50 PM
> To: kexec@lists.infradead.org; devicetree@vger.kernel.org; linux-integrity@vger.kernel.org; linux-kernel@vger.kernel.org; linuxppc-dev@lists.ozlabs.org
> Cc: nayna@linux.ibm.com; Nageswara R Sastry; mpe@ellerman.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@linux.ibm.com>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Frank Rowand <frowand.list@gmail.com>
> Cc: Eric Biederman <ebiederm@xmission.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@linux.ibm.com>