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SubjectRe: [PATCH v4 1/6] tpm: dynamically allocate active_banks array
On Thu, Nov 08, 2018 at 07:20:51PM +0530, Nayna Jain wrote:
> Based on a discussion with Ken, the count in the TPML_PCR_SELECTION returns
> the number of possible algorithms supported. In the example below, two
> possible algorithms - SHA1 and SHA256 - are returned.
>
> # /usr/local/bin/tssgetcapability -cap 5
> 2 PCR selections
>     hash TPM_ALG_SHA1
>     TPMS_PCR_SELECTION length 3
>     ff ff ff
>     hash TPM_ALG_SHA256
>     TPMS_PCR_SELECTION length 3
>     00 00 00
>
> The pcr_select fields - "ff ff ff" and "00 00 00" - are bit masks for the
> enabled PCRs. The SHA1 bank is enabled for all PCRs (0-23), while the SHA256
> bank is not enabled.
>
> The current code works, but it unnecessarily extends some banks. Instead of
> basing the number of active banks on the number of algorithms returned, it
> should be based on the pcr_select field.
>
>    - Mimi & Nayna

I would just allocate array of the size of possible banks and grow
nr_active_banks for active algorithms to keep the code simple because
we are talking about insignificant amount of wasted space (might be
even zero bytes given how kernel allocators works)>

/Jarkko

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