Re: [PATCH v7 6/6] tpm/kexec: Duplicate TPM measurement log in of-tree for kexec

Rob Herring
2022-08-22T17:59:36Z

On Fri, 12 Aug 2022 12:43:05 -0400, Stefan Berger wrote:
> 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>
> Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.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)
>
> v4:
> - Added #include <linux/vmalloc.h> due to parisc
> - Use phys_addr_t for physical address rather than void *
> - Remove linux,sml-base if the buffer cannot be updated after a kexec
> - Added __init to functions where possible
> ---
> drivers/of/kexec.c | 216 +++++++++++++++++++++++++++++++++++++++++-
> include/linux/kexec.h | 6 ++
> include/linux/of.h | 9 +-
> kernel/kexec_file.c | 6 ++
> 4 files changed, 234 insertions(+), 3 deletions(-)
>

Reviewed-by: Rob Herring <robh@kernel.org>