Re: [RFC PATCH v2 07/13] tpm: enable bank selection for PCR extend

[Nicolai Stange]

Jarkko Sakkinen <jarkko@xxxxxxxxxx> writes:

> On Sun, Mar 23, 2025 at 03:09:05PM +0100, Nicolai Stange wrote:
>> The existing tpm_pcr_extend() extends all of a PCR's allocated banks with
>> the corresponding digest from the provided digests[] argument.
>
> Why not "just" tpm_pcr_extend(). We don't have a concept of
> "non-existing tpm_pcr_extend()".
>
> "tpm_pcr_extend() extends the allocated PCR banks ..."
>
> or something.

Right.


>> 
>> An upcoming code change to IMA will introduce the need to skip over those
>
> Don't talk about upcoming code changes. Just explain why IMA depends on
> the change.

Ok.


>> banks it does not have a hash algorithm implementation available for.
>> 
>> Introduce tpm_pcr_extend_sel() to support this.
>> 
>> tpm_pcr_extend_sel() also expects a digests[] array, always being the
>> number of allocated PCR banks in size, just as it's the case for the
>> existing tpm_pcr_extend(). In addition to that however, it takes a
>> 'banks_skip_mask', and will skip the extension of any bank having its
>> corresponding bit set there.
>> 
>> Signed-off-by: Nicolai Stange <nstange@xxxxxxx>
>> ---
>>  drivers/char/tpm/tpm-interface.c | 29 +++++++++++++++++++++++++++--
>>  drivers/char/tpm/tpm.h           |  3 ++-
>>  drivers/char/tpm/tpm2-cmd.c      | 29 +++++++++++++++++++++++++++--
>>  include/linux/tpm.h              |  3 +++
>>  4 files changed, 59 insertions(+), 5 deletions(-)
>> 
>> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>> index b1daa0d7b341..88b4496de1df 100644
>> --- a/drivers/char/tpm/tpm-interface.c
>> +++ b/drivers/char/tpm/tpm-interface.c
>> @@ -314,6 +314,26 @@ EXPORT_SYMBOL_GPL(tpm_pcr_read);
>>   */
>>  int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
>>  		   struct tpm_digest *digests)
>> +{
>> +	return tpm_pcr_extend_sel(chip, pcr_idx, digests, 0);
>> +}
>> +EXPORT_SYMBOL_GPL(tpm_pcr_extend);
>
> I'd add just an extra argument to tpm_pcr_extend().

Perfect, will do.

Thanks!

Nicolai

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